Derivative instruments and hedging activities - Additional Information (Detail) - JPY (¥) ¥ in Billions	Mar. 31, 2016	Mar. 31, 2015
Derivative instruments and hedging activities
Derivative liability position with credit-risk-related contingent features	¥ 719	¥ 874
Collateral pledged for derivative instruments with credit-risk-related contingent features that are in a liability position	587	708
Additional collateral required to be posted, aggregate fair value	¥ 15	¥ 19

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624258-113959

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