| r0.1 | label_boi_a2/Consolidated | | | | N/A | boi_CS:x2 | N/A | N/A | N/A | boi_RP:x24 | N/A |
| r1.1 | 1.1 Change in foreseen benefit liability/Consolidated | | | | N/A | boi_CS:x2 | N/A | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 1.1 | Foreseen benefit liability at beginning of year/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x1023 | N/A | boi_PL:x69 | boi_RP:x24 | boi_RP:x22 |
| 2.1 | Servicing cost/Consolidated | boi_met:md872 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 3.1 | Interest cost/Consolidated | boi_met:md873 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 4.1 | Program participants' deposits/Consolidated | boi_met:md874 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 5.1 | Actuarial loss (profit)/Consolidated | boi_met:md875 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 6.1 | Changes in FX exchange rates/Consolidated | boi_met:md876 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 7.1 | Benefits paid out/Consolidated | boi_met:md877 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 8.1 | Adjustments of plan/Consolidated | boi_met:md878 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 9.1 | Adjustments of plan/Consolidated | boi_met:md1221 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 10.1 | Cutbacks, settlements/Consolidated | boi_met:md1222 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 11.1 | Other/Consolidated | boi_met:md880 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 12.1 | Foreseen benefit liability at end of year/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x1023 | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 13.1 | State of funding - net recognized asset (liability) at end of year/Consolidated | boi_met:md888 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x1023 | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| r15.1 | 1.2 Change in fair value of plan assets and state of plan funding/Consolidated | | | | N/A | boi_CS:x2 | N/A | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 14.1 | Fair value of plan assets at beginning of year/Consolidated | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x1024 | N/A | boi_PL:x69 | boi_RP:x24 | boi_RP:x22 |
| 15.1 | Actual return on plan assets/Consolidated | boi_met:md881 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 16.1 | Changes in FX exchange rates/Consolidated | boi_met:md882 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 17.1 | Deposits in plan by banking corp./Consolidated | boi_met:md883 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 18.1 | Deposits in plan by employees/Consolidated | boi_met:md884 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 19.1 | Benefits paid out/Consolidated | boi_met:md885 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 20.1 | Settlements/Consolidated | boi_met:md886 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 21.1 | Other/Consolidated | boi_met:md887 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x24 | N/A |
| 22.1 | Fair value of plan assets at end of year/Consolidated | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x1024 | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 23.1 | State of funding - net recognized asset (liability) at end of year/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x5 | boi_CS:x2 | boi_MC:x432 | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| r26.1 | 1.3 Sums recognized on consolidated balance sheet/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | boi_MC:x432 | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 24.1 | Sums recognized on Other Assets line/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_MC:x432 | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 25.1 | Sums recognized on Other Liabilities line/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_MC:x432 | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 26.1 | Net asset (liability) recognized at end of year/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x5 | boi_CS:x2 | boi_MC:x432 | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| r30.1 | 1.4 Sums recognized in total other cumulative profit (loss) before effect of tax/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x3 | boi_CS:x2 | boi_MC:x406 | N/A | N/A | boi_RP:x24 | N/A |
| 27.1 | Net actuarial loss (profit)/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x3 | boi_CS:x2 | boi_MC:x406 | N/A | boi_PL:x70 | boi_RP:x24 | N/A |
| 28.1 | Net liability (asset) on account of transition/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x3 | boi_CS:x2 | boi_MC:x406 | N/A | boi_PL:x71 | boi_RP:x24 | N/A |
| 29.1 | Net cost (credit) on account of previous servicing/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x3 | boi_CS:x2 | boi_MC:x406 | N/A | boi_PL:x72 | boi_RP:x24 | N/A |
| 30.1 | Closing balance of total cumulative other profit/Consolidated | boi_met:mi1 | xbrli:monetaryItemType | instant | boi_BC:x3 | boi_CS:x2 | boi_MC:x406 | N/A | boi_PL:x73 | boi_RP:x24 | N/A |
| r35.1 | 1.5 Plans in which cumulative benefit liability exceeds plan assets/Consolidated | | | | N/A | boi_CS:x2 | N/A | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 31.1 | Foreseen benefit liability/Consolidated | boi_met:mi889 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 32.1 | Cumulative benefit liaiblity/Consolidated | boi_met:mi890 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 33.1 | Fair value of plan assets/Consolidated | boi_met:mi891 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| r39.1 | 1.6 Plans in which foreseen benefit liability exceeds plan assets/Consolidated | | | | N/A | boi_CS:x2 | N/A | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 34.1 | Foreseen benefit liability/Consolidated | boi_met:mi892 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | boi_PL:x69 | boi_RP:x24 | N/A |
| 35.1 | Fair value of plan assets/Consolidated | boi_met:mi893 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | boi_PL:x69 | boi_RP:x24 | N/A |