Securities- Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Securities held to maturity:
Amortized Cost	$ 2,541	$ 2,593
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(200)	(184)
Fair Value	2,341	2,410
Allowance for credit losses- securities held to maturity	(2)	(2)
Securities HTM, net of allowance for credit losses	2,539	2,591
Securities available for sale:
Amortized Cost	17,203	6,699
Gross Unrealized Gains	15	31
Gross Unrealized Losses	(279)	(163)
Fair Value	16,939	6,567
Accrued interest receivable on investment securities held to maturity	16	26
Discount (premium) included in amortized cost of investment securities HTM	(14)	(16)
Accrued interest receivable on investment securities available for sale	133	111
U.S. Treasury securities
Securities held to maturity:
Amortized Cost	20	20
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	19	20
Securities available for sale:
Amortized Cost	2,739	1,576
Gross Unrealized Gains	0	10
Gross Unrealized Losses	(16)	0
Fair Value	2,723	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	208	210
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(16)	(15)
Fair Value	192	195
Mortgage-backed securities
Securities held to maturity:
Amortized Cost	338	350
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(17)	(18)
Fair Value	321	332
Securities available for sale:
Amortized Cost	12,481	2,852
Gross Unrealized Gains	10	11
Gross Unrealized Losses	(153)	(69)
Fair Value	12,338	2,794
State and municipal securities
Securities held to maturity:
Amortized Cost	1,782	1,821
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(171)	(155)
Fair Value	1,611	1,667
Securities available for sale:
Amortized Cost	1,486	1,768
Gross Unrealized Gains	4	8
Gross Unrealized Losses	(83)	(67)
Fair Value	1,407	1,709
Asset-backed securities
Securities held to maturity:
Amortized Cost	107	108
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	(2)
Fair Value	105	106
Corporate notes and other
Securities held to maturity:
Amortized Cost	68	68
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4)	(4)
Fair Value	64	64
Securities available for sale:
Amortized Cost	289	293
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(11)	(12)
Fair Value	$ 279	$ 283

Debt Securities, Held-To-Maturity, Discount (Premium)

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