Securities- Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Securities held to maturity:
Amortized Cost	$ 2,450	$ 2,593
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(159)	(184)
Fair Value	2,292	2,410
Allowance for credit losses- securities held to maturity	(2)	(2)
Securities HTM, net of allowance for credit losses	2,448	2,591
Securities available for sale:
Amortized Cost	18,420	6,699
Gross Unrealized Gains	14	31
Gross Unrealized Losses	(281)	(163)
Fair Value	18,153	6,567
Accrued interest receivable on investment securities held to maturity	25	26
Debt security, premium	12	16
Accrued interest receivable on investment securities available for sale	78	42
U.S. Treasury securities
Securities held to maturity:
Amortized Cost	20	20
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	20	20
Securities available for sale:
Amortized Cost	2,860	1,576
Gross Unrealized Gains	0	10
Gross Unrealized Losses	(22)	0
Fair Value	2,838	1,586
U.S. Government agency securities
Securities held to maturity:
Amortized Cost	226	226
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4)	(5)
Fair Value	222	221
Securities available for sale:
Amortized Cost	205	210
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(17)	(15)
Fair Value	188	195
Mortgage-backed securities
Securities held to maturity:
Amortized Cost	334	350
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(19)	(18)
Fair Value	315	332
Securities available for sale:
Amortized Cost	14,550	2,852
Gross Unrealized Gains	10	11
Gross Unrealized Losses	(205)	(69)
Fair Value	14,355	2,794
State and municipal securities
Securities held to maturity:
Amortized Cost	1,748	1,821
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(130)	(155)
Fair Value	1,619	1,667
Securities available for sale:
Amortized Cost	519	1,768
Gross Unrealized Gains	3	8
Gross Unrealized Losses	(26)	(67)
Fair Value	496	1,709
Asset-backed securities
Securities held to maturity:
Amortized Cost	55	108
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	(2)
Fair Value	53	106
Corporate notes and other
Securities held to maturity:
Amortized Cost	67	68
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4)	(4)
Fair Value	63	64
Securities available for sale:
Amortized Cost	286	293
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(11)	(12)
Fair Value	$ 276	$ 283

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