Investment Securities - Gross Unrealized Losses Ratio to Fair Value (Details) $ in Millions	Jun. 30, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Number of Securities
Less than 12 months | security	0	0
12 months or more | security	63	71
Total | security	63	71
Estimated Fair Value
Less than 12 months	$ 0	$ 0
12 months or more	188	1,154
Total	188	1,154
Gross Unrealized Losses
Less than 12 months	0	0
12 months or more	(12)	(19)
Total	$ (12)	$ (19)
90–100%
Number of Securities
Less than 12 months | security	0	0
12 months or more | security	52	69
Total | security	52	69
Estimated Fair Value
Less than 12 months	$ 0	$ 0
12 months or more	172	1,140
Total	172	1,140
Gross Unrealized Losses
Less than 12 months	0	0
12 months or more	(6)	(14)
Total	$ (6)	$ (14)
Less than 90%
Number of Securities
Less than 12 months | security	0	0
12 months or more | security	11	2
Total | security	11	2
Estimated Fair Value
Less than 12 months	$ 0	$ 0
12 months or more	16	14
Total	16	14
Gross Unrealized Losses
Less than 12 months	0	0
12 months or more	(6)	(5)
Total	$ (6)	$ (5)