Loans and Related Allowance for Credit Losses (Credit Quality Indicators for Automobile, Credit Card, Education and Other Consumer Loan Classes) (Details) $ in Millions	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 258,236	$ 239,843
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	2,508
Financing receivable, originated in 2019	6,768
Financing receivable, originated in 2018	3,712
Financing receivable, originated in 2017	1,879
Financing receivable, originated in 2016	954
Prior	336
Total Loans	16,157	$ 16,754
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	1,816
Financing receivable, originated in 2019	3,802
Financing receivable, originated in 2018	1,814
Financing receivable, originated in 2017	1,042
Financing receivable, originated in 2016	606
Prior	201
Total Loans	9,281	$ 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	561
Financing receivable, originated in 2019	1,868
Financing receivable, originated in 2018	1,062
Financing receivable, originated in 2017	481
Financing receivable, originated in 2016	207
Prior	75
Total Loans	4,254	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	73
Financing receivable, originated in 2019	445
Financing receivable, originated in 2018	257
Financing receivable, originated in 2017	104
Financing receivable, originated in 2016	39
Prior	15
Total Loans	933	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	58
Financing receivable, originated in 2019	653
Financing receivable, originated in 2018	579
Financing receivable, originated in 2017	252
Financing receivable, originated in 2016	102
Prior	45
Total Loans	1,689	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	6,473
Revolving Loans Converted to Term	102
Total Loans	6,575	$ 7,308
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	3,395
Revolving Loans Converted to Term	11
Total Loans	3,406	$ 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	2,152
Revolving Loans Converted to Term	30
Total Loans	2,182	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	378
Revolving Loans Converted to Term	12
Total Loans	390	419
Credit Card [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	462
Revolving Loans Converted to Term	46
Total Loans	508	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	86
Revolving Loans Converted to Term	3
Total Loans	89	152
Education [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	36
Financing receivable, originated in 2019	172
Financing receivable, originated in 2018	145
Financing receivable, originated in 2017	110
Financing receivable, originated in 2016	84
Prior	2,585
Total Loans	3,132	3,336
Education [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	18
Financing receivable, originated in 2019	113
Financing receivable, originated in 2018	145
Financing receivable, originated in 2017	110
Financing receivable, originated in 2016	84
Prior	827
Total Loans	1,297	$ 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	13
Financing receivable, originated in 2019	90
Financing receivable, originated in 2018	119
Financing receivable, originated in 2017	92
Financing receivable, originated in 2016	75
Prior	674
Total Loans	1,063	$ 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	3
Financing receivable, originated in 2019	12
Financing receivable, originated in 2018	16
Financing receivable, originated in 2017	10
Financing receivable, originated in 2016	7
Prior	112
Total Loans	160	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
Prior	18
Total Loans	22	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 2018	1
Financing receivable, originated in 2017	1
Financing receivable, originated in 2016	1
Prior	22
Total Loans	25	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	2
Financing receivable, originated in 2019	10
Financing receivable, originated in 2018	7
Financing receivable, originated in 2017	6
Financing receivable, originated in 2016	1
Prior	1
Total Loans	27	15
Education [Member] | Other Internal Credit Metrics [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	18
Financing receivable, originated in 2019	59
Prior	1,758
Total Loans	1,835	1,933
Other Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	455
Financing receivable, originated in 2019	1,030
Financing receivable, originated in 2018	425
Financing receivable, originated in 2017	138
Financing receivable, originated in 2016	99
Prior	197
Revolving Loans	2,478
Revolving Loans Converted to Term	7
Total Loans	4,829	4,937
Other Consumer [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	435
Financing receivable, originated in 2019	957
Financing receivable, originated in 2018	379
Financing receivable, originated in 2017	106
Financing receivable, originated in 2016	32
Prior	116
Revolving Loans	419
Revolving Loans Converted to Term	3
Total Loans	2,447	$ 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	297
Financing receivable, originated in 2019	545
Financing receivable, originated in 2018	188
Financing receivable, originated in 2017	60
Financing receivable, originated in 2016	19
Prior	80
Revolving Loans	212
Revolving Loans Converted to Term	1
Total Loans	1,402	$ 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	117
Financing receivable, originated in 2019	313
Financing receivable, originated in 2018	134
Financing receivable, originated in 2017	31
Financing receivable, originated in 2016	9
Prior	23
Revolving Loans	143
Revolving Loans Converted to Term	1
Total Loans	771	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	13
Financing receivable, originated in 2019	51
Financing receivable, originated in 2018	24
Financing receivable, originated in 2017	5
Financing receivable, originated in 2016	1
Prior	4
Revolving Loans	22
Total Loans	120	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	8
Financing receivable, originated in 2019	48
Financing receivable, originated in 2018	33
Financing receivable, originated in 2017	10
Financing receivable, originated in 2016	3
Prior	7
Revolving Loans	36
Revolving Loans Converted to Term	1
Total Loans	146	143
Other Consumer [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Prior	2
Revolving Loans	6
Total Loans	8	27
Other Consumer [Member] | Other Internal Credit Metrics [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	20
Financing receivable, originated in 2019	73
Financing receivable, originated in 2018	46
Financing receivable, originated in 2017	32
Financing receivable, originated in 2016	67
Prior	81
Revolving Loans	2,059
Revolving Loans Converted to Term	4
Total Loans	$ 2,382	$ 2,371