Commitments, Contingencies and Guarantees - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Approximate amount of lending commitments held for investment	$ 91,150,000,000		$ 91,150,000,000		$ 93,920,000,000
Approximate amount of lending commitments held for sale	17,460,000,000		17,460,000,000		9,920,000,000
Notional amount of loan commitments which are protected by SMFG against credit loss	$ 27,440,000,000		$ 27,440,000,000		27,030,000,000
Credit loss protection percentage of first loss on loan commitments provided by SMFG	95.00%		95.00%
Approximate amount of maximum protection of first loss on loan commitments provided by SMFG	$ 950,000,000		$ 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		768,000,000
Commitments to invest in funds managed by the firm	2,020,000,000		$ 2,020,000,000		2,860,000,000
The latest year through which the firm's noncancelable lease agreements extend			2069
Operating Leases, Rent Expense	65,000,000	$ 63,000,000	$ 187,000,000	$ 190,000,000
Exit costs incurred	(63,000,000)		(63,000,000)
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		125,000,000,000
Collateral held by lenders in connection with securities lending indemnifications	$ 39,530,000,000		$ 39,530,000,000		$ 32,850,000,000