| r0.1 | label_boi_a2/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | N/A | N/A | N/A | boi_RP:x19 |
| r0.2 | label_boi_a2/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | N/A | boi_MU:x1 | N/A | boi_RP:x19 |
| r1.1 | B. Non-interest financing income in respect of trading activities/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | N/A | N/A | boi_PL:x2 | boi_RP:x19 |
| r1.2 | B. Non-interest financing income in respect of trading activities/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | N/A | boi_CS:x2 | N/A | N/A | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 1.1 | Net income (expenses) in respect of other derivative instruments/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | boi_PL:x2 | boi_RP:x19 |
| 1.2 | Net income (expenses) in respect of other derivative instruments/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 2.1 | Net realized and unrealized gains from adjustments to fair value of bond held for trading/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x130 | boi_MC:x15 | N/A | boi_PL:x2 | boi_RP:x19 |
| 2.2 | Net realized and unrealized gains from adjustments to fair value of bond held for trading/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x130 | boi_MC:x15 | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 3.1 | Of which: Share of gains (losses) related to trading bonds held on balance-sheet date/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x134 | boi_MC:x15 | N/A | boi_PL:x2 | boi_RP:x19 |
| 3.2 | Of which: Share of gains (losses) related to trading bonds held on balance-sheet date/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x134 | boi_MC:x15 | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 4.1 | Net realized and unutilized gains from adjustments to fair value of shares held for trading/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x130 | boi_MC:x30 | N/A | boi_PL:x2 | boi_RP:x19 |
| 4.2 | Net realized and unutilized gains from adjustments to fair value of shares held for trading/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x130 | boi_MC:x30 | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 5.1 | Of which: Share of gain (loss) related to trading bonds held on balance-sheet date/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x134 | boi_MC:x30 | N/A | boi_PL:x2 | boi_RP:x19 |
| 5.2 | Of which: Share of gain (loss) related to trading bonds held on balance-sheet date/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x134 | boi_MC:x30 | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 6.1 | Dividends received from trading activities/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x2 | N/A | boi_MC:x137 | N/A | N/A | boi_PL:x2 | boi_RP:x19 |
| 6.2 | Dividends received from trading activities/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x9 | boi_CS:x2 | N/A | boi_MC:x137 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 7.1 | Total from trading activities/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x128 | N/A | N/A | boi_PL:x2 | boi_RP:x19 |
| 7.2 | Total from trading activities/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| r9.1 | Details of non-interest financing income in respect of trading activities, by interest exposure/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x128 | N/A | N/A | boi_PL:x2 | boi_RP:x19 |
| r9.2 | Details of non-interest financing income in respect of trading activities, by interest exposure/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 8.1 | Interest-rate exposure/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x22 | boi_MC:x128 | N/A | N/A | boi_PL:x2 | boi_RP:x19 |
| 8.2 | Interest-rate exposure/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x22 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 9.1 | Foreign-currency exposure/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x23 | boi_MC:x128 | N/A | N/A | boi_PL:x2 | boi_RP:x19 |
| 9.2 | Foreign-currency exposure/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x23 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 10.1 | Exposure to shares/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x24 | boi_MC:x128 | N/A | N/A | boi_PL:x2 | boi_RP:x19 |
| 10.2 | Exposure to shares/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x24 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 11.1 | Exposure to commodities and other/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x25 | boi_MC:x128 | N/A | N/A | boi_PL:x2 | boi_RP:x19 |
| 11.2 | Exposure to commodities and other/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | boi_EC:x25 | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| 12.1 | Total/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x128 | N/A | N/A | boi_PL:x2 | boi_RP:x19 |
| 12.2 | Total/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x128 | N/A | boi_MU:x1 | boi_PL:x2 | boi_RP:x19 |
| r15.1 | C. Ineffective part of hedging relations - additional details/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | N/A | boi_RP:x19 |
| r15.2 | C. Ineffective part of hedging relations - additional details/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | N/A | boi_RP:x19 |
| r16.1 | Fair value hedges/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | N/A | boi_RP:x19 |
| r16.2 | Fair value hedges/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | N/A | boi_RP:x19 |
| 13.1 | Ineffectiveness of hedges/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | boi_PL:x20 | boi_RP:x19 |
| 13.2 | Ineffectiveness of hedges/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x20 | boi_RP:x19 |
| 14.1 | Profit (loss) component removed for purpose of assessing effectiveness of the hedging/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | boi_PL:x21 | boi_RP:x19 |
| 14.2 | Profit (loss) component removed for purpose of assessing effectiveness of the hedging/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x21 | boi_RP:x19 |
| 15.1 | Net profits (losses) in respect of resilient engagement no longer suitable as fair value hedge/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | boi_PL:x22 | boi_RP:x19 |
| 15.2 | Net profits (losses) in respect of resilient engagement no longer suitable as fair value hedge/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x22 | boi_RP:x19 |
| r20.1 | Cash flow hedges/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | N/A | boi_RP:x19 |
| r20.2 | Cash flow hedges/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | N/A | boi_RP:x19 |
| 16.1 | Ineffectivness of hedge/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | boi_PL:x23 | boi_RP:x19 |
| 16.2 | Ineffectivness of hedge/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x23 | boi_RP:x19 |
| 17.1 | Profit (loss) component removed for purpose of assessing effectiveness of the hedging/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | boi_PL:x24 | boi_RP:x19 |
| 17.2 | Profit (loss) component removed for purpose of assessing effectiveness of the hedging/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x24 | boi_RP:x19 |
| 18.1 | Profits (losses) that were reclassified because the transactions were apparently not conducted/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | boi_PL:x25 | boi_RP:x19 |
| 18.2 | Profits (losses) that were reclassified because the transactions were apparently not conducted/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x25 | boi_RP:x19 |
| 19.1 | Total/Quarter (Year -1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | N/A | boi_PL:x19 | boi_RP:x19 |
| 19.2 | Total/Accumulated from the beginning of year (-1) | boi_met:md13 | xbrli:monetaryItemType | instant | boi_BC:x11 | boi_CS:x2 | N/A | boi_MC:x127 | boi_MC:x18 | boi_MU:x1 | boi_PL:x19 | boi_RP:x19 |