Derivative Instruments - Summary of Effective Portion of Gains (Losses) Recognized in Other Comprehensive Income (Loss) and Gains (Losses) Reclassified from Other Comprehensive Income (Loss) into Earnings (Detail) - Asset and Liability Management Positions [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Cash Flow Hedges [Member] | Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Losses) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ 6	$ 21	$ 91	$ (171)
Derivative Instruments, Gains (Losses) Reclassified from Other Comprehensive Income (Loss) into Earnings	(6)	(2)	(3)	(5)
Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Losses) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	17	(4)	16	6
Net Investment Hedges [Member] | Non Derivative Debt Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Losses) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ 27	$ (45)	$ 61	$ (41)