Asset Quality - Consumer Loans by Refreshed FICO Score (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 86,038	$ 59,876	$ 57,381
Consumer Portfolio Segment Excluding PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	23,724	15,593
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,035	7,378
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,647	5,095
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,486	1,708
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,556	1,412
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	17,823	12,566
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,818	6,378
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,266	3,822
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,617	1,291
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,122	1,075
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,781	1,600
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	498	445
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	661	619
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	194	203
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	428	333
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,111	806
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	453	322
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	525	389
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	132	94
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1	1
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,009	621
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,266	233
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,195	265
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	543	120
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5	3
Consumer Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	405	11
Consumer Portfolio Segment, PCI [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	133	2
Consumer Portfolio Segment, PCI [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	129	3
Consumer Portfolio Segment, PCI [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	137	5
Consumer Portfolio Segment, PCI [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6	1
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	398	11
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	133	2
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	127	3
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	133	5
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5	1
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7	0
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	0
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4	0
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0