Loans and Allowance for Loan Losses - Schedule of Rollforward of Allowance for Loan Losses (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Allowance for loan losses:
Beginning balance	$ 956	$ 422	$ 442	$ 414	$ 414
Purchased credit deteriorated loans			237
Purchased seasoned loans			241
Charge-offs	(70)	(22)	(185)	(62)	(96)
Recoveries	20	5	38	13
Provision for (reversal of) loan losses	80	29	213	69
Ending balance	986	434	986	434	442
Commercial & Industrial
Allowance for loan losses:
Beginning balance	500	233	255	221	221
Purchased credit deteriorated loans			110
Purchased seasoned loans			106
Charge-offs	(51)	(19)	(139)	(53)
Recoveries	15	4	25	9
Provision for (reversal of) loan losses	42	26	149	67
Ending balance	506	244	506	244	255
Commercial Real Estate
Allowance for loan losses:
Beginning balance	216	101	95	111	111
Purchased credit deteriorated loans			102
Purchased seasoned loans			67
Charge-offs	(8)	0	(9)	0
Recoveries	1	0	1	0
Provision for (reversal of) loan losses	13	(1)	(34)	(11)
Ending balance	222	100	222	100	95
Consumer
Allowance for loan losses:
Beginning balance	240	88	92	82	82
Purchased credit deteriorated loans			25
Purchased seasoned loans			68
Charge-offs	(11)	(3)	(37)	(9)
Recoveries	4	1	12	4
Provision for (reversal of) loan losses	25	4	98	13
Ending balance	$ 258	$ 90	$ 258	$ 90	$ 92

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

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Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

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