Fair Value Measurements - Additional Information (Detail) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 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				2.00%
Average deviation of implied volatility, at-the-money equity option				5.00%
Revaluation period				45 days
Derivative Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		$ 294	$ 335	$ 294	$ 335
Derivative Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	169	122	$ 169	122
Residential Mortgage [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Inputs, Loss Severity				57.00%
Impaired commercial loans [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Inputs, Loss Severity				34.00%
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		50		$ 50			$ 49
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		2,178	3,288	2,178	3,288	$ 2,172	3,356	$ 3,358	$ 3,328
Fair value of level 3 liabilities		1,498	1,917	1,498	1,917	1,683	1,906	2,250	2,613
Fair Value Liability, Transfers Into Level 3		(4)	(39)	(27)	(54)
Fair Value Liability, Transfers Out of Level 3		109	124	261	411
Fair Value Assets, Transfers Out of Level 3		(2)	(92)	1	(92)
Level 3 [Member] | Mortgage servicing rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets	[2],[3]		0		0			104	140
Fair Value Assets, Transfers Out of Level 3	[2],[3]		(95)		(95)
Level 3 [Member] | Domestic Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	945	1,404	945	1,404	1,142	1,407	1,677	1,867
Fair Value Liability, Transfers Into Level 3	[1]	(4)	(39)	(25)	(54)
Fair Value Liability, Transfers Out of Level 3	[1]	82	57	184	198
Level 3 [Member] | Borrowings [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	553	513	553	513	$ 541	$ 499	$ 573	$ 746
Fair Value Liability, Transfers Into Level 3	[1]	0	0	(2)	0
Fair Value Liability, Transfers Out of Level 3	[1]	$ 27	$ 67	$ 77	$ 213

[1] See Note 10, "Fair Value Option," for additional information. Beginning January 1, 2017, unrealized gains (losses) on fair value option liabilities attributable to our own credit spread is recorded in other comprehensive income (loss).

[2] During the fourth quarter of 2016, we sold our remaining residential mortgage servicing rights portfolio to a third party. Gains (losses) on residential mortgage servicing rights were included in residential mortgage banking revenue (expense) in the consolidated statement of income.

[3] Realized gains (losses) on securities available-for-sale are included in other securities gains, net in the consolidated statement income. Unrealized gains (losses) on securities available-for-sale are included in other comprehensive income (loss).