Asset Quality - Breakdown of Nonperforming TDRs by Loans Category (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) SecurityLoan	Mar. 31, 2018 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	6,147	6,084
Pre-modification Outstanding Recorded Investment	$ 460	$ 491
Post-modification Outstanding Recorded Investment	$ 365	$ 399
Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	3,626	3,021
Pre-modification Outstanding Recorded Investment	$ 214	$ 195
Post-modification Outstanding Recorded Investment	$ 167	$ 152
Prior-Year Accruing [Member] | Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	10	13
Pre-modification Outstanding Recorded Investment	$ 38	$ 37
Post-modification Outstanding Recorded Investment	$ 31	$ 32
Prior-Year Accruing [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1	2
Pre-modification Outstanding Recorded Investment	$ 0	$ 0
Post-modification Outstanding Recorded Investment	$ 0	$ 0
Prior-Year Accruing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	3,616	3,008
Pre-modification Outstanding Recorded Investment	$ 176	$ 158
Post-modification Outstanding Recorded Investment	$ 136	$ 120
Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,521	3,063
Pre-modification Outstanding Recorded Investment	$ 246	$ 296
Post-modification Outstanding Recorded Investment	$ 198	$ 247
Nonperforming [Member] | Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	34	41
Pre-modification Outstanding Recorded Investment	$ 155	$ 187
Post-modification Outstanding Recorded Investment	$ 115	$ 147
Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,487	3,022
Pre-modification Outstanding Recorded Investment	$ 91	$ 109
Post-modification Outstanding Recorded Investment	$ 83	$ 100
Commercial and Industrial [Member] | Prior-Year Accruing [Member] | Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	9	11
Pre-modification Outstanding Recorded Investment	$ 38	$ 37
Post-modification Outstanding Recorded Investment	$ 31	$ 32
Commercial and Industrial [Member] | Prior-Year Accruing [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1	2
Pre-modification Outstanding Recorded Investment	$ 0	$ 0
Post-modification Outstanding Recorded Investment	$ 0	$ 0
Commercial and Industrial [Member] | Nonperforming [Member] | Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	27	35
Pre-modification Outstanding Recorded Investment	$ 89	$ 121
Post-modification Outstanding Recorded Investment	$ 57	$ 85
Commercial Real Estate: Commercial Mortgage [Member] | Nonperforming [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	7	6
Pre-modification Outstanding Recorded Investment	$ 66	$ 66
Post-modification Outstanding Recorded Investment	$ 58	$ 62
Commercial Real Estate Loans [Member] | Nonperforming [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	7	6
Pre-modification Outstanding Recorded Investment	$ 66	$ 66
Post-modification Outstanding Recorded Investment	$ 58	$ 62
Real Estate - Residential Mortgage [Member] | Prior-Year Accruing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	481	491
Pre-modification Outstanding Recorded Investment	$ 35	$ 36
Post-modification Outstanding Recorded Investment	$ 30	$ 30
Real Estate - Residential Mortgage [Member] | Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	284	281
Pre-modification Outstanding Recorded Investment	$ 20	$ 21
Post-modification Outstanding Recorded Investment	$ 18	$ 20
Home Equity Loans [Member] | Prior-Year Accruing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,648	1,403
Pre-modification Outstanding Recorded Investment	$ 96	$ 82
Post-modification Outstanding Recorded Investment	$ 79	$ 64
Home Equity Loans [Member] | Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	884	1,142
Pre-modification Outstanding Recorded Investment	$ 52	$ 66
Post-modification Outstanding Recorded Investment	$ 49	$ 63
Consumer Direct Loans [Member] | Prior-Year Accruing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	136	79
Pre-modification Outstanding Recorded Investment	$ 5	$ 4
Post-modification Outstanding Recorded Investment	$ 3	$ 3
Consumer Direct Loans [Member] | Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	120	171
Pre-modification Outstanding Recorded Investment	$ 2	$ 2
Post-modification Outstanding Recorded Investment	$ 1	$ 1
Consumer Credit Card [Member] | Prior-Year Accruing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	598	479
Pre-modification Outstanding Recorded Investment	$ 3	$ 3
Post-modification Outstanding Recorded Investment	$ 1	$ 1
Consumer Credit Card [Member] | Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	225	330
Pre-modification Outstanding Recorded Investment	$ 1	$ 2
Post-modification Outstanding Recorded Investment	$ 1	$ 2
Consumer Indirect Loans [Member] | Prior-Year Accruing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	753	556
Pre-modification Outstanding Recorded Investment	$ 37	$ 33
Post-modification Outstanding Recorded Investment	$ 23	$ 22
Consumer Indirect Loans [Member] | Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	974	1,098
Pre-modification Outstanding Recorded Investment	$ 16	$ 18
Post-modification Outstanding Recorded Investment	$ 14	$ 14