| r0.1 | label_boi_a2/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| r0.2 | label_boi_a2/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| r0.3 | label_boi_a2/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| r0.4 | label_boi_a2/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| r0.5 | label_boi_a2/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| r0.6 | label_boi_a2/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| r0.7 | label_boi_a2/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| r0.8 | label_boi_a2/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| r0.9 | label_boi_a2/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| r0.10 | label_boi_a2/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | N/A | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| r1.1 | Financial assets:/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| r1.2 | Financial assets:/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| r1.3 | Financial assets:/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| r1.4 | Financial assets:/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| r1.5 | Financial assets:/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| r1.6 | Financial assets:/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| r1.7 | Financial assets:/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| r1.8 | Financial assets:/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| r1.9 | Financial assets:/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| r1.10 | Financial assets:/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 1.1 | Cash and deposits in banks/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x33 |
| 1.2 | Cash and deposits in banks/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x17 |
| 1.3 | Cash and deposits in banks/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x18 |
| 1.4 | Cash and deposits in banks/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x20 |
| 1.5 | Cash and deposits in banks/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x21 |
| 1.6 | Cash and deposits in banks/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x22 |
| 1.7 | Cash and deposits in banks/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x23 |
| 1.8 | Cash and deposits in banks/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x1 | N/A |
| 1.9 | Cash and deposits in banks/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x1 | N/A |
| 1.10 | Cash and deposits in banks/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x949 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x1 | N/A |
| 2.1 | Bonds held to maturity/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 2.2 | Bonds held to maturity/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 2.3 | Bonds held to maturity/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 2.4 | Bonds held to maturity/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 2.5 | Bonds held to maturity/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 2.6 | Bonds held to maturity/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 2.7 | Bonds held to maturity/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 2.8 | Bonds held to maturity/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 2.9 | Bonds held to maturity/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 2.10 | Bonds held to maturity/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x5 | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 3.1 | Bonds available for sale/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 3.2 | Bonds available for sale/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 3.3 | Bonds available for sale/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 3.4 | Bonds available for sale/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 3.5 | Bonds available for sale/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 3.6 | Bonds available for sale/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 3.7 | Bonds available for sale/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 3.8 | Bonds available for sale/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 3.9 | Bonds available for sale/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 3.10 | Bonds available for sale/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x1 | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 4.1 | Bonds for trading/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 4.2 | Bonds for trading/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 4.3 | Bonds for trading/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 4.4 | Bonds for trading/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 4.5 | Bonds for trading/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 4.6 | Bonds for trading/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 4.7 | Bonds for trading/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 4.8 | Bonds for trading/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 4.9 | Bonds for trading/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 4.10 | Bonds for trading/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | boi_PL:x2 | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 5.1 | Securities borrowed or purchased under agreements to resell/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 5.2 | Securities borrowed or purchased under agreements to resell/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 5.3 | Securities borrowed or purchased under agreements to resell/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 5.4 | Securities borrowed or purchased under agreements to resell/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 5.5 | Securities borrowed or purchased under agreements to resell/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 5.6 | Securities borrowed or purchased under agreements to resell/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 5.7 | Securities borrowed or purchased under agreements to resell/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 5.8 | Securities borrowed or purchased under agreements to resell/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 5.9 | Securities borrowed or purchased under agreements to resell/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 5.10 | Securities borrowed or purchased under agreements to resell/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 6.1 | Credit to the public,net/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x33 |
| 6.2 | Credit to the public,net/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x17 |
| 6.3 | Credit to the public,net/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x18 |
| 6.4 | Credit to the public,net/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x20 |
| 6.5 | Credit to the public,net/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x21 |
| 6.6 | Credit to the public,net/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x22 |
| 6.7 | Credit to the public,net/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x23 |
| 6.8 | Credit to the public,net/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x16 | N/A |
| 6.9 | Credit to the public,net/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x16 | N/A |
| 6.10 | Credit to the public,net/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x16 | N/A |
| 7.1 | Credit to the government/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x33 |
| 7.2 | Credit to the government/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x17 |
| 7.3 | Credit to the government/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x18 |
| 7.4 | Credit to the government/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x20 |
| 7.5 | Credit to the government/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x21 |
| 7.6 | Credit to the government/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x22 |
| 7.7 | Credit to the government/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x23 |
| 7.8 | Credit to the government/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x11 | N/A |
| 7.9 | Credit to the government/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x11 | N/A |
| 7.10 | Credit to the government/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x950 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x11 | N/A |
| 8.1 | Other assets/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 8.2 | Other assets/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 8.3 | Other assets/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 8.4 | Other assets/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 8.5 | Other assets/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 8.6 | Other assets/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 8.7 | Other assets/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 8.8 | Other assets/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 8.9 | Other assets/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 8.10 | Other assets/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x953 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 9.1 | Total financial assets/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 9.2 | Total financial assets/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 9.3 | Total financial assets/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 9.4 | Total financial assets/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 9.5 | Total financial assets/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 9.6 | Total financial assets/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 9.7 | Total financial assets/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 9.8 | Total financial assets/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 9.9 | Total financial assets/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 9.10 | Total financial assets/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x1 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x948 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| r11.1 | Financial liabilities/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| r11.2 | Financial liabilities/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| r11.3 | Financial liabilities/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| r11.4 | Financial liabilities/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| r11.5 | Financial liabilities/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| r11.6 | Financial liabilities/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| r11.7 | Financial liabilities/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| r11.8 | Financial liabilities/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| r11.9 | Financial liabilities/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| r11.10 | Financial liabilities/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | N/A | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 10.1 | Public deposits/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x33 |
| 10.2 | Public deposits/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x17 |
| 10.3 | Public deposits/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x18 |
| 10.4 | Public deposits/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x20 |
| 10.5 | Public deposits/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x21 |
| 10.6 | Public deposits/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x22 |
| 10.7 | Public deposits/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x16 | boi_TI:x23 |
| 10.8 | Public deposits/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x16 | N/A |
| 10.9 | Public deposits/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x16 | N/A |
| 10.10 | Public deposits/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x16 | N/A |
| 11.1 | Deposits from banks/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x33 |
| 11.2 | Deposits from banks/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x17 |
| 11.3 | Deposits from banks/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x18 |
| 11.4 | Deposits from banks/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x20 |
| 11.5 | Deposits from banks/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x21 |
| 11.6 | Deposits from banks/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x22 |
| 11.7 | Deposits from banks/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x1 | boi_TI:x23 |
| 11.8 | Deposits from banks/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x1 | N/A |
| 11.9 | Deposits from banks/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x1 | N/A |
| 11.10 | Deposits from banks/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x1 | N/A |
| 12.1 | Government deposits/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x33 |
| 12.2 | Government deposits/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x17 |
| 12.3 | Government deposits/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x18 |
| 12.4 | Government deposits/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x20 |
| 12.5 | Government deposits/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x21 |
| 12.6 | Government deposits/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x22 |
| 12.7 | Government deposits/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | N/A | boi_SE:x11 | boi_TI:x23 |
| 12.8 | Government deposits/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x11 | N/A |
| 12.9 | Government deposits/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x11 | N/A |
| 12.10 | Government deposits/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x957 | N/A | boi_PL:x9 | boi_RP:x24 | boi_SE:x11 | N/A |
| 13.1 | Securities borrowed or purchased under agreements to resell/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 13.2 | Securities borrowed or purchased under agreements to resell/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 13.3 | Securities borrowed or purchased under agreements to resell/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 13.4 | Securities borrowed or purchased under agreements to resell/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 13.5 | Securities borrowed or purchased under agreements to resell/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 13.6 | Securities borrowed or purchased under agreements to resell/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 13.7 | Securities borrowed or purchased under agreements to resell/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 13.8 | Securities borrowed or purchased under agreements to resell/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 13.9 | Securities borrowed or purchased under agreements to resell/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 13.10 | Securities borrowed or purchased under agreements to resell/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x952 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 14.1 | Bonds and subordinated notes/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 14.2 | Bonds and subordinated notes/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 14.3 | Bonds and subordinated notes/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 14.4 | Bonds and subordinated notes/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 14.5 | Bonds and subordinated notes/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 14.6 | Bonds and subordinated notes/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 14.7 | Bonds and subordinated notes/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 14.8 | Bonds and subordinated notes/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 14.9 | Bonds and subordinated notes/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 14.10 | Bonds and subordinated notes/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x951 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 15.1 | Other liabilities/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 15.2 | Other liabilities/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 15.3 | Other liabilities/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 15.4 | Other liabilities/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 15.5 | Other liabilities/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 15.6 | Other liabilities/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 15.7 | Other liabilities/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 15.8 | Other liabilities/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 15.9 | Other liabilities/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 15.10 | Other liabilities/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x958 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 16.1 | Total financial liabilities/Up to one year | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x33 |
| 16.2 | Total financial liabilities/Over one year to three years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x17 |
| 16.3 | Total financial liabilities/Over three years to five years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x18 |
| 16.4 | Total financial liabilities/Over five years to ten years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x20 |
| 16.5 | Total financial liabilities/Over ten years to twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x21 |
| 16.6 | Total financial liabilities/Over twenty years | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x22 |
| 16.7 | Total financial liabilities/Without fixed maturity | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | N/A | N/A | boi_TI:x23 |
| 16.8 | Total financial liabilities/Total fair value | boi_met:mi5 | xbrli:monetaryItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 16.9 | Total financial liabilities/Internal rate of return | boi_met:pi11 | num:percentItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |
| 16.10 | Total financial liabilities/Average duration | boi_met:ri12 | xbrli:decimalItemType | instant | boi_BC:x2 | boi_CS:x2 | boi_CU:x6 | boi_FN:x1 | boi_MC:x960 | N/A | boi_PL:x9 | boi_RP:x24 | N/A | N/A |