Fair Value Measurements - Additional Information (Detail) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)		Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)		Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)		Dec. 31, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		$ 3,288	$ 3,301		$ 3,288	$ 3,301		$ 3,358	$ 3,328	$ 3,423		$ 3,504
Fair value of level 3 liabilities		1,917	2,499		$ 1,917	2,499		2,250	2,613	2,479		2,615
Loss severity, trust preferred securities					1.8
Average deviation of implied volatility, foreign currency pair					4.00%
Average deviation of implied volatility, at-the-money equity option					5.00%
Fair Value Assets, Transfers Into Level 3		(1)	0		$ 0	0
Fair Value Assets, Transfers Out of Level 3		(92)	2		(92)	2
Fair Value Liability, Transfers Into Level 3		(39)	(45)		(54)	(67)
Fair Value Liability, Transfers Out of Level 3		124	72		$ 411	283
Revaluation period					45 days
Weighted Average [Member] | Residential mortgages and home equity mortgages [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Inputs, Loss Severity					52.00%
Weighted Average [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Inputs, Loss Severity					34.00%
Derivative Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		335	304		$ 335	304
Derivative Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	122	228		122	228
Credit contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets	[2]	207	171		207	171		188	179	179		210
Fair Value Assets, Transfers Into Level 3	[2]	0	0		0	0
Fair Value Assets, Transfers Out of Level 3	[2]	0	0		0	0
Mortgage servicing rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets	[3]	0	130		0	130		104	140	158		159
Fair Value Assets, Transfers Into Level 3	[3]	0	0		0	0
Fair Value Assets, Transfers Out of Level 3	[3]	(95)	0		(95)	0
Domestic Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities		1,404	1,754	[1]	1,404	1,754	[1]	1,677	1,867	1,817	[1]	1,968	[1]
Fair Value Liability, Transfers Into Level 3	[1]	(39)	(44)		(54)	(66)
Fair Value Liability, Transfers Out of Level 3		57	54	[1]	198	233	[1]
Borrowings [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities		513	745	[1]	513	745	[1]	$ 573	746	$ 662	[1]	$ 647	[1]
Fair Value Liability, Transfers Into Level 3		0	(1)	[1]	0	(1)	[1]
Fair Value Liability, Transfers Out of Level 3		67	$ 18	[1]	213	$ 50	[1]
Other liabilities [Member] | Standby Letters of Credit [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees on standby letters of credit		$ 49			$ 49				$ 54

[1] See Note 11, "Fair Value Option," for additional information.

[2] Level 3 net derivatives included derivative assets of $335 million and derivative liabilities of $122 million at September 30, 2016 and derivative assets of $304 million and derivative liabilities of $228 million at September 30, 2015.

[3] See Note 7, "Intangible Assets," and Note 9, "Other Assets Held for Sale," for additional information.