Fair Value Measurements - Additional Information (Detail) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)		Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)		Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)		Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Loss severity, trust preferred securities					0.85
Average deviation of implied volatility, foreign currency pair					3.00%
Average deviation of implied volatility, at-the-money equity option					5.00%
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					40.00%
Weighted Average [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Inputs, Loss Severity					37.00%
Derivative Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		$ 301	$ 397		$ 301	$ 397
Derivative Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	170	223		170	223
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				$ 49
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		2,172	3,358		2,172	3,358		$ 3,351	3,356	$ 3,323		$ 3,328
Fair value of level 3 liabilities		1,683	2,250		1,683	2,250		1,774	1,906	2,495		2,613
Fair Value Liability, Transfers Into Level 3		(18)	(7)		(23)	(15)
Fair Value Liability, Transfers Out of Level 3		63	143		152	286
Level 3 [Member] | Domestic Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities		1,142	1,677	[1]	1,142	1,677	[1]	1,216	1,407	1,849	[1]	1,867	[1]
Fair Value Liability, Transfers Into Level 3	[1]	(18)	(7)		(21)	(15)
Fair Value Liability, Transfers Out of Level 3		56	82	[1]	102	141	[1]
Level 3 [Member] | Borrowings [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities		541	573	[1]	541	573	[1]	$ 558	$ 499	$ 646	[1]	$ 746	[1]
Fair Value Liability, Transfers Into Level 3		0	0	[1]	(2)	0	[1]
Fair Value Liability, Transfers Out of Level 3		$ 7	$ 61	[1]	$ 50	$ 145	[1]

[1] See Note 9, "Fair Value Option," for additional information. Beginning January 1, 2017, unrealized gains (losses) on fair value option liabilities attributable to credit spread is recorded in other comprehensive income.