Allowance for Credit Losses - Rollforward of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 822	$ 787	$ 815	$ 773
Charge-offs	(43)	(49)	(84)	(95)
Recoveries	9	15	21	21
Provision for loan and lease losses	26	68	62	122
Ending balance	814	821	814	821
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	83	79	79	83
Provision for remaining unfunded commitments	4	(13)	8	(17)
Ending balance	87	66	87	66
Allowance for credit losses	901	887	901	887
Commercial: | Commercial, financial, and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	345	348	345	339
Charge-offs	(28)	(24)	(62)	(52)
Recoveries	6	12	12	14
Provision for loan and lease losses	24	8	52	43
Ending balance	347	344	347	344
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	63	49	57	49
Provision for remaining unfunded commitments	5	(5)	11	(5)
Ending balance	68	44	68	44
Allowance for credit losses	415	388	415	388
Commercial: | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	225	181	227	172
Charge-offs	(7)	(19)	(10)	(32)
Recoveries	0	0	3	0
Provision for loan and lease losses	(5)	59	(7)	81
Ending balance	213	221	213	221
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	9	18	11	22
Provision for remaining unfunded commitments	1	(8)	(1)	(12)
Ending balance	10	10	10	10
Allowance for credit losses	223	231	223	231
Consumer: | Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	230	231	221	233
Charge-offs	(2)	(1)	(2)	(1)
Recoveries	1	2	3	4
Provision for loan and lease losses	4	(1)	11	(5)
Ending balance	233	231	233	231
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	11	12	11	12
Provision for remaining unfunded commitments	(2)	0	(2)	0
Ending balance	9	12	9	12
Allowance for credit losses	242	243	242	243
Consumer: | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	22	27	22	29
Charge-offs	(6)	(5)	(10)	(10)
Recoveries	2	1	3	3
Provision for loan and lease losses	3	2	6	3
Ending balance	21	25	21	25
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	$ 21	$ 25	$ 21	$ 25