Investment Securities - Summary (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Accrued interest available-for-sale debt securities	$ 12	$ 12	$ 12
Debt securities
Cost	3,133	3,133
Estimated Fair Value	3,094	3,094
Equity securities
Cost	60	60	50
Gross Unrealized Gains		20	0
Gross Unrealized Losses		(14)	(9)
Estimated Fair Value	66	66	41
Total Cost	3,193	3,193	4,671
Total Gross Unrealized Gains		20	0
Total Gross Unrealized Losses		(53)	(93)
Total Estimated Fair Value	3,160	3,160	4,578
Other assets	20,004	20,004	17,689
New public companies
Equity securities
Cost	10	10
Gross Unrealized Gains	37
Estimated Fair Value	26	26
State and municipal obligations
Debt securities
Cost	62	62	64
Gross Unrealized Gains		0	0
Gross Unrealized Losses		(10)	(10)
Estimated Fair Value	52	52	54
U.S. Government agency obligations
Debt securities
Cost	4	4	5
Gross Unrealized Gains		0	0
Gross Unrealized Losses		0	0
Estimated Fair Value	4	4	5
U.S. Government treasury obligations
Debt securities
Cost	2,214	2,214	3,859
Gross Unrealized Gains		0	0
Gross Unrealized Losses		(27)	(73)
Estimated Fair Value	2,187	2,187	3,786
Equity securities
Other assets	1,000	1,000
Non-cash transfer from investments	1,000
Mortgage-backed securities
Debt securities
Cost	12	12	13
Gross Unrealized Gains		0	0
Gross Unrealized Losses		(1)	0
Estimated Fair Value	11	11	13
Foreign government bonds and obligations
Debt securities
Cost	777	777	633
Gross Unrealized Gains		0	0
Gross Unrealized Losses		(1)	(1)
Estimated Fair Value	776	776	632
Other
Debt securities
Cost	64	64	47
Gross Unrealized Gains		0	0
Gross Unrealized Losses		0	0
Estimated Fair Value	$ 64	$ 64	$ 47