Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Derivative Liability, Fair Value, Gross Liability	$ 4,930	$ 5,577
Derivative Asset, Fair Value, Gross Asset	5,258	5,839
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	211
Derivative Asset, Notional Amount	140,073	118,139
Derivative Liability, Notional Amount	109,543	114,144
Netted counterparty balance [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets	1,100	1,100
Derivative Asset, Fair Value of Collateral	(592)	386
Derivative Credit Risk Valuation Adjustment, Derivative Assets	5	7
Derivative liability positions containing provisions conditioned on downgrades [Member]
Derivative Liability, Fair Value, Gross Liability	1,100	1,092
Netted counterparty balance gains [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets	1,700	$ 1,500
Additional Termination Event [Member]
Derivative Liability, Fair Value, Gross Liability	1
Credit Support Annex
Derivative Liability, Fair Value, Gross Liability	1,100
Collateral Already Posted, Aggregate Fair Value	1,100
Additional Collateral, Aggregate Fair Value	$ 7
Credit Default Swap, Selling Protection [Member]
Maximum Term of Credit Risk Derivatives	5 years	4 years
Credit Derivative, Maximum Exposure, Undiscounted	$ 150	$ 20
Credit Risk Derivatives, at Fair Value, Net	1	1
Credit Default Swap, Buying Protection [Member]
Derivative, Notional Amount	315	190
Credit Risk Derivatives, at Fair Value, Net	2	5
Total Return Swap
Derivative Liability, Fair Value, Gross Liability	11	14
Collateral Already Posted, Aggregate Fair Value	462	373
Derivative, Notional Amount	2,400	2,300
Derivative Asset, Fair Value, Gross Asset	16	19
Financial Guarantee [Member]
Credit Derivative, Maximum Exposure, Undiscounted	$ 73	$ 31
Derivative, Lower Remaining Maturity Range	0 years
Derivative, Higher Remaining Maturity Range	8 years
Weighted Average of Maturities of Cash Flow Hedges	4 years
Interest Rate Contract [Member] | Cash Flow Hedging [Member]
Derivative, Lower Remaining Maturity Range	1 year
Derivative, Higher Remaining Maturity Range	7 years
Weighted Average of Maturities of Cash Flow Hedges	3 years 2 months
Maximum [Member] | Additional Termination Event [Member]
Derivative Liability, Fair Value, Gross Liability	$ 15