Commitments, Contingencies and Guarantees - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Summary Of Commitments And Contingent Liabilities [Line Items]
Approximate amount of lending commitments held for investment	$ 100,790,000,000		$ 98,050,000,000
Approximate amount of lending commitments held for sale	7,650,000,000		6,870,000,000
Notional amount of loan commitments which are protected by SMFG against credit loss	$ 26,760,000,000		$ 26,880,000,000
Credit loss protection percentage of first loss on loan commitments provided by SMFG	95.00%
Approximate amount of maximum protection of first loss on loan commitments provided by SMFG	$ 950,000,000
SMFG credit loss protection for additional losses percentage	70.00%		70.00%
Maximum protection on additional losses on loan commitments provided by SMFG	$ 1,130,000,000		$ 1,130,000,000
Protection provided by SMFG for additional losses	768,000,000		768,000,000
Commitments to invest in funds managed by the firm	$ 2,130,000,000		2,100,000,000
The latest year through which the firm's noncancelable lease agreements extend	2069
Operating Leases, Rent Expense	$ 70,000,000	$ 62,000,000
Amount of loans sold to government sponsored enterprises during the period 2005 through 2008	10,000,000,000
Amount of loans sold to other third parties during the period 2005 through 2008	11,000,000,000
Outstanding balance for loans transferred to trusts and other mortgage securitization vehicles during the period 2005 through 2008	125,000,000,000
Collateral held by lenders in connection with securities lending indemnifications	40,110,000,000		$ 34,330,000,000
Residential Mortgage Backed Securities Working Group [Member]
Summary Of Commitments And Contingent Liabilities [Line Items]
Settlement agreement amount	$ 1,800,000,000