Investment Securities - Gross Unrealized Losses Ratio to Fair Value (Details) $ in Millions	Mar. 31, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Number of Securities
Less than 12 months | security	0	0
12 months or more | security	76	71
Total | security	76	71
Estimated Fair Value
Less than 12 months	$ 0	$ 0
12 months or more	1,134	1,154
Total	1,134	1,154
Gross Unrealized Losses
Less than 12 months	0	0
12 months or more	(16)	(19)
Total	$ (16)	$ (19)
90–100%
Number of Securities
Less than 12 months | security	0	0
12 months or more | security	68	69
Total | security	68	69
Estimated Fair Value
Less than 12 months	$ 0	$ 0
12 months or more	1,119	1,140
Total	1,119	1,140
Gross Unrealized Losses
Less than 12 months	0	0
12 months or more	(10)	(14)
Total	$ (10)	$ (14)
Less than 90%
Number of Securities
Less than 12 months | security	0	0
12 months or more | security	8	2
Total | security	8	2
Estimated Fair Value
Less than 12 months	$ 0	$ 0
12 months or more	15	14
Total	15	14
Gross Unrealized Losses
Less than 12 months	0	0
12 months or more	(6)	(5)
Total	$ (6)	$ (5)