| r0.1 | label_boi_a2/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | N/A | boi_RP:x25 |
| r1.1 | 2.1 Components of net benefit cost recognized in earnings statement/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 1.1 | Servicing cost/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1008 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 2.1 | Interest cost/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1009 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 3.1 | Foreseen return on plan assets/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1010 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| r5.1 | Subtraction of unrecognized sums/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | N/A | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 4.1 | Net actuarial loss (profit)/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1031 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 5.1 | Net liability (asset) on account of transition/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1032 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 6.1 | Previous servicing cost/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1033 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 7.1 | Total subtractions of unrecognized sums/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1011 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 8.1 | Other, incl. loss (profit) from reduction or settlement/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1015 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 9.1 | Total net benefit cost/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1007 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| r12.1 | 2.2 Recognized changes in plan assets and benefit liability in total other profit (loss) before effect of tax/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | boi_MU:x1 | N/A | boi_RP:x25 |
| 10.1 | Net actuarial loss (profit) during year/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_MC:x406 | boi_MU:x1 | boi_PL:x70 | boi_RP:x25 |
| 11.1 | Subtraction of actuarial profit (loss)/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_MC:x406 | boi_MU:x1 | boi_PL:x74 | boi_RP:x25 |
| 12.1 | Cost (credit) on account of previous servicing during year/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_MC:x406 | boi_MU:x1 | boi_PL:x72 | boi_RP:x25 |
| 13.1 | Subtraction of credit (cost) on account of previous servicing/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_MC:x406 | boi_MU:x1 | boi_PL:x75 | boi_RP:x25 |
| 14.1 | Subtraction of net liability (asset) on account of transition/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_MC:x406 | boi_MU:x1 | boi_PL:x76 | boi_RP:x25 |
| 15.1 | Changes in FX exchange rates/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_MC:x406 | boi_MU:x1 | boi_PL:x77 | boi_RP:x25 |
| 16.1 | Other, incl. loss (profit) from reduction or settlement/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_MC:x406 | boi_MU:x1 | boi_PL:x78 | boi_RP:x25 |
| 17.1 | Total recognized in total other profit/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_MC:x406 | boi_MU:x1 | boi_PL:x73 | boi_RP:x25 |
| 18.1 | Total net benefit cost/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x1007 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |
| 19.1 | Total recognized in net benefit cost during period and in total other profit/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_MC:x1016 | boi_MU:x1 | boi_PL:x69 | boi_RP:x25 |