| r0.1 | label_boi_a2/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | N/A | boi_RP:x24 |
| r0.2 | label_boi_a2/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | N/A | boi_CS:x1 | N/A | N/A | N/A | boi_RP:x24 |
| r1.1 | Sources of securities received which the bank may sell or pledge,by fair value excluding set offs/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | N/A | N/A | N/A | boi_RP:x24 |
| r1.2 | Sources of securities received which the bank may sell or pledge,by fair value excluding set offs/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | N/A | N/A | N/A | boi_RP:x24 |
| 1.1 | Securities purchased under agreements to resell/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x815 | N/A | N/A | boi_RP:x24 |
| 1.2 | Securities purchased under agreements to resell/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x815 | N/A | N/A | boi_RP:x24 |
| 2.1 | Securities received in securities borrowing transactions against cash/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x816 | N/A | N/A | boi_RP:x24 |
| 2.2 | Securities received in securities borrowing transactions against cash/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x816 | N/A | N/A | boi_RP:x24 |
| 3.1 | Securities received as collateral for securities lending transactions against securities/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x817 | N/A | N/A | boi_RP:x24 |
| 3.2 | Securities received as collateral for securities lending transactions against securities/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x817 | N/A | N/A | boi_RP:x24 |
| 4.1 | Received securities borrowing transactions in securities against securities/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x818 | N/A | N/A | boi_RP:x24 |
| 4.2 | Received securities borrowing transactions in securities against securities/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x818 | N/A | N/A | boi_RP:x24 |
| 5.1 | Other/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x819 | N/A | N/A | boi_RP:x24 |
| 5.2 | Other/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x819 | N/A | N/A | boi_RP:x24 |
| 6.1 | Total/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x820 | N/A | N/A | boi_RP:x24 |
| 6.2 | Total/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x820 | N/A | N/A | boi_RP:x24 |
| r8.1 | The use of securities received as a collateral and bank securities by fair value 1:/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | N/A | N/A | N/A | boi_RP:x24 |
| r8.2 | The use of securities received as a collateral and bank securities by fair value 1:/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x1 | N/A | N/A | N/A | boi_RP:x24 |
| 7.1 | Securities saled under agreements to repurchase/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x821 | N/A | N/A | boi_RP:x24 |
| 7.2 | Securities saled under agreements to repurchase/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x1 | boi_MC:x821 | N/A | N/A | boi_RP:x24 |
| 8.1 | Securities loaned in securities lending transactions against cash/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x822 | N/A | N/A | boi_RP:x24 |
| 8.2 | Securities loaned in securities lending transactions against cash/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x1 | boi_MC:x822 | N/A | N/A | boi_RP:x24 |
| 9.1 | Securities borrowed on borrowing transactions in securities against securities/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x823 | N/A | N/A | boi_RP:x24 |
| 9.2 | Securities borrowed on borrowing transactions in securities against securities/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x1 | boi_MC:x823 | N/A | N/A | boi_RP:x24 |
| 10.1 | Securities pledged as a collatteral for securities borrowing transaction in securities against securities/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x824 | N/A | N/A | boi_RP:x24 |
| 10.2 | Securities pledged as a collatteral for securities borrowing transaction in securities against securities/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x1 | boi_MC:x824 | N/A | N/A | boi_RP:x24 |
| 11.1 | Other/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x825 | N/A | N/A | boi_RP:x24 |
| 11.2 | Other/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x1 | boi_MC:x825 | N/A | N/A | boi_RP:x24 |
| 12.1 | Total/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x826 | N/A | N/A | boi_RP:x24 |
| 12.2 | Total/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x1 | boi_MC:x826 | N/A | N/A | boi_RP:x24 |
| r15.1 | Details of pledged securities lenders (entitled to sell\pledged them)/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x29 | boi_MC:x991 | N/A | boi_RP:x24 |
| r15.2 | Details of pledged securities lenders (entitled to sell\pledged them)/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x29 | boi_MC:x991 | N/A | boi_RP:x24 |
| 13.1 | Securities/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x29 | boi_MC:x991 | boi_PL:x2 | boi_RP:x24 |
| 13.2 | Securities/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x29 | boi_MC:x991 | boi_PL:x2 | boi_RP:x24 |
| 14.1 | Securities available for sale/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x29 | boi_MC:x991 | boi_PL:x1 | boi_RP:x24 |
| 14.2 | Securities available for sale/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x29 | boi_MC:x991 | boi_PL:x1 | boi_RP:x24 |
| 15.1 | Securities held to maturity/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x29 | boi_MC:x991 | boi_PL:x5 | boi_RP:x24 |
| 15.2 | Securities held to maturity/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x29 | boi_MC:x991 | boi_PL:x5 | boi_RP:x24 |
| 16.1 | Total/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x29 | boi_MC:x991 | N/A | boi_RP:x24 |
| 16.2 | Total/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x29 | boi_MC:x991 | N/A | boi_RP:x24 |
| 17.1 | Securities provided as a collateral to lenders who are not allowed to sell\pledged them 2/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x29 | boi_MC:x827 | N/A | boi_RP:x24 |
| 17.2 | Securities provided as a collateral to lenders who are not allowed to sell\pledged them 2/Bank Corporation | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x1 | boi_MC:x29 | boi_MC:x827 | N/A | boi_RP:x24 |