| 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 | 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 | N/A | boi_RP:x25 |
| 1.1 | Total activity in 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:x16 | N/A | boi_RP:x25 |
| 1.2 | Total activity in 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:x16 | N/A | boi_RP:x25 |
| r2.1 | A.2. From investment in bonds/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | boi_MC:x15 | boi_MU:x1 | N/A | N/A | boi_RP:x25 |
| r2.2 | A.2. From investment in bonds/Company | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x1 | N/A | N/A | boi_MC:x15 | boi_MU:x1 | N/A | N/A | boi_RP:x25 |
| 2.1 | Profit from sale of bonds held to maturity/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x2 | N/A | boi_MC:x132 | boi_MC:x15 | boi_MU:x1 | boi_PL:x5 | N/A | boi_RP:x25 |
| 2.2 | Profit from sale of bonds held to maturity/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x1 | N/A | boi_MC:x132 | boi_MC:x15 | boi_MU:x1 | boi_PL:x5 | N/A | boi_RP:x25 |
| 3.1 | Loss from sale of bonds held to maturity/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | N/A | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x5 | N/A | boi_RP:x25 |
| 3.2 | Loss from sale of bonds held to maturity/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x1 | N/A | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x5 | N/A | boi_RP:x25 |
| 4.1 | Including provisions for impairment of/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x126 | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x5 | N/A | boi_RP:x25 |
| 4.2 | Including provisions for impairment of/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x1 | boi_MC:x126 | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x5 | N/A | boi_RP:x25 |
| 5.1 | Profit from sale of bonds available for sale/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x2 | N/A | boi_MC:x132 | boi_MC:x15 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 5.2 | Profit from sale of bonds available for sale/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x1 | N/A | boi_MC:x132 | boi_MC:x15 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 6.1 | Provision for impairment for bonds available for sale/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x126 | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 6.2 | Provision for impairment for bonds available for sale/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x1 | boi_MC:x126 | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 7.1 | Loss from sale of bonds available for sale/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | N/A | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 7.2 | Loss from sale of bonds available for sale/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x1 | N/A | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 8.1 | of which: for transfer of bonds to for-trading porftolio/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | N/A | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x1 | boi_PL:x2 | boi_RP:x25 |
| 8.2 | of which: for transfer of bonds to for-trading porftolio/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x1 | N/A | boi_MC:x133 | boi_MC:x15 | boi_MU:x1 | boi_PL:x1 | boi_PL:x2 | boi_RP:x25 |
| 9.1 | Total investment in bonds/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x131 | boi_MC:x15 | boi_MU:x1 | boi_PL:x14 | N/A | boi_RP:x25 |
| 9.2 | Total investment in bonds/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x131 | boi_MC:x15 | boi_MU:x1 | boi_PL:x14 | N/A | boi_RP:x25 |
| 10.1 | A.3. Exchange-rate differentials, net/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x139 | N/A | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 10.2 | A.3. Exchange-rate differentials, net/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x139 | N/A | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| r12.1 | A.4. Profit (loss) from investment in shares/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | N/A | boi_MU:x1 | N/A | N/A | boi_RP:x25 |
| r12.2 | A.4. Profit (loss) from investment in shares/Company | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x1 | N/A | N/A | N/A | boi_MU:x1 | N/A | N/A | boi_RP:x25 |
| 11.1 | Profit from sale of non trade shares/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x2 | N/A | boi_MC:x132 | boi_MC:x30 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 11.2 | Profit from sale of non trade shares/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x1 | N/A | boi_MC:x132 | boi_MC:x30 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 12.1 | Provision for write-down of non trade shares/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | boi_MC:x126 | boi_MC:x132 | boi_MC:x30 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 12.2 | Provision for write-down of non trade shares/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x1 | boi_MC:x126 | boi_MC:x132 | boi_MC:x30 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 13.1 | Losses from sale of non trade shares/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | N/A | boi_MC:x133 | boi_MC:x30 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 13.2 | Losses from sale of non trade shares/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x1 | N/A | boi_MC:x133 | boi_MC:x30 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 14.1 | Dividend from non trade shares/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x2 | N/A | boi_MC:x137 | boi_MC:x30 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 14.2 | Dividend from non trade shares/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x1 | N/A | boi_MC:x137 | boi_MC:x30 | boi_MU:x1 | boi_PL:x1 | N/A | boi_RP:x25 |
| 15.1 | Unrealised financial gains/losses/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:x1 | N/A | boi_RP:x25 |
| 15.2 | Unrealised financial gains/losses/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:x1 | N/A | boi_RP:x25 |
| 16.1 | Profit from sale of shares of held companies (consolidated / included)/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x2 | N/A | boi_MC:x132 | boi_MC:x54 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 16.2 | Profit from sale of shares of held companies (consolidated / included)/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x1 | N/A | boi_MC:x132 | boi_MC:x54 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 17.1 | Loss from sale of shares of held companies (consolidated / included)/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x2 | N/A | boi_MC:x133 | boi_MC:x54 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 17.2 | Loss from sale of shares of held companies (consolidated / included)/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x10 | boi_CS:x1 | N/A | boi_MC:x133 | boi_MC:x54 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 18.1 | Total investment in shares/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x129 | boi_MC:x246 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 18.2 | Total investment in shares/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x129 | boi_MC:x246 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 19.1 | A.5. Net profit (loss) from securitization transactions/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x131 | boi_MC:x138 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 19.2 | A.5. Net profit (loss) from securitization transactions/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x131 | boi_MC:x138 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 20.1 | A.6. Net profit (loss) from loans sold/Consolidated | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x131 | boi_MC:x140 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 20.2 | A.6. Net profit (loss) from loans sold/Company | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x1 | N/A | boi_MC:x131 | boi_MC:x140 | boi_MU:x1 | boi_PL:x15 | N/A | boi_RP:x25 |
| 21.1 | Total non-interest financing income from activities for other than trading purposes/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:x15 | N/A | boi_RP:x25 |
| 21.2 | Total non-interest financing income from activities for other than trading purposes/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:x15 | N/A | boi_RP:x25 |