Investment Securities - Schedule of Unrealized Loss on Investments (Details) - USD ($)	Jun. 30, 2024	Dec. 31, 2023
Less than 12 months
Fair value	$ 399,000,000	$ 590,000,000
Unrealized loss	(6,000,000)	(10,000,000)
12 months or longer
Fair value	22,426,000,000	23,331,000,000
Unrealized loss	(4,503,000,000)	(4,000,000,000)
Credit reserves, available-for-sale	0	0
Credit reserves, held-to-maturity	0	0
U.S. Treasury and federal agencies
Less than 12 months
Fair value	0	0
Unrealized loss	0	0
12 months or longer
Fair value	2,047,000,000	2,075,000,000
Unrealized loss	(227,000,000)	(209,000,000)
U.S. States and political subdivisions
Less than 12 months
Fair value	65,000,000	70,000,000
Unrealized loss	(1,000,000)	0
12 months or longer
Fair value	524,000,000	501,000,000
Unrealized loss	(81,000,000)	(70,000,000)
Foreign government
Less than 12 months
Fair value	16,000,000	16,000,000
Unrealized loss	0	0
12 months or longer
Fair value	134,000,000	134,000,000
Unrealized loss	(9,000,000)	(8,000,000)
Agency mortgage-backed residential
Less than 12 months
Fair value	92,000,000	300,000,000
Unrealized loss	(1,000,000)	(5,000,000)
12 months or longer
Fair value	14,231,000,000	15,015,000,000
Unrealized loss	(3,154,000,000)	(2,734,000,000)
Mortgage-backed residential
Less than 12 months
Fair value	0	0
Unrealized loss	0	0
12 months or longer
Fair value	214,000,000	225,000,000
Unrealized loss	(45,000,000)	(43,000,000)
Agency mortgage-backed commercial
Less than 12 months
Fair value	138,000,000	153,000,000
Unrealized loss	(2,000,000)	(4,000,000)
12 months or longer
Fair value	3,523,000,000	3,472,000,000
Unrealized loss	(837,000,000)	(779,000,000)
Asset-backed
Less than 12 months
Fair value	0	18,000,000
Unrealized loss	0	0
12 months or longer
Fair value	252,000,000	302,000,000
Unrealized loss	(6,000,000)	(12,000,000)
Corporate debt
Less than 12 months
Fair value	88,000,000	33,000,000
Unrealized loss	(2,000,000)	(1,000,000)
12 months or longer
Fair value	1,501,000,000	1,607,000,000
Unrealized loss	$ (144,000,000)	$ (145,000,000)