Finance Receivables and Loans, Net Finance Receivables and Loans, Net (Financing Receivable Credit Quality Indicators Commercial) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Finance receivables and loans, net	$ 128,139	$ 128,231	$ 130,055
Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	503
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,278
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,825
Financing Receivable, Originated Three Years before Latest Fiscal Year	1,463
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,177
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,414
Financing Receivable, Revolving	29,250
Converted to term loans	163
Finance receivables and loans, net	38,073	38,307	$ 40,844
Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Finance receivables and loans, net		34,080
Automotive loan | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	106
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	318
Financing Receivable, Originated Two Years before Latest Fiscal Year	174
Financing Receivable, Originated Three Years before Latest Fiscal Year	181
Financing Receivable, Originated Four Years before Latest Fiscal Year	113
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	99
Financing Receivable, Revolving	26,403
Converted to term loans	0
Finance receivables and loans, net	27,394	28,332
Automotive loan | Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	105
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	302
Financing Receivable, Originated Two Years before Latest Fiscal Year	128
Financing Receivable, Originated Three Years before Latest Fiscal Year	121
Financing Receivable, Originated Four Years before Latest Fiscal Year	81
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	83
Financing Receivable, Revolving	22,885
Converted to term loans	0
Finance receivables and loans, net	23,705	25,235
Automotive loan | Special Mention | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	16
Financing Receivable, Originated Two Years before Latest Fiscal Year	45
Financing Receivable, Originated Three Years before Latest Fiscal Year	58
Financing Receivable, Originated Four Years before Latest Fiscal Year	32
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	16
Financing Receivable, Revolving	3,399
Converted to term loans	0
Finance receivables and loans, net	3,567
Automotive loan | Substandard | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0
Financing Receivable, Revolving	85
Converted to term loans	0
Finance receivables and loans, net	85
Automotive loan | Doubtful | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	1
Financing Receivable, Originated Three Years before Latest Fiscal Year	2
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0
Financing Receivable, Revolving	34
Converted to term loans	0
Finance receivables and loans, net	37
Other loan | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	178
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	855
Financing Receivable, Originated Two Years before Latest Fiscal Year	642
Financing Receivable, Originated Three Years before Latest Fiscal Year	577
Financing Receivable, Originated Four Years before Latest Fiscal Year	214
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	403
Financing Receivable, Revolving	2,847
Converted to term loans	162
Finance receivables and loans, net	5,878	5,014
Other loan | Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	178
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	808
Financing Receivable, Originated Two Years before Latest Fiscal Year	440
Financing Receivable, Originated Three Years before Latest Fiscal Year	310
Financing Receivable, Originated Four Years before Latest Fiscal Year	118
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	150
Financing Receivable, Revolving	2,605
Converted to term loans	118
Finance receivables and loans, net	4,727	4,225
Other loan | Special Mention | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	47
Financing Receivable, Originated Two Years before Latest Fiscal Year	202
Financing Receivable, Originated Three Years before Latest Fiscal Year	246
Financing Receivable, Originated Four Years before Latest Fiscal Year	96
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	97
Financing Receivable, Revolving	230
Converted to term loans	35
Finance receivables and loans, net	953
Other loan | Substandard | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	21
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	134
Financing Receivable, Revolving	10
Converted to term loans	9
Finance receivables and loans, net	174
Other loan | Doubtful | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	22
Financing Receivable, Revolving	2
Converted to term loans	0
Finance receivables and loans, net	24
Real estate-backed loan | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	219
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,105
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,009
Financing Receivable, Originated Three Years before Latest Fiscal Year	705
Financing Receivable, Originated Four Years before Latest Fiscal Year	850
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	912
Financing Receivable, Revolving	0
Converted to term loans	1
Finance receivables and loans, net	4,801	4,961
Real estate-backed loan | Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	204
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,046
Financing Receivable, Originated Two Years before Latest Fiscal Year	951
Financing Receivable, Originated Three Years before Latest Fiscal Year	647
Financing Receivable, Originated Four Years before Latest Fiscal Year	769
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	864
Financing Receivable, Revolving	0
Converted to term loans	1
Finance receivables and loans, net	4,482	$ 4,620
Real estate-backed loan | Special Mention | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	15
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	59
Financing Receivable, Originated Two Years before Latest Fiscal Year	58
Financing Receivable, Originated Three Years before Latest Fiscal Year	55
Financing Receivable, Originated Four Years before Latest Fiscal Year	79
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	43
Financing Receivable, Revolving	0
Converted to term loans	0
Finance receivables and loans, net	309
Real estate-backed loan | Substandard | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	3
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	3
Financing Receivable, Revolving	0
Converted to term loans	0
Finance receivables and loans, net	6
Real estate-backed loan | Doubtful | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	2
Financing Receivable, Revolving	0
Converted to term loans	0
Finance receivables and loans, net	$ 4