Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018		Mar. 31, 2017	Dec. 31, 2017
Derivative Liability, Fair Value, Gross Liability		$ 3,505			$ 4,442
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net		75
Derivative Asset, Fair Value, Gross Asset		3,074			3,904
Netted counterparty balance [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets		510			541
Derivative Asset, Fair Value of Collateral		426			399
Derivative Credit Risk Valuation Adjustment, Derivative Assets		3			5
Netted counterparty balance gains [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets		936			900
Derivative liability positions containing provisions conditioned on downgrades [Member]
Derivative Liability, Fair Value, Gross Liability		900			1,100
Additional Termination Event [Member]
Derivative Liability, Fair Value, Gross Liability		1
Additional Termination Event [Member] | Maximum [Member]
Derivative Liability, Fair Value, Gross Liability		17
Credit Support Annex [Member]
Derivative Liability, Fair Value, Gross Liability		900
Collateral Already Posted, Aggregate Fair Value		900
Credit Support Annex [Member] | Moody's, Baa2 Rating [Member]
Additional Collateral, Aggregate Fair Value		1
Credit Support Annex [Member] | Moody's, Baa3 Rating [Member]
Additional Collateral, Aggregate Fair Value		4
Credit Default Swap, Buying Protection [Member]
Derivative, Notional Amount					5
Total Return Swap [Member]
Derivative Liability, Fair Value, Gross Liability		19			13
Collateral Already Posted, Aggregate Fair Value		372			368
Derivative, Notional Amount		1,700			1,700
Derivative Asset, Fair Value, Gross Asset		$ 22			15
Financial Guarantee [Member]
Derivative, Average Remaining Maturity		4 years 8 months		5 years 6 months
Credit Derivative, Maximum Exposure, Undiscounted		$ 85			55
Financial Guarantee [Member] | Minimum [Member]
Derivative, Remaining Maturity		1 year		1 year
Financial Guarantee [Member] | Maximum [Member]
Derivative, Remaining Maturity		8 years		9 years
Interest Rate Contract [Member] | Cash Flow Hedging [Member]
Derivative Liability, Fair Value, Gross Liability		$ 0	[1]		252	[2]
Derivative, Average Remaining Maturity		3 years 7 months		3 years 7 months
Derivative Asset, Fair Value, Gross Asset		$ 2	[1]		$ 2	[2]
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		5 years		5 years
Interest Income [Member] | Loans Held-For-Investment [Member] | Interest Rate Contract [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	[3]	$ (165)		$ (25)

[1] See “Cash Flow Hedges” in this Note for further discussion.

[2] See “Cash Flow Hedges” in this Note for further discussion.

[3] During the three months ended March 31, 2017, the Company also reclassified $18 million of pre-tax gains from AOCI into Net interest income relating to hedging relationships that have been terminated and are reclassified into earnings consistent with the pattern of net cash flows expected to be recognized.