Fair Value Measurements - Additional Information (Detail) - Valuation Technique [Domain] $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)		Jun. 30, 2015 USD ($)		Jun. 30, 2014 USD ($)		Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets		$ 3,423	$ 3,581		$ 3,423		$ 3,581		$ 3,497	$ 3,504	$ 3,690	$ 3,150
Loss severity, trust preferred securities					1.8
Fair Value Liability, Transfers Out of Level 3		90	131		$ 211		342
Fair Value Liability, Transfers Into Level 3		(22)	(27)		$ (22)		(95)
Average deviation of implied volatility, foreign currency pair					6.00%
Average deviation of implied volatility, at-the-money equity option					5.00%
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					68.00%
Weighted Average [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Inputs, Loss Severity					7.00%
Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets		387	538		$ 387		538
Derivative Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets		217	222		217		222
Credit contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets	[1]	179	257		179		257		$ 192	210	181	191
Government debt securities issued by foreign entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets			0				0				$ 117	$ 121
Deposits in domestic offices [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Liability, Transfers Out of Level 3		78	104	[2]	179		244	[2]
Fair Value Liability, Transfers Into Level 3		(22)	$ (27)	[2]	(22)	[2]	$ (95)	[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			$ 52					$ 50

[1] Level 3 net derivatives included derivative assets of $387 million and derivative liabilities of $217 million as of June 30, 2015 and derivative assets of $538 million and derivative liabilities of $222 million as of June 30, 2014.

[2] See Note 10, "Fair Value Option," for additional information.