Investment Securities - Contractual Maturities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Total Estimated Fair Value
Due within 1 year	$ 1,778
Due after 1 year but within 5 years	261
Due after 5 years but within 10 years	32
Due after 10 years	49
Total	2,120	$ 4,537
Total Cost
Due within 1 year	1,784
Due after 1 year but within 5 years	265
Due after 5 years but within 10 years	33
Due after 10 years	56
Total	$ 2,138
Weighted average yields
Weighted average yields, due within 1 year	4.68%
Weighted average yields, due after 1 years but within 5 years	3.17%
Weighted average yields, due after 5 years but within 10 years	4.76%
Weighted average yield, due after 10 years	2.80%
Total	4.44%
U.S. statutory federal income tax rate	21.00%	21.00%	21.00%
State and municipal obligations
Total Estimated Fair Value
Due within 1 year	$ 0
Due after 1 year but within 5 years	1
Due after 5 years but within 10 years	20
Due after 10 years	34
Total	55	$ 54
Total Cost
Total	61	64
U.S. Government agency obligations
Total Estimated Fair Value
Due within 1 year	0
Due after 1 year but within 5 years	0
Due after 5 years but within 10 years	0
Due after 10 years	4
Total	4	5
Total Cost
Total	4	5
U.S. Government treasury obligations
Total Estimated Fair Value
Due within 1 year	1,010
Due after 1 year but within 5 years	194
Due after 5 years but within 10 years	2
Due after 10 years	0
Total	1,206	3,786
Total Cost
Total	1,217	3,859
Mortgage-backed securities
Total Estimated Fair Value
Due within 1 year	0
Due after 1 year but within 5 years	0
Due after 5 years but within 10 years	0
Due after 10 years	11
Total	11	13
Total Cost
Total	12	13
Foreign government bonds and obligations
Total Estimated Fair Value
Due within 1 year	768
Due after 1 year but within 5 years	2
Due after 5 years but within 10 years	0
Due after 10 years	0
Total	770	632
Total Cost
Total	770	633
Other
Total Estimated Fair Value
Due within 1 year	0
Due after 1 year but within 5 years	64
Due after 5 years but within 10 years	10
Due after 10 years	0
Total	74	47
Total Cost
Total	$ 74	$ 47