Fair Value Measurements - Additional Information (Detail) $ in Millions		3 Months Ended
		Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)		Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets		$ 3,323	$ 3,498		$ 3,328	$ 3,504
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		6.00%
Fair Value Liability, Transfers Out of Level 3		$ 139	121
Fair Value Liability, Transfers Into Level 3		(8)	0
Fair Value Assets, Transfers Out of Level 3		$ 1	1
Revaluation period		45 days
Weighted Average [Member] | Residential Mortgage [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Inputs, Loss Severity		75.00%
Weighted Average [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Inputs, Loss Severity		36.00%
Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets		$ 391	463
Derivative Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets		268	208
Credit contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets	[1]	177	192		179	$ 210
Fair Value Assets, Transfers Out of Level 3	[1]	0	0
Domestic Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Liability, Transfers Out of Level 3		55	101	[2]
Fair Value Liability, Transfers Into Level 3	[2]	(8)	0
Borrowings [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Liability, Transfers Out of Level 3		84	20	[2]
Fair Value Liability, Transfers Into Level 3		0	$ 0	[2]
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		$ 52			$ 54

[1] Level 3 net derivatives included derivative assets of $391 million and derivative liabilities of $268 million as of March 31, 2016 and derivative assets of $463 million and derivative liabilities of $208 million as of March 31, 2015.

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