Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on related derivatives	$ 1,055	$ 824	$ 2,082
Gain (loss) on instruments designated at fair value and related derivatives	35	34	(13)
Gain (loss) on instruments designated at fair value and related derivatives
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	(1,045)	(774)	(2,186)
Credit risk component, total	2	(49)	3
Total mark-to-market on financial instruments designated at fair value	(1,043)	(823)	(2,183)
Mark-to-market on related derivatives	1,040	824	2,131
Net realized gain on related long-term debt derivatives	38	33	39
Gain (loss) on instruments designated at fair value and related derivatives	35	34	(13)
Gain (loss) on instruments designated at fair value and related derivatives | Loans
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	0	0	0
Credit risk component, assets	2	(49)	3
Total mark-to-market on financial instruments designated at fair value	2	(49)	3
Mark-to-market on related derivatives	0	37	0
Net realized gain on related long-term debt derivatives	0	0	0
Gain (loss) on instruments designated at fair value and related derivatives	2	(12)	3
Gain (loss) on instruments designated at fair value and related derivatives | Fixed rate long-term debt
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	74	(79)	(200)
Credit risk component, liabilities	0	0	0
Total mark-to-market on financial instruments designated at fair value	74	(79)	(200)
Mark-to-market on related derivatives	(88)	88	148
Net realized gain on related long-term debt derivatives	38	33	39
Gain (loss) on instruments designated at fair value and related derivatives	24	42	(13)
Gain (loss) on instruments designated at fair value and related derivatives | Hybrid Instruments
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	(1,119)	(695)	(1,986)
Credit risk component, liabilities	0	0	0
Total mark-to-market on financial instruments designated at fair value	(1,119)	(695)	(1,986)
Mark-to-market on related derivatives	1,128	699	1,983
Net realized gain on related long-term debt derivatives	0	0	0
Gain (loss) on instruments designated at fair value and related derivatives	$ 9	$ 4	$ (3)