Investment Securities - Gross Unrealized Losses (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Estimated fair value, less than 12 months	$ 699	$ 4,311
Gross unrealized losses, less than 12 months	(2)	(83)
Estimated fair value, 12 months or more	2,135	52
Gross unrealized losses, more than 12 months	(37)	(1)
State and municipal obligations
Debt Securities, Available-for-Sale [Line Items]
Estimated fair value, less than 12 months	20	52
Gross unrealized losses, less than 12 months	(1)	(10)
Estimated fair value, 12 months or more	30	0
Gross unrealized losses, more than 12 months	(9)	0
U.S. Government treasury obligations
Debt Securities, Available-for-Sale [Line Items]
Estimated fair value, less than 12 months	0	3,710
Gross unrealized losses, less than 12 months	0	(72)
Estimated fair value, 12 months or more	2,098	52
Gross unrealized losses, more than 12 months	(27)	(1)
Mortgage-backed securities
Debt Securities, Available-for-Sale [Line Items]
Estimated fair value, less than 12 months	0	0
Gross unrealized losses, less than 12 months	0	0
Estimated fair value, 12 months or more	7	0
Gross unrealized losses, more than 12 months	(1)	0
Foreign government bonds and obligations
Debt Securities, Available-for-Sale [Line Items]
Estimated fair value, less than 12 months	679	549
Gross unrealized losses, less than 12 months	(1)	(1)
Estimated fair value, 12 months or more	0	0
Gross unrealized losses, more than 12 months	$ 0	$ 0