| r0.1 | label_boi_a2/Trading activity | | | | N/A | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| r0.2 | label_boi_a2/Asset and liability mgmt. activity | | | | N/A | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| r0.3 | label_boi_a2/Real investment activity | | | | N/A | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| r0.4 | label_boi_a2/Other | | | | N/A | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| r0.5 | label_boi_a2/Total | | | | N/A | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 1.1 | Interest income from outside segment/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | boi_SE:x44 |
| 1.2 | Interest income from outside segment/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | boi_SE:x44 |
| 1.3 | Interest income from outside segment/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | boi_SE:x44 |
| 1.4 | Interest income from outside segment/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | boi_SE:x44 |
| 1.5 | Interest income from outside segment/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | boi_SE:x44 |
| 2.1 | Interest expenditure to outside segment/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | boi_SE:x44 |
| 2.2 | Interest expenditure to outside segment/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | boi_SE:x44 |
| 2.3 | Interest expenditure to outside segment/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | boi_SE:x44 |
| 2.4 | Interest expenditure to outside segment/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | boi_SE:x44 |
| 2.5 | Interest expenditure to outside segment/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | boi_SE:x44 |
| r3.1 | Interest income, net:/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| r3.2 | Interest income, net:/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| r3.3 | Interest income, net:/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| r3.4 | Interest income, net:/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| r3.5 | Interest income, net:/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 3.1 | From outside segment/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | boi_SE:x44 |
| 3.2 | From outside segment/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | boi_SE:x44 |
| 3.3 | From outside segment/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | boi_SE:x44 |
| 3.4 | From outside segment/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | boi_SE:x44 |
| 3.5 | From outside segment/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | boi_SE:x44 |
| 4.1 | From within segment/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | boi_SE:x45 |
| 4.2 | From within segment/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | boi_SE:x45 |
| 4.3 | From within segment/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | boi_SE:x45 |
| 4.4 | From within segment/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | boi_SE:x45 |
| 4.5 | From within segment/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | boi_SE:x45 |
| 5.1 | Total interest income, net/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 5.2 | Total interest income, net/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 5.3 | Total interest income, net/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 5.4 | Total interest income, net/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 5.5 | Total interest income, net/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x125 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| r7.1 | Non-interest income:/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| r7.2 | Non-interest income:/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| r7.3 | Non-interest income:/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| r7.4 | Non-interest income:/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| r7.5 | Non-interest income:/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 6.1 | From outside segment/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | boi_SE:x44 |
| 6.2 | From outside segment/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | boi_SE:x44 |
| 6.3 | From outside segment/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | boi_SE:x44 |
| 6.4 | From outside segment/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | boi_SE:x44 |
| 6.5 | From outside segment/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | boi_SE:x44 |
| 7.1 | From within segment/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | boi_SE:x45 |
| 7.2 | From within segment/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | boi_SE:x45 |
| 7.3 | From within segment/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | boi_SE:x45 |
| 7.4 | From within segment/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | boi_SE:x45 |
| 7.5 | From within segment/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | boi_SE:x45 |
| 8.1 | Total non-interest income/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 8.2 | Total non-interest income/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 8.3 | Total non-interest income/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 8.4 | Total non-interest income/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 8.5 | Total non-interest income/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x127 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 9.1 | Total income/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 9.2 | Total income/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 9.3 | Total income/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 9.4 | Total income/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 9.5 | Total income/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 10.1 | Credit-loss expenditure/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x126 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 10.2 | Credit-loss expenditure/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x126 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 10.3 | Credit-loss expenditure/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x126 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 10.4 | Credit-loss expenditure/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x126 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 10.5 | Credit-loss expenditure/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x126 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| r13.1 | Operating and other expenses/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| r13.2 | Operating and other expenses/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| r13.3 | Operating and other expenses/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| r13.4 | Operating and other expenses/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| r13.5 | Operating and other expenses/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 11.1 | To outside segment/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | boi_SE:x44 |
| 11.2 | To outside segment/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | boi_SE:x44 |
| 11.3 | To outside segment/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | boi_SE:x44 |
| 11.4 | To outside segment/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | boi_SE:x44 |
| 11.5 | To outside segment/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | boi_SE:x44 |
| 12.1 | To within segment/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | boi_SE:x45 |
| 12.2 | To within segment/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | boi_SE:x45 |
| 12.3 | To within segment/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | boi_SE:x45 |
| 12.4 | To within segment/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | boi_SE:x45 |
| 12.5 | To within segment/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | boi_SE:x45 |
| 13.1 | Total operating and other expenses/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 13.2 | Total operating and other expenses/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 13.3 | Total operating and other expenses/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 13.4 | Total operating and other expenses/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 13.5 | Total operating and other expenses/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x160 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 14.1 | Pre-tax profit/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x123 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 14.2 | Pre-tax profit/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x123 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 14.3 | Pre-tax profit/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x123 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 14.4 | Pre-tax profit/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x123 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 14.5 | Pre-tax profit/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x123 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 15.1 | Provision for taxes on profit/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x190 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 15.2 | Provision for taxes on profit/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x190 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 15.3 | Provision for taxes on profit/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x190 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 15.4 | Provision for taxes on profit/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x190 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 15.5 | Provision for taxes on profit/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x12 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x190 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 16.1 | Post-tax profit/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x122 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 16.2 | Post-tax profit/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x122 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 16.3 | Post-tax profit/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x122 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 16.4 | Post-tax profit/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x122 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 16.5 | Post-tax profit/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x122 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 17.1 | Share of banking corp. in profits of included companies/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x191 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 17.2 | Share of banking corp. in profits of included companies/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x191 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 17.3 | Share of banking corp. in profits of included companies/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x191 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 17.4 | Share of banking corp. in profits of included companies/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x191 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 17.5 | Share of banking corp. in profits of included companies/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x191 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 18.1 | Net profit before attribution to holders of rights that do not confer control/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 18.2 | Net profit before attribution to holders of rights that do not confer control/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 18.3 | Net profit before attribution to holders of rights that do not confer control/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 18.4 | Net profit before attribution to holders of rights that do not confer control/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 18.5 | Net profit before attribution to holders of rights that do not confer control/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 19.1 | Net profit attributed to holders of rights that do not confer control/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x2 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 19.2 | Net profit attributed to holders of rights that do not confer control/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x2 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 19.3 | Net profit attributed to holders of rights that do not confer control/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x2 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 19.4 | Net profit attributed to holders of rights that do not confer control/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x2 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 19.5 | Net profit attributed to holders of rights that do not confer control/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x2 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 20.1 | Net profit attributed to shareholders in banking corp./Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x1 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 20.2 | Net profit attributed to shareholders in banking corp./Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x1 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 20.3 | Net profit attributed to shareholders in banking corp./Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x1 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 20.4 | Net profit attributed to shareholders in banking corp./Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x1 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 20.5 | Net profit attributed to shareholders in banking corp./Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CN:x1 | boi_CS:x2 | boi_GA:x1 | boi_MC:x121 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 21.1 | Avg. asset balance/Trading activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 21.2 | Avg. asset balance/Asset and liability mgmt. activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 21.3 | Avg. asset balance/Real investment activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 21.4 | Avg. asset balance/Other | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 21.5 | Avg. asset balance/Total | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 22.1 | Of which: Investments in included companies/Trading activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x54 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 22.2 | Of which: Investments in included companies/Asset and liability mgmt. activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x54 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 22.3 | Of which: Investments in included companies/Real investment activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x54 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 22.4 | Of which: Investments in included companies/Other | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x54 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 22.5 | Of which: Investments in included companies/Total | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x54 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 23.1 | Avg. liability balance/Trading activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x3 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 23.2 | Avg. liability balance/Asset and liability mgmt. activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x3 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 23.3 | Avg. liability balance/Real investment activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x3 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 23.4 | Avg. liability balance/Other | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x3 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 23.5 | Avg. liability balance/Total | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x3 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 24.1 | Of which: Avg. balance of deposits of the public/Trading activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | boi_SE:x339 | N/A |
| 24.2 | Of which: Avg. balance of deposits of the public/Asset and liability mgmt. activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | boi_SE:x299 | N/A |
| 24.3 | Of which: Avg. balance of deposits of the public/Real investment activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | boi_SE:x331 | N/A |
| 24.4 | Of which: Avg. balance of deposits of the public/Other | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | boi_SE:x329 | N/A |
| 24.5 | Of which: Avg. balance of deposits of the public/Total | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | N/A | N/A |
| 25.1 | Balance of deposits of the public at end of reporting period/Trading activity | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | N/A | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | boi_SE:x339 | N/A |
| 25.2 | Balance of deposits of the public at end of reporting period/Asset and liability mgmt. activity | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | N/A | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | boi_SE:x299 | N/A |
| 25.3 | Balance of deposits of the public at end of reporting period/Real investment activity | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | N/A | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | boi_SE:x331 | N/A |
| 25.4 | Balance of deposits of the public at end of reporting period/Other | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | N/A | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | boi_SE:x329 | N/A |
| 25.5 | Balance of deposits of the public at end of reporting period/Total | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x17 | N/A | boi_RP:x24 | boi_SE:x304 | boi_SE:x16 | N/A | N/A |
| 26.1 | Avg. balance of risk assets/Trading activity | boi_met:md88 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 26.2 | Avg. balance of risk assets/Asset and liability mgmt. activity | boi_met:md88 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 26.3 | Avg. balance of risk assets/Real investment activity | boi_met:md88 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 26.4 | Avg. balance of risk assets/Other | boi_met:md88 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 26.5 | Avg. balance of risk assets/Total | boi_met:md88 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 27.1 | Balance of risk assets at end of reporting period/Trading activity | boi_met:mi30 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 27.2 | Balance of risk assets at end of reporting period/Asset and liability mgmt. activity | boi_met:mi30 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 27.3 | Balance of risk assets at end of reporting period/Real investment activity | boi_met:mi30 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 27.4 | Balance of risk assets at end of reporting period/Other | boi_met:mi30 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 27.5 | Balance of risk assets at end of reporting period/Total | boi_met:mi30 | xbrli:monetaryItemType | instant | boi_BC:x16 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | N/A | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 28.1 | Avg. balance of assets managed/Trading activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x29 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x262 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 28.2 | Avg. balance of assets managed/Asset and liability mgmt. activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x29 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x262 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 28.3 | Avg. balance of assets managed/Real investment activity | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x29 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x262 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 28.4 | Avg. balance of assets managed/Other | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x29 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x262 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 28.5 | Avg. balance of assets managed/Total | boi_met:md1064 | xbrli:monetaryItemType | instant | boi_BC:x29 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x262 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| r32.1 | Components of net interest income and non-interest income/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| r32.2 | Components of net interest income and non-interest income/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| r32.3 | Components of net interest income and non-interest income/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| r32.4 | Components of net interest income and non-interest income/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| r32.5 | Components of net interest income and non-interest income/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | N/A | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 29.1 | Exchange-rate differentials, net/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x139 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 29.2 | Exchange-rate differentials, net/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x139 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 29.3 | Exchange-rate differentials, net/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x139 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 29.4 | Exchange-rate differentials, net/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x139 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 29.5 | Exchange-rate differentials, net/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x139 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 30.1 | Index differentials, net/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1034 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 30.2 | Index differentials, net/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1034 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 30.3 | Index differentials, net/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1034 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 30.4 | Index differentials, net/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1034 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 30.5 | Index differentials, net/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1034 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 31.1 | Interest-rate exposures, net/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1035 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 31.2 | Interest-rate exposures, net/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1035 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 31.3 | Interest-rate exposures, net/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1035 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 31.4 | Interest-rate exposures, net/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1035 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 31.5 | Interest-rate exposures, net/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1035 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 32.1 | Equities exposures, net/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1036 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 32.2 | Equities exposures, net/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1036 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 32.3 | Equities exposures, net/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1036 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 32.4 | Equities exposures, net/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1036 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 32.5 | Equities exposures, net/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1036 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 33.1 | Interest spreads attributed to financial management/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1037 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 33.2 | Interest spreads attributed to financial management/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1037 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 33.3 | Interest spreads attributed to financial management/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1037 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 33.4 | Interest spreads attributed to financial management/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1037 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 33.5 | Interest spreads attributed to financial management/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1037 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 34.1 | Total net interest income and non-interest income, on accrual basis/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1038 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 34.2 | Total net interest income and non-interest income, on accrual basis/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1038 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 34.3 | Total net interest income and non-interest income, on accrual basis/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1038 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 34.4 | Total net interest income and non-interest income, on accrual basis/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1038 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 34.5 | Total net interest income and non-interest income, on accrual basis/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1038 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 35.1 | Profits or losses on sale or non-temporary loss of value of bonds/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1039 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 35.2 | Profits or losses on sale or non-temporary loss of value of bonds/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1039 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 35.3 | Profits or losses on sale or non-temporary loss of value of bonds/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1039 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 35.4 | Profits or losses on sale or non-temporary loss of value of bonds/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1039 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 35.5 | Profits or losses on sale or non-temporary loss of value of bonds/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1039 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 36.1 | Change in spread between fair value and accrual basis of derivatives, recorded in earnings statement/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1040 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 36.2 | Change in spread between fair value and accrual basis of derivatives, recorded in earnings statement/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1040 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 36.3 | Change in spread between fair value and accrual basis of derivatives, recorded in earnings statement/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1040 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 36.4 | Change in spread between fair value and accrual basis of derivatives, recorded in earnings statement/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1040 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 36.5 | Change in spread between fair value and accrual basis of derivatives, recorded in earnings statement/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1040 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 37.1 | Other Non-interest income:/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1041 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 37.2 | Other Non-interest income:/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1041 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 37.3 | Other Non-interest income:/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1041 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 37.4 | Other Non-interest income:/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1041 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 37.5 | Other Non-interest income:/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x1041 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |
| 38.1 | Total net interest income and non-interest income/Trading activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x339 | N/A |
| 38.2 | Total net interest income and non-interest income/Asset and liability mgmt. activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x299 | N/A |
| 38.3 | Total net interest income and non-interest income/Real investment activity | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x331 | N/A |
| 38.4 | Total net interest income and non-interest income/Other | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | boi_SE:x329 | N/A |
| 38.5 | Total net interest income and non-interest income/Total | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | N/A | boi_CS:x2 | boi_GA:x1 | boi_MC:x455 | boi_MU:x1 | boi_RP:x24 | boi_SE:x304 | N/A | N/A | N/A |