Derivative Financial Instruments - Additional Information (Detail) - Derivatives, by Derivative Instrument Contract [Domain] - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Derivative Liability, Fair Value, Gross Liability	$ 5,119		$ 5,119		$ 5,577
Derivative Asset, Fair Value, Gross Asset	5,239		5,239		5,839
Cash Flow Hedging
Deferred net gains on derivatives that are recorded in AOCI are expected to be reclassified to net interest income over the next twelve months in connection with the recognition of interest income or interest expense on these hedged items	239		$ 239
written risk participations [Member]
Minimum Term of Credit Risk Derivatives
Maximum Term of Credit Risk Derivatives			8 years
Weighted Average Term of Credit Risk Derivatives
Credit and Market Risk
Derivative asset positions	890		$ 890		1,100
Net derivative asset positions to which the Company was exposed to risk of its counterparties, netted by counterparty where formal netting arrangements exist	1,300		1,300		1,500
Collateral Held by The Company Against Derivative Asset Positions	(472)		(472)		(386)
Adjusted the fair value of its net derivative asset position for estimates of counterparty credit risk	1		1		7
Derivative Liability, Fair Value, Gross Liability	1,100		1,100		$ 1,100
Credit and Market Risk | Additional Termination Event [Member]
Derivative Liability, Fair Value, Gross Liability	8		8
Credit and Market Risk | Additional Termination Event [Member] | Credit Downgrade [Member]
Derivative Liability, Fair Value, Gross Liability	15		15
Credit and Market Risk | Credit Support Annex
Derivative Liability, Fair Value, Gross Liability	1,100		1,100
Derivative Liability, Fair Value of Collateral	1,100		1,100
Credit and Market Risk | Credit Support Annex | Credit Downgrade [Member]
Posted collateral	7		7
Credit Default Swap
Maximum Term of Credit Risk Derivatives					4 years
Maximum exposure					$ 20
Derivative, Notional Amount	279		279		190
Credit Risk Derivatives, at Fair Value, Net	5		5		5
Credit Derivatives Swap Participation
Maximum exposure	35		$ 35		31
Cash Flow Derivatives Hedges [Member]
Derivative, Lower Remaining Maturity Range
Derivative, Higher Remaining Maturity Range			5 years
Weighted Average of Maturities of Cash Flow Hedges
Total Return Swap
Derivative Liability, Fair Value, Gross Liability	13		$ 13		14
Derivative, Notional Amount	2,300		2,300		2,300
Derivative Asset, Fair Value, Gross Asset	17		17		19
Collateral held	409		409		373
Derivatives Sold | Credit Default Swap
Credit Risk Derivatives, at Fair Value, Net	0		0		$ 1
Interest Income (Expense), Net [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ 19	$ 27	$ 38	$ 54