Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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Maximum potential amount of future undiscounted payments that could be required under the credit derivative, before reduction for potential recoveries under recourse or collateralization provisions.

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Fair value of securities received as collateral against derivative assets.

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Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivative Liability, Fair Value, Gross Liability	$ 3,829		$ 3,829		$ 4,442
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	135		135
Derivative, Notional Amount	232,120		232,120		249,705
Derivative Asset, Fair Value, Gross Asset	3,278		3,278		3,904
Netted counterparty balance [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets	404		404		541
Derivative Asset, Fair Value of Collateral	485		485		399
Netted counterparty balance gains [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets	889		889		900
Derivative liability positions containing provisions conditioned on downgrades [Member]
Derivative Liability, Fair Value, Gross Liability	1,000		1,000		1,100
Additional Termination Event [Member]
Derivative Liability, Fair Value, Gross Liability	1		1
Additional Termination Event [Member] \| Maximum [Member]
Derivative Liability, Fair Value, Gross Liability	18		18
Credit Support Annex [Member]
Derivative Liability, Fair Value, Gross Liability	1,000		1,000
Collateral Already Posted, Aggregate Fair Value	900		900
Credit Support Annex [Member] \| Moody's, Baa2 Rating [Member]
Additional Collateral, Aggregate Fair Value	2		2
Credit Support Annex [Member] \| Moody's, Baa3 Rating [Member]
Additional Collateral, Aggregate Fair Value	3		3
Credit Support Annex [Member] \| Moody's, Ba1 Rating [Member]
Additional Collateral, Aggregate Fair Value	2		2
Credit Default Swap, Buying Protection [Member]
Derivative, Notional Amount					5
Total Return Swap [Member]
Derivative Liability, Fair Value, Gross Liability	23		23		13
Collateral Already Posted, Aggregate Fair Value	486		486		368
Derivative, Notional Amount	1,900		1,900		1,700
Derivative Asset, Fair Value, Gross Asset	25		$ 25		15
Financial Guarantee [Member]
Derivative, Average Remaining Maturity			6 years 5 months	5 years 6 months
Credit Derivative, Maximum Exposure, Undiscounted	230		$ 230		$ 55
Financial Guarantee [Member] \| Minimum [Member]
Derivative, Remaining Maturity			1 year	1 year
Financial Guarantee [Member] \| Maximum [Member]
Derivative, Remaining Maturity			11 years	9 years
Interest Rate Contract [Member] \| Cash Flow Hedging [Member]
Derivative, Average Remaining Maturity			3 years 1 month	3 years 7 months
Interest Rate Contract [Member] \| Minimum [Member] \| Cash Flow Hedging [Member]
Derivative, Remaining Maturity			1 year	1 year
Interest Rate Contract [Member] \| Maximum [Member] \| Cash Flow Hedging [Member]
Derivative, Remaining Maturity			7 years	5 years
Interest Income [Member] \| Loans Held-For-Investment [Member] \| Interest Rate Contract [Member] \| Cash Flow Hedging [Member]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	$ (48)	$ 10	$ (274)	$ 61