Asset Quality - Breakdown of Nonperforming TDRs by Loans Category (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) SecurityLoan	Dec. 31, 2017 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	6,084	5,184
Pre-modification Outstanding Recorded Investment	$ 491	$ 398
Post-modification Outstanding Recorded Investment	$ 399	$ 317
Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	3,021	2,562
Pre-modification Outstanding Recorded Investment	$ 195	$ 171
Post-modification Outstanding Recorded Investment	$ 152	$ 128
Nonperforming [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	3,063	2,622
Pre-modification Outstanding Recorded Investment	$ 296	$ 227
Post-modification Outstanding Recorded Investment	$ 247	$ 189
Commercial Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	13	4
Pre-modification Outstanding Recorded Investment	$ 37	$ 30
Post-modification Outstanding Recorded Investment	$ 32	$ 13
Commercial Loans [Member] | Commercial, Financial and Agricultural [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	11	4
Pre-modification Outstanding Recorded Investment	$ 37	$ 30
Post-modification Outstanding Recorded Investment	$ 32	$ 13
Commercial Loans [Member] | Nonperforming [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	41	28
Pre-modification Outstanding Recorded Investment	$ 187	$ 125
Post-modification Outstanding Recorded Investment	$ 147	$ 98
Commercial Loans [Member] | Nonperforming [Member] | Commercial, Financial and Agricultural [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	35	20
Pre-modification Outstanding Recorded Investment	$ 121	$ 109
Post-modification Outstanding Recorded Investment	$ 85	$ 86
Commercial Real Estate Portfolio Segment [Member] | Commercial, Financial and Agricultural [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2	0
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] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	6	8
Pre-modification Outstanding Recorded Investment	$ 66	$ 16
Post-modification Outstanding Recorded Investment	$ 62	$ 12
Commercial Real Estate Portfolio Segment [Member] | Nonperforming [Member] | Commercial Real Estate Loans [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	6	8
Pre-modification Outstanding Recorded Investment	$ 66	$ 16
Post-modification Outstanding Recorded Investment	$ 62	$ 12
Consumer Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	3,008	2,558
Pre-modification Outstanding Recorded Investment	$ 158	$ 141
Post-modification Outstanding Recorded Investment	$ 120	$ 115
Consumer Loans [Member] | Real Estate - Residential Mortgage [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	491	484
Pre-modification Outstanding Recorded Investment	$ 36	$ 31
Post-modification Outstanding Recorded Investment	$ 30	$ 31
Consumer Loans [Member] | Home Equity Loan [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,403	1,276
Pre-modification Outstanding Recorded Investment	$ 82	$ 75
Post-modification Outstanding Recorded Investment	$ 64	$ 59
Consumer Loans [Member] | Consumer Direct Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	79	48
Pre-modification Outstanding Recorded Investment	$ 4	$ 3
Post-modification Outstanding Recorded Investment	$ 3	$ 2
Consumer Loans [Member] | Consumer Credit Card [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	479	430
Pre-modification Outstanding Recorded Investment	$ 3	$ 1
Post-modification Outstanding Recorded Investment	$ 1	$ 1
Consumer Loans [Member] | Consumer Indirect Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	556	320
Pre-modification Outstanding Recorded Investment	$ 33	$ 31
Post-modification Outstanding Recorded Investment	$ 22	$ 22
Consumer Loans [Member] | Nonperforming [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	3,022	2,594
Pre-modification Outstanding Recorded Investment	$ 109	$ 102
Post-modification Outstanding Recorded Investment	$ 100	$ 91
Consumer Loans [Member] | Nonperforming [Member] | Real Estate - Residential Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	281	308
Pre-modification Outstanding Recorded Investment	$ 21	$ 18
Post-modification Outstanding Recorded Investment	$ 20	$ 18
Consumer Loans [Member] | Nonperforming [Member] | Home Equity Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,142	1,025
Pre-modification Outstanding Recorded Investment	$ 66	$ 64
Post-modification Outstanding Recorded Investment	$ 63	$ 57
Consumer Loans [Member] | Nonperforming [Member] | Consumer Direct Loans [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	171	114
Pre-modification Outstanding Recorded Investment	$ 2	$ 2
Post-modification Outstanding Recorded Investment	$ 1	$ 2
Consumer Loans [Member] | Nonperforming [Member] | Consumer Credit Card [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	330	322
Pre-modification Outstanding Recorded Investment	$ 2	$ 2
Post-modification Outstanding Recorded Investment	$ 2	$ 1
Consumer Loans [Member] | Nonperforming [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,098	825
Pre-modification Outstanding Recorded Investment	$ 18	$ 16
Post-modification Outstanding Recorded Investment	$ 14	$ 13