Allowance for Credit Losses - Rollforward of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 737	$ 624	$ 685	$ 670	$ 670
Charge-offs	(104)	(21)	(159)	(61)
Recoveries	9	9	25	27
Ending balance	760	664	760	664	$ 685
Accounting Standards Update [Extensible List]					Accounting Standards Update 2022-02
Loans and leases	61,778		61,778		$ 58,102
Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			(6)
Ending balance					(6)
Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	842	752	842	752
Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	118	52	215	28
Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	90	80	87	66	66
Provision for loan and lease losses	(8)	8	(5)	22
Ending balance	82	88	82	88	87
Commercial: | Commercial, financial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	326	274	308	334	334
Charge-offs	(91)	(13)	(124)	(38)
Recoveries	5	2	12	6
Ending balance	335	295	335	295	308
Loans and leases	33,163		33,163		31,781
Commercial: | Commercial, financial and industrial | Single Company
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs			(72)
Commercial: | Commercial, financial and industrial | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			1
Ending balance					1
Commercial: | Commercial, financial and industrial | Paycheck Protection Plan
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	35	129	35	129	76
Commercial: | Commercial, financial and industrial | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	384	353	384	353
Commercial: | Commercial, financial and industrial | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	95	32	138	(7)
Commercial: | Commercial, financial and industrial | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	55	53	55	46	46
Provision for loan and lease losses	(6)	5	(6)	12
Ending balance	49	58	49	58	55
Commercial: | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	159	141	146	154	154
Charge-offs	(5)	(1)	(15)	(1)
Recoveries	1	0	2	1
Ending balance	169	148	169	148	146
Loans and leases	14,121		14,121		13,228
Commercial: | Commercial Real Estate | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			0
Ending balance					0
Commercial: | Commercial Real Estate | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	190	167	190	167
Commercial: | Commercial Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	14	8	36	(6)
Commercial: | Commercial Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	24	17	22	12	12
Provision for loan and lease losses	(3)	2	(1)	7
Ending balance	21	19	21	19	22
Commercial: | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	187		187		193
Consumer:
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	13,685		13,685		12,253
Consumer: | Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	221	183	200	163	163
Charge-offs	(1)	(1)	(3)	(4)
Recoveries	2	6	7	17
Ending balance	228	193	228	193	200
Loans and leases	13,685		13,685		12,253
Consumer: | Consumer Real Estate | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			(7)
Ending balance					(7)
Consumer: | Consumer Real Estate | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	240	204	240	204
Consumer: | Consumer Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	6	5	31	17
Consumer: | Consumer Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	11	10	10	8	8
Provision for loan and lease losses	1	1	2	3
Ending balance	12	11	12	11	10
Consumer: | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	31	26	31	19	19
Charge-offs	(7)	(6)	(17)	(18)
Recoveries	1	1	4	3
Ending balance	28	28	28	28	31
Loans and leases	809		809		840
Consumer: | Credit Card and Other | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			0
Ending balance					0
Consumer: | Credit Card and Other | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	28	28	28	28
Consumer: | Credit Card and Other | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	3	7	10	24
Consumer: | Credit Card and Other | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0	0	0
Provision for loan and lease losses	0	0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0	$ 0