| Net decrease (increase) in due from banks (excluding cash equivalents) | en | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Net decrease (increase) in due from banks (excluding cash equivalents) - OpeCF - BNK | en | http://www.xbrl.org/2003/role/verboseLabel | http://www.xbrl.org/2003/role/link |
| 預け金(現金同等物を除く)の純増(△)減 | ja | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| 預け金(現金同等物を除く)の純増(△)減、営業活動によるキャッシュ・フロー、銀行業 | ja | http://www.xbrl.org/2003/role/verboseLabel | http://www.xbrl.org/2003/role/link |