Allowance for Credit Losses - Rollforward of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 814	$ 821	$ 815	$ 773
Charge-offs	(35)	(33)	(119)	(128)
Recoveries	9	9	30	30
Provision for loan and lease losses	(11)	26	51	148
Ending balance	777	823	777	823
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	87	66	79	83
Provision for remaining unfunded commitments	6	9	14	(8)
Ending balance	93	75	93	75
Allowance for credit losses	870	898	870	898
Commercial: | Commercial, financial, and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	347	344	345	339
Charge-offs	(25)	(12)	(86)	(64)
Recoveries	6	4	19	19
Provision for loan and lease losses	6	16	56	58
Ending balance	334	352	334	352
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	68	44	57	49
Provision for remaining unfunded commitments	6	11	17	6
Ending balance	74	55	74	55
Allowance for credit losses	408	407	408	407
Commercial: | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	213	221	227	172
Charge-offs	(3)	(15)	(14)	(47)
Recoveries	0	1	3	1
Provision for loan and lease losses	(6)	11	(12)	92
Ending balance	204	218	204	218
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	10	10	11	22
Provision for remaining unfunded commitments	0	(2)	(1)	(14)
Ending balance	10	8	10	8
Allowance for credit losses	214	226	214	226
Consumer: | Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	233	231	221	233
Charge-offs	(1)	(1)	(3)	(2)
Recoveries	2	3	4	6
Provision for loan and lease losses	(15)	(3)	(3)	(7)
Ending balance	219	230	219	230
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	9	12	11	12
Provision for remaining unfunded commitments	0	0	(2)	0
Ending balance	9	12	9	12
Allowance for credit losses	228	242	228	242
Consumer: | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	21	25	22	29
Charge-offs	(6)	(5)	(16)	(15)
Recoveries	1	1	4	4
Provision for loan and lease losses	4	2	10	5
Ending balance	20	23	20	23
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	0	0	0	0
Provision for remaining unfunded commitments	0	0	0	0
Ending balance	0	0	0	0
Allowance for credit losses	$ 20	$ 23	$ 20	$ 23