Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on related derivatives	$ 373	$ 214	$ 641	$ 243
Gain (loss) on instruments designated at fair value and related derivatives	(3)	(3)	(7)	(33)
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	(378)	(259)	(663)	(350)
Credit risk component, total	(8)	1	(16)	0
Total mark-to-market on financial instruments designated at fair value	(386)	(258)	(679)	(350)
Mark-to-market on related derivatives	382	256	669	319
Net realized gain (loss) on related long-term debt derivatives	1	(1)	3	(2)
Gain (loss) on instruments designated at fair value and related derivatives	(3)	(3)	(7)	(33)
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	0
Credit risk component, assets	(8)	1	(16)	0
Total mark-to-market on financial instruments designated at fair value	(8)	1	(16)	0
Mark-to-market on related derivatives	0	0	0	0
Net realized gain (loss) on related long-term debt derivatives	0	0	0	0
Gain (loss) on instruments designated at fair value and related derivatives	(8)	1	(16)	0
Gain (loss) on instruments designated at fair value and related derivatives | Long-term debt
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	(1)	(33)	(22)	(3)
Credit risk component, liabilities	0	0	0	0
Total mark-to-market on financial instruments designated at fair value	(1)	(33)	(22)	(3)
Mark-to-market on related derivatives	1	38	24	3
Net realized gain (loss) on related long-term debt derivatives	1	(1)	3	(2)
Gain (loss) on instruments designated at fair value and related derivatives	1	4	5	(2)
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	(377)	(226)	(641)	(347)
Credit risk component, liabilities	0	0	0	0
Total mark-to-market on financial instruments designated at fair value	(377)	(226)	(641)	(347)
Mark-to-market on related derivatives	381	218	645	316
Net realized gain (loss) on related long-term debt derivatives	0	0	0	0
Gain (loss) on instruments designated at fair value and related derivatives	$ 4	$ (8)	$ 4	$ (31)