Fair Value Measurements - Additional Information (Detail) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)		Jun. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)		Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets		$ 3,301	$ 3,515		$ 3,581	$ 3,301	$ 3,515		$ 3,423	$ 3,504	$ 3,150
Loss severity, trust preferred securities						1.8
Fair Value Assets, Transfers Out of Level 3		(2)	1			$ (2)	101
Fair Value Liability, Transfers Out of Level 3		72	476			283	772
Fair Value Liability, Transfers Into Level 3		45	61			$ 67	110
Average deviation of implied volatility, foreign currency pair						4.00%
Average deviation of implied volatility, at-the-money equity option						7.00%
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						21.00%
Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets		304	466			$ 304	466
Derivative Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets		228	231			228	231
Credit contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of assets	[1]	171	221		257	171	221		$ 179	210	191
Fair Value Assets, Transfers Out of Level 3	[1]	0	0			0	(114)
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		0				$ 121
Fair Value Assets, Transfers Out of Level 3			0		$ 119		119
Domestic Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Liability, Transfers Out of Level 3		54	395	[2]		233	591	[2]
Fair Value Liability, Transfers Into Level 3	[2]	44	59			66	108
Borrowings [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Liability, Transfers Out of Level 3		18	81	[2]		50	181	[2]
Fair Value Liability, Transfers Into Level 3		1	$ 2	[2]		1	$ 2	[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		$ 47				$ 47				$ 50

[1] Level 3 net derivatives included derivative assets of $304 million and derivative liabilities of $228 million as of September 30, 2015 and derivative assets of $466 million and derivative liabilities of $231 million as of September 30, 2014.

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