Derivative Instruments - Summary of Location and Amount of Gains and Losses of Derivative Contracts (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Unrealized gains (losses)	$ (2)	$ 0
Derivative, Gain (Loss) on Derivative, Net	(70)	$ (16)	$ (16)
Derivative, Gain (Loss) on Derivatives, Total Net	(13)		(93)
Net gains (losses) on derivative contracts [Domain] | Credit Derivatives [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(1)		0
Net gains (losses) on derivative contracts [Domain] | Interest Rate Swap [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(29)		(3)
Net gains (losses) on derivative contracts [Domain] | Futures Contracts [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(40)		(14)
Income Loss On Variable Interest Entities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	57		(77)
Income Loss On Variable Interest Entities [Member] | Interest Rate Swap [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	47		(70)
Income Loss On Variable Interest Entities [Member] | Currency Swaps [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 10		$ (7)