Loans and Leases - Balances Of Commercial Loan Portfolio Classes, Disaggregated By PD Grade (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 55,435	$ 58,232
Commercial and industrial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, originated year one	5,883	9,331
Financing receivable, originated year two	4,356	5,308
Financing receivable, originated year three	3,957	2,812
Financing receivable, originated year four	1,847	1,829
Financing receivable, originated year five	1,362	1,240
Financing receivable, originated prior to year five	2,652	2,267
LMC, Non-Revolving Loans	5,139	5,404
Revolving loans	6,255	4,793
Revolving Loans converted to term loans	65	120
Loans and leases	31,516	33,104
Revolving loans converted to term loan during period	0	50
Commercial and industrial | PD Grade 1 -12 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, originated year one	5,822	9,060
Financing receivable, originated year two	4,208	5,138
Financing receivable, originated year three	3,809	2,628
Financing receivable, originated year four	1,682	1,748
Financing receivable, originated year five	1,294	1,161
Financing receivable, originated prior to year five	2,551	2,145
LMC, Non-Revolving Loans	5,139	5,404
Revolving loans	5,972	4,571
Revolving Loans converted to term loans	13	60
Loans and leases	30,490	31,915
Commercial and industrial | PD Grade 13 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, originated year one	20	89
Financing receivable, originated year two	37	93
Financing receivable, originated year three	74	70
Financing receivable, originated year four	59	31
Financing receivable, originated year five	38	37
Financing receivable, originated prior to year five	48	64
LMC, Non-Revolving Loans	0	0
Revolving loans	154	127
Revolving Loans converted to term loans	4	1
Loans and leases	434	512
Commercial and industrial | PD Grade 14 15 16 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, originated year one	41	182
Financing receivable, originated year two	111	77
Financing receivable, originated year three	74	114
Financing receivable, originated year four	106	50
Financing receivable, originated year five	30	42
Financing receivable, originated prior to year five	53	58
LMC, Non-Revolving Loans	0	0
Revolving loans	129	95
Revolving Loans converted to term loans	48	59
Loans and leases	592	677
Commercial real estate | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,194	12,275
Commercial real estate | CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, originated year one	2,230	2,555
Financing receivable, originated year two	2,307	3,348
Financing receivable, originated year three	2,876	1,888
Financing receivable, originated year four	1,395	1,257
Financing receivable, originated year five	913	1,044
Financing receivable, originated prior to year five	2,189	1,887
Revolving loans	284	277
Revolving Loans converted to term loans	0	19
Loans and leases	12,194	12,275
Commercial real estate | PD Grade 1 -12 | CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, originated year one	2,216	2,477
Financing receivable, originated year two	2,264	3,311
Financing receivable, originated year three	2,814	1,750
Financing receivable, originated year four	1,208	1,140
Financing receivable, originated year five	806	946
Financing receivable, originated prior to year five	2,054	1,800
Revolving loans	259	259
Revolving Loans converted to term loans	0	19
Loans and leases	11,621	11,702
Commercial real estate | PD Grade 13 | CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, originated year one	4	48
Financing receivable, originated year two	26	24
Financing receivable, originated year three	50	117
Financing receivable, originated year four	171	75
Financing receivable, originated year five	69	71
Financing receivable, originated prior to year five	91	54
Revolving loans	0	0
Revolving Loans converted to term loans	0	0
Loans and leases	411	389
Commercial real estate | PD Grade 14 15 16 | CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, originated year one	10	30
Financing receivable, originated year two	17	13
Financing receivable, originated year three	12	21
Financing receivable, originated year four	16	42
Financing receivable, originated year five	38	27
Financing receivable, originated prior to year five	44	33
Revolving loans	25	18
Revolving Loans converted to term loans	0	0
Loans and leases	$ 162	$ 184