Investment Securities - Schedule of Unrealized Loss on Investments (Details) - USD ($)	Sep. 30, 2025	Dec. 31, 2024
Less than 12 months
Fair value	$ 872,000,000	$ 947,000,000
Unrealized loss	(4,000,000)	(22,000,000)
12 months or longer
Fair value	16,542,000,000	21,069,000,000
Unrealized loss	(3,039,000,000)	(4,383,000,000)
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	604,000,000	1,873,000,000
Unrealized loss	(55,000,000)	(200,000,000)
U.S. States and political subdivisions
Less than 12 months
Fair value	53,000,000	87,000,000
Unrealized loss	(1,000,000)	(2,000,000)
12 months or longer
Fair value	426,000,000	472,000,000
Unrealized loss	(79,000,000)	(85,000,000)
Foreign government
Less than 12 months
Fair value	16,000,000	40,000,000
Unrealized loss	0	0
12 months or longer
Fair value	77,000,000	112,000,000
Unrealized loss	(3,000,000)	(5,000,000)
Agency mortgage-backed residential
Less than 12 months
Fair value	547,000,000	127,000,000
Unrealized loss	(1,000,000)	(3,000,000)
12 months or longer
Fair value	10,451,000,000	13,518,000,000
Unrealized loss	(2,154,000,000)	(3,109,000,000)
Mortgage-backed residential
Less than 12 months
Fair value	0	0
Unrealized loss	0	0
12 months or longer
Fair value	200,000,000	206,000,000
Unrealized loss	(35,000,000)	(43,000,000)
Agency mortgage-backed commercial
Less than 12 months
Fair value	191,000,000	428,000,000
Unrealized loss	(1,000,000)	(11,000,000)
12 months or longer
Fair value	3,590,000,000	3,445,000,000
Unrealized loss	(646,000,000)	(825,000,000)
Asset-backed
Less than 12 months
Fair value	0	0
Unrealized loss	0	0
12 months or longer
Fair value	24,000,000	124,000,000
Unrealized loss	0	(2,000,000)
Corporate debt
Less than 12 months
Fair value	65,000,000	265,000,000
Unrealized loss	(1,000,000)	(6,000,000)
12 months or longer
Fair value	1,170,000,000	1,319,000,000
Unrealized loss	$ (67,000,000)	$ (114,000,000)