Loans (Credit Card and Other Consumer Loan Classes Asset Quality Indicators) (Details) $ in Millions	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 264,643	$ 239,843
Financing receivable, originated in 2020, % of total loans	4.60%
Financing receivable, originated in 2019, % of total loans	14.90%
Financing receivable, originated in 2018, % of total loans	9.80%
Financing receivable, originated in 2017, % of total loans	7.20%
Financing receivable, originated in 2016, % of total loans	5.20%
Prior, % of total loans	12.80%
Revolving Loans, % of total loans	45.50%
Revolving Loans Converted To Term, % of total loans	0.00%
Total Loans, % of total loans	100.00%
Automobile Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans		16,754
Automobile Loan [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	$ 1,928
Financing receivable, originated in 2019	7,400
Financing receivable, originated in 2018	4,119
Financing receivable, originated in 2017	2,140
Financing receivable, originated in 2016	1,147
Prior	460
Total Loans	$ 17,194	$ 16,754
Financing receivable, originated in 2020, % of total loans	11.20%
Financing receivable, originated in 2019, % of total loans	43.00%
Financing receivable, originated in 2018, % of total loans	24.00%
Financing receivable, originated in 2017, % of total loans	12.40%
Financing receivable, originated in 2016, % of total loans	6.70%
Prior, % of total loans	2.70%
Total Loans, % of total loans	100.00%
Weighted average updated FICO score		726
Automobile Loan [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	$ 1,586
Financing receivable, originated in 2019	4,090
Financing receivable, originated in 2018	1,955
Financing receivable, originated in 2017	1,164
Financing receivable, originated in 2016	725
Prior	275
Total Loans	9,795	$ 9,232
Automobile Loan [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	320
Financing receivable, originated in 2019	2,112
Financing receivable, originated in 2018	1,225
Financing receivable, originated in 2017	571
Financing receivable, originated in 2016	256
Prior	105
Total Loans	4,589	4,577
Automobile Loan [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	14
Financing receivable, originated in 2019	525
Financing receivable, originated in 2018	306
Financing receivable, originated in 2017	122
Financing receivable, originated in 2016	47
Prior	21
Total Loans	1,035	1,001
Automobile Loan [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	8
Financing receivable, originated in 2019	673
Financing receivable, originated in 2018	633
Financing receivable, originated in 2017	283
Financing receivable, originated in 2016	119
Prior	59
Total Loans	1,775	1,603
Automobile Loan [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans		341
Credit Card [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans		7,308
Credit Card [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	7,031
Revolving Loans Converted to Term	101
Total Loans	$ 7,132	$ 7,308
Revolving Loans, % of total loans	98.60%
Revolving Loans Converted To Term, % of total loans	1.40%
Total Loans, % of total loans	100.00%
Weighted average updated FICO score		724
Credit Card [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	$ 3,564
Revolving Loans Converted to Term	10
Total Loans	3,574	$ 3,867
Credit Card [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	2,370
Revolving Loans Converted to Term	27
Total Loans	2,397	2,326
Credit Card [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	442
Revolving Loans Converted to Term	12
Total Loans	454	419
Credit Card [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	547
Revolving Loans Converted to Term	49
Total Loans	596	544
Credit Card [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	108
Revolving Loans Converted to Term	3
Total Loans	111	152
Education [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	23
Financing receivable, originated in 2019	175
Financing receivable, originated in 2018	150
Financing receivable, originated in 2017	114
Financing receivable, originated in 2016	90
Prior	2,695
Total Loans	$ 3,247	3,336
Financing receivable, originated in 2020, % of total loans	0.70%
Financing receivable, originated in 2019, % of total loans	5.40%
Financing receivable, originated in 2018, % of total loans	4.60%
Financing receivable, originated in 2017, % of total loans	3.50%
Financing receivable, originated in 2016, % of total loans	2.80%
Prior, % of total loans	83.00%
Total Loans, % of total loans	100.00%
Education [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	$ 12
Financing receivable, originated in 2019	116
Financing receivable, originated in 2018	150
Financing receivable, originated in 2017	114
Financing receivable, originated in 2016	90
Prior	872
Total Loans	1,354	$ 1,403
Weighted average updated FICO score		773
Education [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	7
Financing receivable, originated in 2019	89
Financing receivable, originated in 2018	121
Financing receivable, originated in 2017	94
Financing receivable, originated in 2016	78
Prior	703
Total Loans	1,092	$ 1,139
Education [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	2
Financing receivable, originated in 2019	14
Financing receivable, originated in 2018	19
Financing receivable, originated in 2017	12
Financing receivable, originated in 2016	9
Prior	124
Total Loans	180	197
Education [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2019	1
Financing receivable, originated in 2018	2
Financing receivable, originated in 2017	1
Financing receivable, originated in 2016	1
Prior	20
Total Loans	25	25
Education [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2019	1
Financing receivable, originated in 2018	1
Financing receivable, originated in 2017	1
Financing receivable, originated in 2016	1
Prior	24
Total Loans	28	27
Education [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	3
Financing receivable, originated in 2019	11
Financing receivable, originated in 2018	7
Financing receivable, originated in 2017	6
Financing receivable, originated in 2016	1
Prior	1
Total Loans	29	15
Education [Member] | Other Internal Credit Metrics [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	11
Financing receivable, originated in 2019	59
Prior	1,823
Total Loans	1,893	1,933
Other Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	381
Financing receivable, originated in 2019	1,147
Financing receivable, originated in 2018	492
Financing receivable, originated in 2017	163
Financing receivable, originated in 2016	109
Prior	219
Revolving Loans	2,486
Revolving Loans Converted to Term	6
Total Loans	$ 5,003	4,937
Financing receivable, originated in 2020, % of total loans	7.60%
Financing receivable, originated in 2019, % of total loans	22.90%
Financing receivable, originated in 2018, % of total loans	9.80%
Financing receivable, originated in 2017, % of total loans	3.30%
Financing receivable, originated in 2016, % of total loans	2.20%
Prior, % of total loans	4.40%
Revolving Loans, % of total loans	49.70%
Revolving Loans Converted To Term, % of total loans	0.10%
Total Loans, % of total loans	100.00%
Other Consumer [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	$ 367
Financing receivable, originated in 2019	1,073
Financing receivable, originated in 2018	443
Financing receivable, originated in 2017	129
Financing receivable, originated in 2016	44
Prior	131
Revolving Loans	468
Revolving Loans Converted to Term	3
Total Loans	2,658	$ 2,566
Weighted average updated FICO score		727
Other Consumer [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	218
Financing receivable, originated in 2019	623
Financing receivable, originated in 2018	219
Financing receivable, originated in 2017	71
Financing receivable, originated in 2016	25
Prior	90
Revolving Loans	230
Revolving Loans Converted to Term	1
Total Loans	1,477	$ 1,421
Other Consumer [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	126
Financing receivable, originated in 2019	349
Financing receivable, originated in 2018	158
Financing receivable, originated in 2017	40
Financing receivable, originated in 2016	13
Prior	26
Revolving Loans	162
Revolving Loans Converted to Term	1
Total Loans	875	843
Other Consumer [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	17
Financing receivable, originated in 2019	56
Financing receivable, originated in 2018	29
Financing receivable, originated in 2017	6
Financing receivable, originated in 2016	2
Prior	4
Revolving Loans	26
Total Loans	140	132
Other Consumer [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	5
Financing receivable, originated in 2019	45
Financing receivable, originated in 2018	37
Financing receivable, originated in 2017	12
Financing receivable, originated in 2016	4
Prior	9
Revolving Loans	44
Revolving Loans Converted to Term	1
Total Loans	157	143
Other Consumer [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	1
Prior	2
Revolving Loans	6
Total Loans	9	27
Other Consumer [Member] | Other Internal Credit Metrics [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	14
Financing receivable, originated in 2019	74
Financing receivable, originated in 2018	49
Financing receivable, originated in 2017	34
Financing receivable, originated in 2016	65
Prior	88
Revolving Loans	2,018
Revolving Loans Converted to Term	3
Total Loans	$ 2,345	$ 2,371