| r0.1 | label_boi_a2/consolidated balance sheet - including banking corporations reported as a bank only | | | | N/A | N/A | boi_CS:x2 | N/A | boi_RP:x13 | N/A |
| 1.1 | Assets: Cash and deposits with banks/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x9 | boi_RP:x13 | boi_SE:x1 |
| 2.1 | Securities/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x29 | boi_RP:x13 | N/A |
| 3.1 | Securities borrowed or purchased under agreements to resale/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x28 | boi_RP:x13 | N/A |
| 4.1 | Credit to the public/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi2 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x8 | boi_RP:x13 | boi_SE:x16 |
| 5.1 | Alowence for loan losses/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x8 | boi_RP:x13 | boi_SE:x16 |
| 6.1 | Credit to the public, net/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x8 | boi_RP:x13 | boi_SE:x16 |
| 7.1 | Credit to government/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x8 | boi_RP:x13 | boi_SE:x11 |
| 8.1 | Investments in companies included on an equity basis/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x54 | boi_RP:x13 | N/A |
| 9.1 | Buildings and equipment/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x6 | boi_RP:x13 | N/A |
| 10.1 | Intangible assets and goodwill/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x19 | boi_RP:x13 | N/A |
| 11.1 | Assets-derivative instruments/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x18 | boi_RP:x13 | N/A |
| 12.1 | Other assets/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x41 | boi_RP:x13 | N/A |
| 13.1 | Total assets/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MC:x1 | boi_RP:x13 | N/A |
| 14.1 | liabilities: deposits of the public/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_MC:x17 | boi_RP:x13 | boi_SE:x16 |
| 15.1 | Deposits from banks/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_MC:x17 | boi_RP:x13 | boi_SE:x1 |
| 16.1 | Deposits from governments/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_MC:x17 | boi_RP:x13 | boi_SE:x11 |
| 17.1 | Securities loaned or sold under agreements to repurchase/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_MC:x28 | boi_RP:x13 | N/A |
| 18.1 | Debentures and subordinated notes/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_MC:x15 | boi_RP:x13 | N/A |
| 19.1 | Liabilities-derivative instruments/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_MC:x18 | boi_RP:x13 | N/A |
| 20.1 | Other liabilities/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_MC:x20 | boi_RP:x13 | N/A |
| 21.1 | Total liabilities/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | N/A | boi_CS:x2 | boi_MC:x3 | boi_RP:x13 | N/A |
| 22.1 | External shareholders rights/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x3 | boi_CN:x2 | boi_CS:x2 | boi_MC:x2 | boi_RP:x13 | N/A |
| 23.1 | Equity capital attributed to shareholders of the banking corporation/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x3 | boi_CN:x1 | boi_CS:x2 | boi_MC:x2 | boi_RP:x13 | N/A |
| 24.1 | Total equity/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x3 | N/A | boi_CS:x2 | boi_MC:x2 | boi_RP:x13 | N/A |
| 25.1 | Total liabilities and capital/consolidated balance sheet - including banking corporations reported as a bank only | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x4 | N/A | boi_CS:x2 | boi_MC:x4 | boi_RP:x13 | N/A |