Finance Receivables and Loans, Net (Financing Receivable Credit Quality Indicators Commercial) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Finance receivables and loans, net	$ 118,234	$ 128,231	$ 129,210
Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1,668
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,263
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,691
Financing Receivable, Originated Three Years before Latest Fiscal Year	1,432
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,114
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,284
Financing Receivable, Revolving	18,293
Converted to term loans	124
Finance receivables and loans, net	27,869	38,307	$ 38,512
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	847
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	301
Financing Receivable, Originated Two Years before Latest Fiscal Year	162
Financing Receivable, Originated Three Years before Latest Fiscal Year	179
Financing Receivable, Originated Four Years before Latest Fiscal Year	105
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	92
Financing Receivable, Revolving	16,069
Converted to term loans	0
Finance receivables and loans, net	17,755	28,332
Automotive loan | Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	785
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	281
Financing Receivable, Originated Two Years before Latest Fiscal Year	107
Financing Receivable, Originated Three Years before Latest Fiscal Year	112
Financing Receivable, Originated Four Years before Latest Fiscal Year	72
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	78
Financing Receivable, Revolving	13,802
Converted to term loans	0
Finance receivables and loans, net	15,237	25,235
Automotive loan | Special Mention | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	61
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	18
Financing Receivable, Originated Two Years before Latest Fiscal Year	54
Financing Receivable, Originated Three Years before Latest Fiscal Year	65
Financing Receivable, Originated Four Years before Latest Fiscal Year	33
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	14
Financing Receivable, Revolving	2,157
Converted to term loans	0
Finance receivables and loans, net	2,402
Automotive loan | Substandard | 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	2
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	82
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	28
Converted to term loans	0
Finance receivables and loans, net	31
Other loan | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	419
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	833
Financing Receivable, Originated Two Years before Latest Fiscal Year	594
Financing Receivable, Originated Three Years before Latest Fiscal Year	562
Financing Receivable, Originated Four Years before Latest Fiscal Year	211
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	350
Financing Receivable, Revolving	2,224
Converted to term loans	122
Finance receivables and loans, net	5,315	5,014
Other loan | Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	419
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	631
Financing Receivable, Originated Two Years before Latest Fiscal Year	338
Financing Receivable, Originated Three Years before Latest Fiscal Year	299
Financing Receivable, Originated Four Years before Latest Fiscal Year	117
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	98
Financing Receivable, Revolving	1,912
Converted to term loans	73
Finance receivables and loans, net	3,887	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	202
Financing Receivable, Originated Two Years before Latest Fiscal Year	256
Financing Receivable, Originated Three Years before Latest Fiscal Year	225
Financing Receivable, Originated Four Years before Latest Fiscal Year	94
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	119
Financing Receivable, Revolving	293
Converted to term loans	38
Finance receivables and loans, net	1,227
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	38
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	133
Financing Receivable, Revolving	19
Converted to term loans	11
Finance receivables and loans, net	201
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	0
Financing Receivable, Revolving	0
Converted to term loans	0
Finance receivables and loans, net	0
Real estate-backed loan | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	402
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,129
Financing Receivable, Originated Two Years before Latest Fiscal Year	935
Financing Receivable, Originated Three Years before Latest Fiscal Year	691
Financing Receivable, Originated Four Years before Latest Fiscal Year	798
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	842
Financing Receivable, Revolving	0
Converted to term loans	2
Finance receivables and loans, net	4,799	4,961
Real estate-backed loan | Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	386
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,058
Financing Receivable, Originated Two Years before Latest Fiscal Year	873
Financing Receivable, Originated Three Years before Latest Fiscal Year	619
Financing Receivable, Originated Four Years before Latest Fiscal Year	712
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	803
Financing Receivable, Revolving	0
Converted to term loans	2
Finance receivables and loans, net	4,453	$ 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	16
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	71
Financing Receivable, Originated Two Years before Latest Fiscal Year	62
Financing Receivable, Originated Three Years before Latest Fiscal Year	69
Financing Receivable, Originated Four Years before Latest Fiscal Year	84
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	31
Financing Receivable, Revolving	0
Converted to term loans	0
Finance receivables and loans, net	333
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	7
Financing Receivable, Revolving	0
Converted to term loans	0
Finance receivables and loans, net	10
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	1
Financing Receivable, Revolving	0
Converted to term loans	0
Finance receivables and loans, net	$ 3