Securities- Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Securities held to maturity:
Amortized Cost	$ 2,381	$ 2,593
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(331)	(184)
Fair Value	2,050	2,410
Allowance for credit losses- securities held to maturity	(1)	(2)
Securities HTM, net of allowance for credit losses	2,380	2,591
Securities available for sale:
Amortized Cost	19,128	6,699
Gross Unrealized Gains	11	31
Gross Unrealized Losses	(949)	(163)
Fair Value	18,190	6,567
Accrued interest receivable on investment securities held to maturity	16	26
Debt security, premium	10	16
Accrued interest receivable on investment securities available for sale	87	42
U.S. Treasury securities
Securities held to maturity:
Amortized Cost		20
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		20
Securities available for sale:
Amortized Cost	2,801	1,576
Gross Unrealized Gains	11	10
Gross Unrealized Losses	(51)	0
Fair Value	2,761	1,586
U.S. Government agency securities
Securities held to maturity:
Amortized Cost	226	226
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5)	(5)
Fair Value	221	221
Securities available for sale:
Amortized Cost	204	210
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(21)	(15)
Fair Value	183	195
Mortgage-backed securities
Securities held to maturity:
Amortized Cost	319	350
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(26)	(18)
Fair Value	293	332
Securities available for sale:
Amortized Cost	15,335	2,852
Gross Unrealized Gains	0	11
Gross Unrealized Losses	(801)	(69)
Fair Value	14,534	2,794
State and municipal securities
Securities held to maturity:
Amortized Cost	1,716	1,821
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(294)	(155)
Fair Value	1,422	1,667
Securities available for sale:
Amortized Cost	505	1,768
Gross Unrealized Gains	0	8
Gross Unrealized Losses	(61)	(67)
Fair Value	444	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	65	68
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4)	(4)
Fair Value	61	64
Securities available for sale:
Amortized Cost	283	293
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(15)	(12)
Fair Value	$ 268	$ 283

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