Investment Securities - Summary (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale [Line Items]
Accrued interest available-for-sale debt securities	$ 3	$ 5
Debt securities
Cost	1,181
Estimated Fair Value	1,169	2,120
Equity securities
Cost	50	60
Gross Unrealized Gains	0	16
Gross Unrealized Losses	(9)	(10)
Estimated Fair Value	41	66
Total Cost	1,231	2,198
Total Gross Unrealized Gains	0	17
Total Gross Unrealized Losses	(21)	(29)
Total Estimated Fair Value	1,210	2,186
State and municipal obligations
Debt securities
Cost	60	61
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7)	(6)
Estimated Fair Value	53	55
U.S. Government agency obligations
Debt securities
Cost	4	4
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	4	4
U.S. Government treasury obligations
Debt securities
Cost	270	1,217
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(4)	(12)
Estimated Fair Value	266	1,206
Mortgage-backed securities
Debt securities
Cost	11	12
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	10	11
Foreign government bonds and obligations
Debt securities
Cost	762	770
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	762	770
Other
Debt securities
Cost	74	74
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 74	$ 74