Asset Quality - Breakdown of Nonperforming TDRs by Loans Category (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) SecurityLoan	Dec. 31, 2018 USD ($) SecurityLoan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	6,212	6,084
Pre-modification Outstanding Recorded Investment	$ 425	$ 491
Post-modification Outstanding Recorded Investment	$ 347	$ 399
Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	3,590	3,021
Pre-modification Outstanding Recorded Investment	$ 211	$ 195
Post-modification Outstanding Recorded Investment	$ 164	$ 152
Nonperforming [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	2,622	3,063
Pre-modification Outstanding Recorded Investment	$ 214	$ 296
Post-modification Outstanding Recorded Investment	$ 183	$ 247
Commercial Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	7	13
Pre-modification Outstanding Recorded Investment	$ 30	$ 37
Post-modification Outstanding Recorded Investment	$ 25	$ 32
Commercial Loans [Member] | Commercial, Financial and Agricultural [Member] | Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	6	11
Pre-modification Outstanding Recorded Investment	$ 30	$ 37
Post-modification Outstanding Recorded Investment	$ 25	$ 32
Commercial Loans [Member] | Nonperforming [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	57	41
Pre-modification Outstanding Recorded Investment	$ 136	$ 187
Post-modification Outstanding Recorded Investment	$ 111	$ 147
Commercial Loans [Member] | Nonperforming [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	51	35
Pre-modification Outstanding Recorded Investment	$ 72	$ 121
Post-modification Outstanding Recorded Investment	$ 53	$ 85
Commercial Real Estate Portfolio Segment [Member] | Commercial, Financial and Agricultural [Member] | Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	1	2
Pre-modification Outstanding Recorded Investment	$ 0	$ 0
Post-modification Outstanding Recorded Investment	$ 0	$ 0
Commercial Real Estate Portfolio Segment [Member] | Nonperforming [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	6	6
Pre-modification Outstanding Recorded Investment	$ 64	$ 66
Post-modification Outstanding Recorded Investment	$ 58	$ 62
Commercial Real Estate Portfolio Segment [Member] | Nonperforming [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	6	6
Pre-modification Outstanding Recorded Investment	$ 64	$ 66
Post-modification Outstanding Recorded Investment	$ 58	$ 62
Consumer Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	3,583	3,008
Pre-modification Outstanding Recorded Investment	$ 181	$ 158
Post-modification Outstanding Recorded Investment	$ 139	$ 120
Consumer Loans [Member] | Real Estate - Residential Mortgage [Member] | Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	493	491
Pre-modification Outstanding Recorded Investment	$ 37	$ 36
Post-modification Outstanding Recorded Investment	$ 31	$ 30
Consumer Loans [Member] | Home Equity Loan [Member] | Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	1,751	1,403
Pre-modification Outstanding Recorded Investment	$ 104	$ 82
Post-modification Outstanding Recorded Investment	$ 84	$ 64
Consumer Loans [Member] | Consumer Direct Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	139	79
Pre-modification Outstanding Recorded Investment	$ 4	$ 4
Post-modification Outstanding Recorded Investment	$ 3	$ 3
Consumer Loans [Member] | Consumer Credit Card [Member] | Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	486	479
Pre-modification Outstanding Recorded Investment	$ 3	$ 3
Post-modification Outstanding Recorded Investment	$ 1	$ 1
Consumer Loans [Member] | Consumer Indirect Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	714	556
Pre-modification Outstanding Recorded Investment	$ 33	$ 33
Post-modification Outstanding Recorded Investment	$ 20	$ 22
Consumer Loans [Member] | Nonperforming [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	2,565	3,022
Pre-modification Outstanding Recorded Investment	$ 78	$ 109
Post-modification Outstanding Recorded Investment	$ 72	$ 100
Consumer Loans [Member] | Nonperforming [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	181	281
Pre-modification Outstanding Recorded Investment	$ 13	$ 21
Post-modification Outstanding Recorded Investment	$ 11	$ 20
Consumer Loans [Member] | Nonperforming [Member] | Home Equity Loan [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	713	1,142
Pre-modification Outstanding Recorded Investment	$ 42	$ 66
Post-modification Outstanding Recorded Investment	$ 41	$ 63
Consumer Loans [Member] | Nonperforming [Member] | Consumer Direct Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	172	171
Pre-modification Outstanding Recorded Investment	$ 2	$ 2
Post-modification Outstanding Recorded Investment	$ 2	$ 1
Consumer Loans [Member] | Nonperforming [Member] | Consumer Credit Card [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	368	330
Pre-modification Outstanding Recorded Investment	$ 2	$ 2
Post-modification Outstanding Recorded Investment	$ 2	$ 2
Consumer Loans [Member] | Nonperforming [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	1,131	1,098
Pre-modification Outstanding Recorded Investment	$ 19	$ 18
Post-modification Outstanding Recorded Investment	$ 16	$ 14