Derivative instruments and hedging activities - Concentration of exposures to credit risk in OTC derivatives with financial institutions (Detail) - JPY (¥) ¥ in Billions	Mar. 31, 2020	Mar. 31, 2019
Derivative [Line Items]
Gross fair value of derivative assets	¥ 21,190	¥ 14,929
Financial institutions [Member]
Derivative [Line Items]
Gross fair value of derivative assets	17,711	13,332
Impact of master netting agreements	(15,479)	(11,602)
Impact of collateral	(1,707)	(1,507)
Net exposure to credit risk	¥ 525	¥ 223

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant