Asset Quality - Breakdown of Nonperforming TDRs by Loans Category (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022 USD ($) loan	Dec. 31, 2021 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	4,385	4,429
Pre-modification Outstanding Recorded Investment	$ 303	$ 308
Post-modification Outstanding Recorded Investment	$ 219	$ 220
Prior-Year accruing
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	3,045	3,049
Pre-modification Outstanding Recorded Investment	$ 160	$ 160
Post-modification Outstanding Recorded Investment	$ 121	$ 121
Prior-Year accruing | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	14	12
Pre-modification Outstanding Recorded Investment	$ 0	$ 0
Post-modification Outstanding Recorded Investment	$ 0	$ 0
Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	3,031	3,037
Pre-modification Outstanding Recorded Investment	$ 160	$ 160
Post-modification Outstanding Recorded Investment	$ 122	$ 121
Nonperforming financial instruments
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	1,340	1,380
Pre-modification Outstanding Recorded Investment	$ 143	$ 148
Post-modification Outstanding Recorded Investment	$ 98	$ 99
Nonperforming financial instruments | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	41	39
Pre-modification Outstanding Recorded Investment	$ 75	$ 80
Post-modification Outstanding Recorded Investment	$ 37	$ 39
Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	1,299	1,341
Pre-modification Outstanding Recorded Investment	$ 68	$ 68
Post-modification Outstanding Recorded Investment	$ 61	$ 60
Commercial and Industrial | Prior-Year accruing | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	13	11
Pre-modification Outstanding Recorded Investment	$ 0	$ 0
Post-modification Outstanding Recorded Investment	$ 0	$ 0
Commercial and Industrial | Nonperforming financial instruments | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	37	36
Pre-modification Outstanding Recorded Investment	$ 25	$ 30
Post-modification Outstanding Recorded Investment	$ 14	$ 14
Commercial mortgage | Prior-Year accruing | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	1	1
Pre-modification Outstanding Recorded Investment	$ 0	$ 0
Post-modification Outstanding Recorded Investment	$ 0	$ 0
Commercial mortgage | Nonperforming financial instruments | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	4	3
Pre-modification Outstanding Recorded Investment	$ 50	$ 50
Post-modification Outstanding Recorded Investment	$ 23	$ 25
Commercial real estate loans | Prior-Year accruing | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	1	1
Pre-modification Outstanding Recorded Investment	$ 0	$ 0
Post-modification Outstanding Recorded Investment	$ 0	$ 0
Commercial real estate loans | Nonperforming financial instruments | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	4	3
Pre-modification Outstanding Recorded Investment	$ 50	$ 50
Post-modification Outstanding Recorded Investment	$ 23	$ 25
Real estate — residential mortgage | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	463	455
Pre-modification Outstanding Recorded Investment	$ 41	$ 39
Post-modification Outstanding Recorded Investment	$ 35	$ 33
Real estate — residential mortgage | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	223	220
Pre-modification Outstanding Recorded Investment	$ 27	$ 26
Post-modification Outstanding Recorded Investment	$ 25	$ 24
Home equity loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	1,615	1,628
Pre-modification Outstanding Recorded Investment	$ 97	$ 97
Post-modification Outstanding Recorded Investment	$ 75	$ 75
Home equity loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	514	531
Pre-modification Outstanding Recorded Investment	$ 35	$ 36
Post-modification Outstanding Recorded Investment	$ 31	$ 31
Consumer direct loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	226	236
Pre-modification Outstanding Recorded Investment	$ 4	$ 5
Post-modification Outstanding Recorded Investment	$ 3	$ 3
Consumer direct loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	208	207
Pre-modification Outstanding Recorded Investment	$ 2	$ 3
Post-modification Outstanding Recorded Investment	$ 2	$ 2
Credit cards | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	599	579
Pre-modification Outstanding Recorded Investment	$ 4	$ 4
Post-modification Outstanding Recorded Investment	$ 2	$ 2
Credit cards | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	332	360
Pre-modification Outstanding Recorded Investment	$ 2	$ 2
Post-modification Outstanding Recorded Investment	$ 2	$ 2
Consumer indirect loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	128	139
Pre-modification Outstanding Recorded Investment	$ 14	$ 15
Post-modification Outstanding Recorded Investment	$ 7	$ 8
Consumer indirect loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	22	23
Pre-modification Outstanding Recorded Investment	$ 2	$ 1
Post-modification Outstanding Recorded Investment	$ 1	$ 1