| r0.1 | label_boi_a2/Credit to the public | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | N/A |
| r0.2 | label_boi_a2/Off-balance-sheet credit risk*** | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | N/A |
| r0.3 | label_boi_a2/Credit to the public | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | N/A |
| r0.4 | label_boi_a2/Off-balance-sheet credit risk*** | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | N/A |
| r0.5 | label_boi_a2/Credit to the public | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | N/A |
| r0.6 | label_boi_a2/Off-balance-sheet credit risk*** | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | N/A |
| 1.1 | Total commercial*/Credit to the public | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x4 |
| 1.2 | Total commercial*/Off-balance-sheet credit risk*** | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x4 |
| 1.3 | Total commercial*/Credit to the public | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x4 |
| 1.4 | Total commercial*/Off-balance-sheet credit risk*** | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x4 |
| 1.5 | Total commercial*/Credit to the public | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x4 |
| 1.6 | Total commercial*/Off-balance-sheet credit risk*** | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x4 |
| 2.1 | Private individuals - housing loans/Credit to the public | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x35 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 2.2 | Private individuals - housing loans/Off-balance-sheet credit risk*** | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x8 | boi_CL:x35 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 2.3 | Private individuals - housing loans/Credit to the public | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x35 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 2.4 | Private individuals - housing loans/Off-balance-sheet credit risk*** | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x8 | boi_CL:x35 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 2.5 | Private individuals - housing loans/Credit to the public | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x35 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 2.6 | Private individuals - housing loans/Off-balance-sheet credit risk*** | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x8 | boi_CL:x35 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 3.1 | Private individuals - other/Credit to the public | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x38 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 3.2 | Private individuals - other/Off-balance-sheet credit risk*** | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x8 | boi_CL:x38 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 3.3 | Private individuals - other/Credit to the public | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x38 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 3.4 | Private individuals - other/Off-balance-sheet credit risk*** | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x8 | boi_CL:x38 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 3.5 | Private individuals - other/Credit to the public | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x38 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 3.6 | Private individuals - other/Off-balance-sheet credit risk*** | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x8 | boi_CL:x38 | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x15 |
| 4.1 | Total credit risk to the public/Credit to the public | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x16 |
| 4.2 | Total credit risk to the public/Off-balance-sheet credit risk*** | boi_met:mi608 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x16 |
| 4.3 | Total credit risk to the public/Credit to the public | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x16 |
| 4.4 | Total credit risk to the public/Off-balance-sheet credit risk*** | boi_met:mi1220 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x16 |
| 4.5 | Total credit risk to the public/Credit to the public | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x16 |
| 4.6 | Total credit risk to the public/Off-balance-sheet credit risk*** | boi_met:mi1219 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | boi_CS:x2 | boi_MU:x1 | boi_RP:x24 | boi_SE:x16 |