Investment Securities - Gross Unrealized Losses Ratio to Fair Value (Details) $ in Millions	Sep. 30, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Debt Securities, Available-for-Sale [Line Items]
Number of securities, less than 12 months | security	53	88
Estimated fair value, less than 12 months	$ 699	$ 4,311
Gross unrealized losses, less than 12 months	$ (2)	$ (83)
Number of securities, 12 months or more | security	76	3
Estimated fair value, 12 months or more	$ 2,135	$ 52
Gross unrealized losses, more than 12 months	$ (37)	$ (1)
Number of securities, total | security	129	91
Estimated fair value, total	$ 2,834	$ 4,363
Gross unrealized losses, total	$ (39)	$ (84)
90–100%
Debt Securities, Available-for-Sale [Line Items]
Number of securities, less than 12 months | security	53	74
Estimated fair value, less than 12 months	$ 699	$ 4,287
Gross unrealized losses, less than 12 months	$ (2)	$ (74)
Number of securities, 12 months or more | security	44	3
Estimated fair value, 12 months or more	$ 2,107	$ 52
Gross unrealized losses, more than 12 months	$ (27)	$ (1)
Number of securities, total | security	97	77
Estimated fair value, total	$ 2,806	$ 4,339
Gross unrealized losses, total	$ (29)	$ (75)
Less than 90%
Debt Securities, Available-for-Sale [Line Items]
Number of securities, less than 12 months | security	0	14
Estimated fair value, less than 12 months	$ 0	$ 24
Gross unrealized losses, less than 12 months	$ 0	$ (9)
Number of securities, 12 months or more | security	32	0
Estimated fair value, 12 months or more	$ 28	$ 0
Gross unrealized losses, more than 12 months	$ (10)	$ 0
Number of securities, total | security	32	14
Estimated fair value, total	$ 28	$ 24
Gross unrealized losses, total	$ (10)	$ (9)