Derivative Instruments - Summary of Location and Amount of Gains and Losses of Derivative Contracts (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Unrealized Gain (Loss) on Derivatives									$ 1	$ (1)	$ 15
Derivative, Gain (Loss) on Derivative, Net	$ 12	$ (10)	$ (35)	$ (16)	$ (45)	$ 18	$ 9	$ 25	(50)	7	76
Derivative, Gain (Loss) on Derivatives, Total Net									(82)	512	(76)
Net gains (losses) on derivative contracts [Domain] | Credit Derivatives [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									2	(1)	16
Net gains (losses) on derivative contracts [Domain] | Interest Rate Swaps [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									(6)	1	49
Net gains (losses) on derivative contracts [Domain] | Futures Contracts [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									(45)	7	11
Income Loss On Variable Interest Entities [Member] | Variable Interest Entity [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									(32)	505	(152)
Income Loss On Variable Interest Entities [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									(20)	493	(127)
Income Loss On Variable Interest Entities [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									$ (12)	$ 11	$ (26)