Credit Quality of Financing Receivables and the Allowance for Credit Losses - Additional Information (Detail) ¥ in Millions	Mar. 31, 2018 JPY (¥) Property	Mar. 31, 2017 JPY (¥) Property
Receivables [Abstract]
Number of foreclosed residential real estate properties \| Property	0	0
Residential mortgage loans in process of foreclosure \| ¥	¥ 245	¥ 324

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL49126937-111524

Name:	us-gaap_MortgageLoansInProcessOfForeclosureAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant