| r0.1 | label_boi_a2/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | N/A | N/A | N/A | boi_CS:x1 | N/A | N/A | boi_MU:x1 | N/A | N/A | N/A | N/A | N/A | N/A |
| r0.2 | label_boi_a2/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | N/A | N/A | N/A | boi_CS:x1 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| r0.3 | label_boi_a2/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | N/A | N/A | N/A | boi_CS:x1 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| r0.4 | label_boi_a2/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | N/A | N/A | N/A | boi_CS:x1 | N/A | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | N/A | N/A | N/A |
| r0.5 | label_boi_a2/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | N/A | N/A | N/A | boi_CS:x1 | N/A | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | N/A | N/A | N/A |
| r0.6 | label_boi_a2/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | N/A | N/A | N/A | boi_CS:x2 | N/A | N/A | boi_MU:x1 | N/A | N/A | N/A | N/A | N/A | N/A |
| r0.7 | label_boi_a2/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | N/A | N/A | N/A | boi_CS:x2 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| r0.8 | label_boi_a2/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | N/A | N/A | N/A | boi_CS:x2 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| r1.1 | A. Balance sheet credit to the public/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| r1.2 | A. Balance sheet credit to the public/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| r1.3 | A. Balance sheet credit to the public/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| r1.4 | A. Balance sheet credit to the public/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | N/A | N/A | N/A |
| r1.5 | A. Balance sheet credit to the public/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | N/A | N/A | N/A |
| r1.6 | A. Balance sheet credit to the public/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| r1.7 | A. Balance sheet credit to the public/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| r1.8 | A. Balance sheet credit to the public/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| 1.1 | Impaired*/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x3 | N/A | N/A |
| 1.2 | Impaired*/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x3 | N/A | N/A |
| 1.3 | Impaired*/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x3 | N/A | N/A |
| 1.4 | Impaired*/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | boi_ST:x3 | N/A | N/A |
| 1.5 | Impaired*/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | boi_ST:x3 | N/A | N/A |
| 1.6 | Impaired*/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x3 | N/A | N/A |
| 1.7 | Impaired*/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x3 | N/A | N/A |
| 1.8 | Impaired*/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x3 | N/A | N/A |
| 2.1 | Substandard/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x15 | N/A | N/A |
| 2.2 | Substandard/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x15 | N/A | N/A |
| 2.3 | Substandard/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x15 | N/A | N/A |
| 2.4 | Substandard/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | boi_ST:x15 | N/A | N/A |
| 2.5 | Substandard/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | boi_ST:x15 | N/A | N/A |
| 2.6 | Substandard/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x15 | N/A | N/A |
| 2.7 | Substandard/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x15 | N/A | N/A |
| 2.8 | Substandard/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x15 | N/A | N/A |
| 3.1 | Under special supervision/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x14 | N/A | N/A |
| 3.2 | Under special supervision/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x14 | N/A | N/A |
| 3.3 | Under special supervision/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x14 | N/A | N/A |
| 3.4 | Under special supervision/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | boi_ST:x14 | N/A | N/A |
| 3.5 | Under special supervision/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | boi_ST:x14 | N/A | N/A |
| 3.6 | Under special supervision/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x14 | N/A | N/A |
| 3.7 | Under special supervision/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x14 | N/A | N/A |
| 3.8 | Under special supervision/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x14 | N/A | N/A |
| 4.1 | Not problematic**/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x1 | N/A | N/A |
| 4.2 | Not problematic**/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x1 | N/A | N/A |
| 4.3 | Not problematic**/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x1 | N/A | N/A |
| 4.4 | Not problematic**/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | boi_ST:x1 | N/A | N/A |
| 4.5 | Not problematic**/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | boi_ST:x1 | N/A | N/A |
| 4.6 | Not problematic**/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x1 | N/A | N/A |
| 4.7 | Not problematic**/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x1 | N/A | N/A |
| 4.8 | Not problematic**/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | boi_ST:x1 | N/A | N/A |
| 5.1 | Total excluding loans for housing/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | N/A | N/A | N/A |
| 5.2 | Total excluding loans for housing/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | N/A | N/A | N/A |
| 5.3 | Total excluding loans for housing/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | N/A | N/A | N/A |
| 5.4 | Total excluding loans for housing/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | N/A | N/A | N/A |
| 5.5 | Total excluding loans for housing/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x74 | N/A | N/A | N/A |
| 5.6 | Total excluding loans for housing/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x74 | N/A | N/A | N/A |
| 5.7 | Total excluding loans for housing/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | N/A | N/A | N/A |
| 5.8 | Total excluding loans for housing/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x74 | N/A | N/A | N/A |
| 6.1 | Loans for housing/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | boi_CL:x35 | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x96 | N/A | N/A | N/A |
| 6.2 | Loans for housing/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x35 | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x96 | N/A | N/A | N/A |
| 6.3 | Loans for housing/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x35 | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x96 | N/A | N/A | N/A |
| 6.4 | Loans for housing/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x35 | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x96 | N/A | N/A | N/A |
| 6.5 | Loans for housing/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x35 | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | boi_ST:x96 | N/A | N/A | N/A |
| 6.6 | Loans for housing/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | boi_CL:x35 | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | boi_ST:x96 | N/A | N/A | N/A |
| 6.7 | Loans for housing/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x35 | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x96 | N/A | N/A | N/A |
| 6.8 | Loans for housing/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CL:x35 | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | boi_ST:x96 | N/A | N/A | N/A |
| 7.1 | Total/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| 7.2 | Total/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| 7.3 | Total/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| 7.4 | Total/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | N/A | N/A | N/A |
| 7.5 | Total/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | N/A | N/A | N/A |
| 7.6 | Total/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| 7.7 | Total/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| 7.8 | Total/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | N/A | N/A | N/A |
| r9.1 | B. Deposits at banks and credit to governments/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| r9.2 | B. Deposits at banks and credit to governments/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| r9.3 | B. Deposits at banks and credit to governments/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| r9.4 | B. Deposits at banks and credit to governments/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | N/A | N/A | N/A |
| r9.5 | B. Deposits at banks and credit to governments/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | N/A | N/A | N/A |
| r9.6 | B. Deposits at banks and credit to governments/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| r9.7 | B. Deposits at banks and credit to governments/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| r9.8 | B. Deposits at banks and credit to governments/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| 8.1 | Impaired/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | boi_ST:x3 | N/A | N/A |
| 8.2 | Impaired/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x3 | N/A | N/A |
| 8.3 | Impaired/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x3 | N/A | N/A |
| 8.4 | Impaired/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | boi_ST:x3 | N/A | N/A |
| 8.5 | Impaired/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | boi_ST:x3 | N/A | N/A |
| 8.6 | Impaired/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | boi_ST:x3 | N/A | N/A |
| 8.7 | Impaired/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x3 | N/A | N/A |
| 8.8 | Impaired/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x3 | N/A | N/A |
| 9.1 | Substandard/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | boi_ST:x15 | N/A | N/A |
| 9.2 | Substandard/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x15 | N/A | N/A |
| 9.3 | Substandard/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x15 | N/A | N/A |
| 9.4 | Substandard/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | boi_ST:x15 | N/A | N/A |
| 9.5 | Substandard/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | boi_ST:x15 | N/A | N/A |
| 9.6 | Substandard/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | boi_ST:x15 | N/A | N/A |
| 9.7 | Substandard/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x15 | N/A | N/A |
| 9.8 | Substandard/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x15 | N/A | N/A |
| 10.1 | Under special supervision/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | boi_ST:x14 | N/A | N/A |
| 10.2 | Under special supervision/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x14 | N/A | N/A |
| 10.3 | Under special supervision/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x14 | N/A | N/A |
| 10.4 | Under special supervision/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | boi_ST:x14 | N/A | N/A |
| 10.5 | Under special supervision/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | boi_ST:x14 | N/A | N/A |
| 10.6 | Under special supervision/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | boi_ST:x14 | N/A | N/A |
| 10.7 | Under special supervision/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x14 | N/A | N/A |
| 10.8 | Under special supervision/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x14 | N/A | N/A |
| 11.1 | Not problematic/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | boi_ST:x1 | N/A | N/A |
| 11.2 | Not problematic/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x1 | N/A | N/A |
| 11.3 | Not problematic/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x1 | N/A | N/A |
| 11.4 | Not problematic/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | boi_ST:x1 | N/A | N/A |
| 11.5 | Not problematic/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | boi_ST:x1 | N/A | N/A |
| 11.6 | Not problematic/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | boi_ST:x1 | N/A | N/A |
| 11.7 | Not problematic/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x1 | N/A | N/A |
| 11.8 | Not problematic/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | boi_ST:x1 | N/A | N/A |
| 12.1 | Total/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| 12.2 | Total/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| 12.3 | Total/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| 12.4 | Total/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | N/A | N/A | N/A |
| 12.5 | Total/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x77 | N/A | N/A | N/A | N/A |
| 12.6 | Total/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| 12.7 | Total/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| 12.8 | Total/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x77 | N/A | N/A | N/A | N/A |
| r15.1 | C. Off balance sheet credit instruments/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | N/A | N/A | N/A |
| r15.2 | C. Off balance sheet credit instruments/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| r15.3 | C. Off balance sheet credit instruments/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| r15.4 | C. Off balance sheet credit instruments/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | N/A | N/A | N/A |
| r15.5 | C. Off balance sheet credit instruments/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | N/A | N/A | N/A |
| r15.6 | C. Off balance sheet credit instruments/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | N/A | N/A | N/A |
| r15.7 | C. Off balance sheet credit instruments/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| r15.8 | C. Off balance sheet credit instruments/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| 13.1 | Impaired/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | boi_ST:x3 | N/A | N/A |
| 13.2 | Impaired/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x3 | N/A | N/A |
| 13.3 | Impaired/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x3 | N/A | N/A |
| 13.4 | Impaired/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | boi_ST:x3 | N/A | N/A |
| 13.5 | Impaired/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | boi_ST:x3 | N/A | N/A |
| 13.6 | Impaired/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | boi_ST:x3 | N/A | N/A |
| 13.7 | Impaired/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x3 | N/A | N/A |
| 13.8 | Impaired/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x3 | N/A | N/A |
| 14.1 | Substandard/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | boi_ST:x15 | N/A | N/A |
| 14.2 | Substandard/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x15 | N/A | N/A |
| 14.3 | Substandard/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x15 | N/A | N/A |
| 14.4 | Substandard/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | boi_ST:x15 | N/A | N/A |
| 14.5 | Substandard/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | boi_ST:x15 | N/A | N/A |
| 14.6 | Substandard/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | boi_ST:x15 | N/A | N/A |
| 14.7 | Substandard/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x15 | N/A | N/A |
| 14.8 | Substandard/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x15 | N/A | N/A |
| 15.1 | Under special supervision/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | boi_ST:x14 | N/A | N/A |
| 15.2 | Under special supervision/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x14 | N/A | N/A |
| 15.3 | Under special supervision/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x14 | N/A | N/A |
| 15.4 | Under special supervision/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | boi_ST:x14 | N/A | N/A |
| 15.5 | Under special supervision/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | boi_ST:x14 | N/A | N/A |
| 15.6 | Under special supervision/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | boi_ST:x14 | N/A | N/A |
| 15.7 | Under special supervision/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x14 | N/A | N/A |
| 15.8 | Under special supervision/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x14 | N/A | N/A |
| 16.1 | Not problematic/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | boi_ST:x1 | N/A | N/A |
| 16.2 | Not problematic/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x1 | N/A | N/A |
| 16.3 | Not problematic/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x1 | N/A | N/A |
| 16.4 | Not problematic/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | boi_ST:x1 | N/A | N/A |
| 16.5 | Not problematic/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | boi_ST:x1 | N/A | N/A |
| 16.6 | Not problematic/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | boi_ST:x1 | N/A | N/A |
| 16.7 | Not problematic/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x1 | N/A | N/A |
| 16.8 | Not problematic/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | boi_ST:x1 | N/A | N/A |
| 17.1 | Total/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | N/A | N/A | N/A |
| 17.2 | Total/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| 17.3 | Total/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| 17.4 | Total/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | N/A | N/A | N/A |
| 17.5 | Total/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x1 | boi_MC:x65 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | N/A | N/A | N/A |
| 17.6 | Total/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | boi_MU:x1 | N/A | N/A | N/A | N/A | N/A | N/A |
| 17.7 | Total/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| 17.8 | Total/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x8 | N/A | N/A | boi_CS:x2 | boi_MC:x65 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| 18.1 | Total balance sheet and off balance sheet/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x28 | N/A | N/A | boi_CS:x1 | boi_MC:x704 | N/A | boi_MU:x1 | N/A | N/A | N/A | N/A | N/A | N/A |
| 18.2 | Total balance sheet and off balance sheet/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x28 | N/A | N/A | boi_CS:x1 | boi_MC:x704 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| 18.3 | Total balance sheet and off balance sheet/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x28 | N/A | N/A | boi_CS:x1 | boi_MC:x704 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| 18.4 | Total balance sheet and off balance sheet/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x28 | N/A | N/A | boi_CS:x1 | boi_MC:x704 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | N/A | N/A | N/A |
| 18.5 | Total balance sheet and off balance sheet/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x28 | N/A | N/A | boi_CS:x1 | boi_MC:x704 | N/A | boi_MU:x1 | boi_RP:x28 | N/A | N/A | N/A | N/A | N/A |
| 18.6 | Total balance sheet and off balance sheet/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x28 | N/A | N/A | boi_CS:x2 | boi_MC:x704 | N/A | boi_MU:x1 | N/A | N/A | N/A | N/A | N/A | N/A |
| 18.7 | Total balance sheet and off balance sheet/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x28 | N/A | N/A | boi_CS:x2 | boi_MC:x704 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| 18.8 | Total balance sheet and off balance sheet/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x28 | N/A | N/A | boi_CS:x2 | boi_MC:x704 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| 19.1 | Of which: Guarantees5 and exclusions permitted by Proper Conduct of Banking Business Directive 313 of nonacrruing impaired debts*/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | boi_CL:x42 | boi_CS:x1 | boi_MC:x8 | boi_MC:x914 | boi_MU:x1 | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 19.2 | Of which: Guarantees5 and exclusions permitted by Proper Conduct of Banking Business Directive 313 of nonacrruing impaired debts*/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CL:x42 | boi_CS:x1 | boi_MC:x8 | boi_MC:x914 | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 19.3 | Of which: Guarantees5 and exclusions permitted by Proper Conduct of Banking Business Directive 313 of nonacrruing impaired debts*/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CL:x42 | boi_CS:x1 | boi_MC:x8 | boi_MC:x914 | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 19.4 | Of which: Guarantees5 and exclusions permitted by Proper Conduct of Banking Business Directive 313 of nonacrruing impaired debts*/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CL:x42 | boi_CS:x1 | boi_MC:x8 | boi_MC:x914 | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 19.5 | Of which: Guarantees5 and exclusions permitted by Proper Conduct of Banking Business Directive 313 of nonacrruing impaired debts*/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CL:x42 | boi_CS:x1 | boi_MC:x8 | boi_MC:x914 | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 19.6 | Of which: Guarantees5 and exclusions permitted by Proper Conduct of Banking Business Directive 313 of nonacrruing impaired debts*/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | boi_CL:x42 | boi_CS:x2 | boi_MC:x8 | boi_MC:x914 | boi_MU:x1 | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 19.7 | Of which: Guarantees5 and exclusions permitted by Proper Conduct of Banking Business Directive 313 of nonacrruing impaired debts*/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CL:x42 | boi_CS:x2 | boi_MC:x8 | boi_MC:x914 | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 19.8 | Of which: Guarantees5 and exclusions permitted by Proper Conduct of Banking Business Directive 313 of nonacrruing impaired debts*/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | boi_CL:x42 | boi_CS:x2 | boi_MC:x8 | boi_MC:x914 | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 20.1 | Of which: Accruing impaired debts*/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | boi_MC:x962 | boi_MU:x1 | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 20.2 | Of which: Accruing impaired debts*/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | boi_MC:x962 | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 20.3 | Of which: Accruing impaired debts*/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | boi_MC:x962 | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 20.4 | Of which: Accruing impaired debts*/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | boi_MC:x962 | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 20.5 | Of which: Accruing impaired debts*/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | boi_MC:x962 | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 20.6 | Of which: Accruing impaired debts*/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | boi_MC:x962 | boi_MU:x1 | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 20.7 | Of which: Accruing impaired debts*/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | boi_MC:x962 | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 20.8 | Of which: Accruing impaired debts*/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | boi_MC:x962 | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | N/A | N/A |
| 21.1 | Of which: Impaired debts that are not in arrears 90 or more days and are not in a debt restructuring* of problem debt*/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | N/A | boi_ST:x3 | boi_ST:x152 | boi_TI:x94 |
| 21.2 | Of which: Impaired debts that are not in arrears 90 or more days and are not in a debt restructuring* of problem debt*/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | boi_ST:x152 | boi_TI:x94 |
| 21.3 | Of which: Impaired debts that are not in arrears 90 or more days and are not in a debt restructuring* of problem debt*/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | boi_ST:x152 | boi_TI:x94 |
| 21.4 | Of which: Impaired debts that are not in arrears 90 or more days and are not in a debt restructuring* of problem debt*/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | boi_ST:x3 | boi_ST:x152 | boi_TI:x94 |
| 21.5 | Of which: Impaired debts that are not in arrears 90 or more days and are not in a debt restructuring* of problem debt*/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | boi_ST:x3 | boi_ST:x152 | boi_TI:x94 |
| 21.6 | Of which: Impaired debts that are not in arrears 90 or more days and are not in a debt restructuring* of problem debt*/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | N/A | boi_ST:x3 | boi_ST:x152 | boi_TI:x94 |
| 21.7 | Of which: Impaired debts that are not in arrears 90 or more days and are not in a debt restructuring* of problem debt*/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | boi_ST:x152 | boi_TI:x94 |
| 21.8 | Of which: Impaired debts that are not in arrears 90 or more days and are not in a debt restructuring* of problem debt*/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x3 | boi_ST:x152 | boi_TI:x94 |
| 22.1 | Of which: Credit to the public on monitoring list**/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | N/A | boi_ST:x153 | N/A | N/A |
| 22.2 | Of which: Credit to the public on monitoring list**/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x153 | N/A | N/A |
| 22.3 | Of which: Credit to the public on monitoring list**/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x153 | N/A | N/A |
| 22.4 | Of which: Credit to the public on monitoring list**/Annual provision for loan losses | boi_met:md191 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | boi_ST:x153 | N/A | N/A |
| 22.5 | Of which: Credit to the public on monitoring list**/Net annual write-offs | boi_met:md285 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x1 | boi_MC:x8 | N/A | boi_MU:x1 | boi_RP:x28 | boi_SE:x16 | N/A | boi_ST:x153 | N/A | N/A |
| 22.6 | Of which: Credit to the public on monitoring list**/Allowance coefficient1 | boi_met:pd510 | num:percentItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | boi_MU:x1 | N/A | boi_SE:x16 | N/A | boi_ST:x153 | N/A | N/A |
| 22.7 | Of which: Credit to the public on monitoring list**/Recorded debt balance | boi_met:mi468 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x153 | N/A | N/A |
| 22.8 | Of which: Credit to the public on monitoring list**/Balance of credit loss allowance | boi_met:mi3 | xbrli:monetaryItemType | instant | boi_BC:x1 | N/A | N/A | boi_CS:x2 | boi_MC:x8 | N/A | N/A | N/A | boi_SE:x16 | N/A | boi_ST:x153 | N/A | N/A |