| Loss on foreign exchange transactions | en | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Loss on foreign exchange transactions-OE-BNK | en | http://www.xbrl.org/2003/role/verboseLabel | http://www.xbrl.org/2003/role/link |
| Loss on foreign exchange transactions | en | http://disclosure.edinet-fsa.go.jp/jppfs/bnk/role/label | http://www.xbrl.org/2003/role/link |
| 外国為替売買損 | ja | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| 外国為替売買損、経常費用、銀行業 | ja | http://www.xbrl.org/2003/role/verboseLabel | http://www.xbrl.org/2003/role/link |
| (うち外国為替売買損) | ja | http://disclosure.edinet-fsa.go.jp/jppfs/bnk/role/label | http://www.xbrl.org/2003/role/link |