Asset Quality - Aging Analysis of Past Due and Current Loans (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Total	$ 106,600	$ 101,854
Accrued interest	193	198
Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	73,920	70,836
Accrued interest	117	113
Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	32,680	31,018
Accrued interest	75	85
Commercial and Industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	52,815	50,525
Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	15,124	14,244
Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	2,065	1,996
Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	17,189	16,240
Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	3,916	4,071
Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	17,181	15,756
Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	8,258	8,467
Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	6,249	5,753
Commercial credit card | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	147	139
Commercial credit card | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	930	972
Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	62	70
Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total	105,984	101,167
Financial Asset, Not Past Due | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	73,581	70,439
Financial Asset, Not Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	32,403	30,728
Financial Asset, Not Past Due | Commercial and Industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	52,537	50,226
Financial Asset, Not Past Due | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	15,072	14,174
Financial Asset, Not Past Due | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	2,064	1,978
Financial Asset, Not Past Due | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	17,136	16,152
Financial Asset, Not Past Due | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	3,908	4,061
Financial Asset, Not Past Due | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	17,098	15,669
Financial Asset, Not Past Due | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	8,102	8,299
Financial Asset, Not Past Due | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	6,229	5,736
Financial Asset, Not Past Due | Commercial credit card | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	914	956
Financial Asset, Not Past Due | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	60	68
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	70	76
30-59 Days Past Due | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	32	35
30-59 Days Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	38	41
30-59 Days Past Due | Commercial and Industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	23	19
30-59 Days Past Due | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	4	10
30-59 Days Past Due | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	1	0
30-59 Days Past Due | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	5	10
30-59 Days Past Due | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	4	6
30-59 Days Past Due | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	7	7
30-59 Days Past Due | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	18	21
30-59 Days Past Due | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	8	8
30-59 Days Past Due | Commercial credit card | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	4	4
30-59 Days Past Due | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	1	1
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	52	89
60-89 Days Past Due | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	37	75
60-89 Days Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	15	14
60-89 Days Past Due | Commercial and Industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	31	49
60-89 Days Past Due | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	5	9
60-89 Days Past Due | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	0	17
60-89 Days Past Due | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	5	26
60-89 Days Past Due | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	1	0
60-89 Days Past Due | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	2	3
60-89 Days Past Due | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	6	6
60-89 Days Past Due | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	4	2
60-89 Days Past Due | Commercial credit card | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	3	3
60-89 Days Past Due | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	0	0
90 and Greater Days Past Due
Financing Receivable, Past Due [Line Items]
Total	55	68
90 and Greater Days Past Due | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	41	48
90 and Greater Days Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	14	20
90 and Greater Days Past Due | Commercial and Industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	38	40
90 and Greater Days Past Due | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	3	7
90 and Greater Days Past Due | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	0	1
90 and Greater Days Past Due | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	3	8
90 and Greater Days Past Due | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	0	0
90 and Greater Days Past Due | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	1	5
90 and Greater Days Past Due | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	3	6
90 and Greater Days Past Due | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	4	3
90 and Greater Days Past Due | Commercial credit card | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	6	6
90 and Greater Days Past Due | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	0	0
Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total	616	687
Financial Asset, Past Due | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	339	397
Financial Asset, Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	277	290
Financial Asset, Past Due | Commercial and Industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	278	299
Financial Asset, Past Due | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	52	70
Financial Asset, Past Due | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	1	18
Financial Asset, Past Due | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	53	88
Financial Asset, Past Due | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	8	10
Financial Asset, Past Due | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	83	87
Financial Asset, Past Due | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	156	168
Financial Asset, Past Due | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	20	17
Financial Asset, Past Due | Commercial credit card | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	16	16
Financial Asset, Past Due | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	2	2
Nonperforming financial instruments
Financing Receivable, Past Due [Line Items]
Total	439	454
Nonperforming financial instruments | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	229	239
Nonperforming financial instruments | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	210	215
Nonperforming financial instruments | Commercial and Industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	186	191
Nonperforming financial instruments | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	40	44
Nonperforming financial instruments | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	0	0
Nonperforming financial instruments | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	40	44
Nonperforming financial instruments | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	3	4
Nonperforming financial instruments | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	73	72
Nonperforming financial instruments | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	129	135
Nonperforming financial instruments | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	4	4
Nonperforming financial instruments | Commercial credit card | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	3	3
Nonperforming financial instruments | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	$ 1	$ 1