Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 218
Derivative Asset, Notional Amount	143,941		$ 123,257
Derivative Liability, Notional Amount	117,939		124,755
Netted counterparty balance [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets	1,300		896
Derivative Asset, Fair Value of Collateral	710		463
Derivative Credit Risk Valuation Adjustment, Derivative Assets	6		4
Derivative liability positions containing provisions conditioned on downgrades [Member]
Derivative Liability, Fair Value, Gross Liability	1,300		1,100
Netted counterparty balance gains [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets	2,000		1,400
Additional Termination Event [Member]
Derivative Liability, Fair Value, Gross Liability	1
Credit Support Annex
Derivative Liability, Fair Value, Gross Liability	1,300
Collateral Already Posted, Aggregate Fair Value	1,300
Additional Collateral, Aggregate Fair Value	7
Credit Default Swap, Selling Protection [Member]
Credit Derivative, Maximum Exposure, Undiscounted	0		0
Credit Risk Derivatives, at Fair Value, Net	0		0
Credit Default Swap, Buying Protection [Member]
Derivative, Notional Amount	185		150
Credit Risk Derivatives, at Fair Value, Net	2		1
Total Return Swap [Member]
Derivative Liability, Fair Value, Gross Liability	26		52
Collateral Already Posted, Aggregate Fair Value	508		492
Derivative, Notional Amount	2,200		2,200
Derivative Asset, Fair Value, Gross Asset	31		57
Financial Guarantee [Member]
Credit Derivative, Maximum Exposure, Undiscounted	$ 74		$ 55
Derivative, Lower Remaining Maturity Range	0 years	1 year
Derivative, Higher Remaining Maturity Range	10 years	8 years
Weighted Average of Maturities of Cash Flow Hedges	5 years 9 months	5 years 7 months
Interest Rate Contract [Member] | Cash Flow Hedging [Member]
Derivative, Lower Remaining Maturity Range	1 year	1 year
Derivative, Higher Remaining Maturity Range	7 years	7 years
Weighted Average of Maturities of Cash Flow Hedges	3 years 2 months	3 years 3 months
Maximum [Member] | Additional Termination Event [Member]
Derivative Liability, Fair Value, Gross Liability	$ 18