Loans and Leases - Balances Of Commercial Loan Portfolio Classes, Disaggregated By PD Grade (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 58,232	$ 31,061
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	33,104
Commercial and industrial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	9,331
2019	5,308
2018	2,812
2017	1,829
2016	1,240
Prior to 2016	2,267
Non-revolving loans	5,404
Revolving Loans	4,793
Revolving loans converted to term loans	120
Finance receivable converted from revolving to term loan	50
Commercial and industrial | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	5,400
Commercial and industrial | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	210	$ 218
Commercial and industrial | Pass (PD grades 1 through 12) | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	9,081
2019	5,145
2018	2,640
2017	1,762
2016	1,161
Prior to 2016	2,163
Non-revolving loans	5,404
Revolving Loans	4,575
Revolving loans converted to term loans	62
Loans, net of unearned income	31,993
Commercial and industrial | PD Grades 13 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	89
2019	93
2018	70
2017	31
2016	37
Prior to 2016	64
Non-revolving loans	0
Revolving Loans	127
Revolving loans converted to term loans	1
Loans, net of unearned income	512
Commercial and industrial | PD Grades 14 15 16 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	161
2019	70
2018	102
2017	36
2016	42
Prior to 2016	40
Non-revolving loans	0
Revolving Loans	91
Revolving loans converted to term loans	57
Loans, net of unearned income	599
Commercial real estate | CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	2,555
2019	3,348
2018	1,888
2017	1,257
2016	1,044
Prior to 2016	1,887
Revolving Loans	277
Revolving loans converted to term loans	19
Loans, net of unearned income	12,275
Commercial real estate | Pass (PD grades 1 through 12) | CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	2,501
2019	3,311
2018	1,750
2017	1,140
2016	946
Prior to 2016	1,800
Revolving Loans	277
Revolving loans converted to term loans	19
Loans, net of unearned income	11,744
Commercial real estate | PD Grades 13 | CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	48
2019	24
2018	117
2017	75
2016	71
Prior to 2016	54
Revolving Loans	0
Revolving loans converted to term loans	0
Loans, net of unearned income	389
Commercial real estate | PD Grades 14 15 16 | CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	6
2019	13
2018	21
2017	42
2016	27
Prior to 2016	33
Revolving Loans	0
Revolving loans converted to term loans	0
Loans, net of unearned income	$ 142