Fair Value Measurements - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Unfunded commitments, equity securities measured at net asset value	$ 20		$ 20			$ 21
Revaluation period			90 days
Deferred fee income	3		$ 3			3
Unfunded Loan Commitment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fee income	167		167			162
Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Transfers Out of Level 3	219	$ 198	465	$ 832
Assets Transfers out of Level 3	(24)	(2)	(42)	(19)
Transfers into Level 3	3	48	51	84
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	46	40	50	39
Fair Value (in millions)	216	16	216	16	$ 185	138	$ 77	$ (83)
Level 3 | Equity contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivatives, net, Transfers out of Level 3	12	(3)	29	2
Level 3 | Long-term debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Transfers Out of Level 3	166	197	398	800
Transfers into Level 3	3	48	50	84
Level 3 | Deposits
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Transfers Out of Level 3	53	1	67	32
Transfers into Level 3	0	0	1	0
Level 3 | Commercial loans held for sale | Loans, net
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets Transfers out of Level 3	(15)	(5)	(19)	(17)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	43	36	55	36
Fair Value (in millions)	$ 78	$ 36	$ 78	$ 36	$ 44	$ 32	$ 3	$ 49