| r0.1 | label_boi_a2/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | N/A | boi_MU:x1 | N/A | boi_RP:x25 |
| r0.2 | label_boi_a2/Company | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x1 | N/A | N/A | N/A | boi_MU:x1 | N/A | boi_RP:x25 |
| r1.1 | B. Non-interest financing on account of activities for trading purposes/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| r1.2 | B. Non-interest financing on account of activities for trading purposes/Company | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x1 | N/A | N/A | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 1.1 | Net income (expenses) on account of other derivatives/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 1.2 | Net income (expenses) on account of other derivatives/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 2.1 | Realized and non-yet-realized profit (loss) from fair-value adjustments of bonds for trading, net/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x130 | boi_MC:x15 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 2.2 | Realized and non-yet-realized profit (loss) from fair-value adjustments of bonds for trading, net/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x130 | boi_MC:x15 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 3.1 | Thereof: share of profit and loss associated with bonds for trading still held on balance-sheet date: __ (sum)/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x134 | boi_MC:x15 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 3.2 | Thereof: share of profit and loss associated with bonds for trading still held on balance-sheet date: __ (sum)/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x134 | boi_MC:x15 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 4.1 | Realized and non-yet-realized profit (loss) from fair-value adjustments of shares for trading, net/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x130 | boi_MC:x30 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 4.2 | Realized and non-yet-realized profit (loss) from fair-value adjustments of shares for trading, net/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x130 | boi_MC:x30 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 5.1 | Thereof: share of profit and loss associated with shares for trading still held on balance-sheet date: __ (sum)/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x134 | boi_MC:x30 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 5.2 | Thereof: share of profit and loss associated with shares for trading still held on balance-sheet date: __ (sum)/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x134 | boi_MC:x30 | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 6.1 | Dividends received on account of trading activities/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x2 | N/A | boi_MC:x137 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 6.2 | Dividends received on account of trading activities/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x1 | N/A | boi_MC:x137 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 7.1 | Total, trading activities/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 7.2 | Total, trading activities/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| r9.1 | Breakdown of non-interest financing income from activities for trading purposes, by risk exposure/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| r9.2 | Breakdown of non-interest financing income from activities for trading purposes, by risk exposure/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 8.1 | Interest exposure/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x22 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 8.2 | Interest exposure/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | boi_EC:x22 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 9.1 | Foreign currency exposure/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x23 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 9.2 | Foreign currency exposure/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | boi_EC:x23 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 10.1 | Share exposure/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x24 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 10.2 | Share exposure/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | boi_EC:x24 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 11.1 | Commodity and other exposure/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x25 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 11.2 | Commodity and other exposure/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | boi_EC:x25 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 12.1 | Total, trading activities/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| 12.2 | Total, trading activities/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x25 |
| r15.1 | C. Ineffective part of hedging ratios - additional breakdown/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | N/A | boi_RP:x25 |
| r15.2 | C. Ineffective part of hedging ratios - additional breakdown/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | N/A | boi_RP:x25 |
| r16.1 | Fair-value hedges:/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | N/A | boi_RP:x25 |
| r16.2 | Fair-value hedges:/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | N/A | boi_RP:x25 |
| 13.1 | ineffectiveness of hedges/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x20 | boi_RP:x25 |
| 13.2 | ineffectiveness of hedges/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x20 | boi_RP:x25 |
| 14.1 | Component of profit (loss) spent for evaluation of hedging effectiveness/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x21 | boi_RP:x25 |
| 14.2 | Component of profit (loss) spent for evaluation of hedging effectiveness/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x21 | boi_RP:x25 |
| 15.1 | Net profit (loss) from strong contractual relationship no longer qualifying as fair-value hedge/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x22 | boi_RP:x25 |
| 15.2 | Net profit (loss) from strong contractual relationship no longer qualifying as fair-value hedge/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x22 | boi_RP:x25 |
| r20.1 | Cash-flow hedges:/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | N/A | boi_RP:x25 |
| r20.2 | Cash-flow hedges:/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | N/A | boi_RP:x25 |
| 16.1 | ineffectiveness of hedges/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x23 | boi_RP:x25 |
| 16.2 | ineffectiveness of hedges/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x23 | boi_RP:x25 |
| 17.1 | Component of profit (loss) spent for evaluation of hedging effectiveness/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x24 | boi_RP:x25 |
| 17.2 | Component of profit (loss) spent for evaluation of hedging effectiveness/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x24 | boi_RP:x25 |
| 18.1 | Profit (loss) reclassified due to apparent non-performance of transactions/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x25 | boi_RP:x25 |
| 18.2 | Profit (loss) reclassified due to apparent non-performance of transactions/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x25 | boi_RP:x25 |
| 19.1 | Total/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x19 | boi_RP:x25 |
| 19.2 | Total/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x19 | boi_RP:x25 |