Finance Receivables and Loans, Net (Financing Receivable Credit Quality Indicators Commercial) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Finance receivables and loans, net	$ 118,028	$ 128,231	$ 128,609
Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	2,223
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,187
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,613
Financing Receivable, Originated Three Years before Latest Fiscal Year	1,372
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,049
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,000
Financing Receivable, Revolving	18,283
Converted to term loans	141
Finance receivables and loans, net	27,868	38,307	$ 38,528
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	930
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	279
Financing Receivable, Originated Two Years before Latest Fiscal Year	135
Financing Receivable, Originated Three Years before Latest Fiscal Year	167
Financing Receivable, Originated Four Years before Latest Fiscal Year	98
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	62
Financing Receivable, Revolving	16,215
Converted to term loans	0
Finance receivables and loans, net	17,886	28,332
Automotive loan | Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	865
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	250
Financing Receivable, Originated Two Years before Latest Fiscal Year	70
Financing Receivable, Originated Three Years before Latest Fiscal Year	98
Financing Receivable, Originated Four Years before Latest Fiscal Year	66
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	43
Financing Receivable, Revolving	14,083
Converted to term loans	0
Finance receivables and loans, net	15,475	25,235
Automotive loan | Special Mention | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	63
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	27
Financing Receivable, Originated Two Years before Latest Fiscal Year	65
Financing Receivable, Originated Three Years before Latest Fiscal Year	67
Financing Receivable, Originated Four Years before Latest Fiscal Year	32
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	19
Financing Receivable, Revolving	2,070
Converted to term loans	0
Finance receivables and loans, net	2,343
Automotive loan | Substandard | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	2
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	57
Converted to term loans	0
Finance receivables and loans, net	61
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	0
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	5
Converted to term loans	0
Finance receivables and loans, net	7
Other loan | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	472
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	828
Financing Receivable, Originated Two Years before Latest Fiscal Year	559
Financing Receivable, Originated Three Years before Latest Fiscal Year	551
Financing Receivable, Originated Four Years before Latest Fiscal Year	209
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	306
Financing Receivable, Revolving	2,068
Converted to term loans	138
Finance receivables and loans, net	5,131	5,014
Other loan | Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	412
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	658
Financing Receivable, Originated Two Years before Latest Fiscal Year	288
Financing Receivable, Originated Three Years before Latest Fiscal Year	276
Financing Receivable, Originated Four Years before Latest Fiscal Year	116
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	52
Financing Receivable, Revolving	1,721
Converted to term loans	79
Finance receivables and loans, net	3,602	4,225
Other loan | Special Mention | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	27
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	170
Financing Receivable, Originated Two Years before Latest Fiscal Year	271
Financing Receivable, Originated Three Years before Latest Fiscal Year	205
Financing Receivable, Originated Four Years before Latest Fiscal Year	93
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	129
Financing Receivable, Revolving	322
Converted to term loans	48
Finance receivables and loans, net	1,265
Other loan | Substandard | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	33
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	70
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	125
Financing Receivable, Revolving	25
Converted to term loans	11
Finance receivables and loans, net	264
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	821
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,080
Financing Receivable, Originated Two Years before Latest Fiscal Year	919
Financing Receivable, Originated Three Years before Latest Fiscal Year	654
Financing Receivable, Originated Four Years before Latest Fiscal Year	742
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	632
Financing Receivable, Revolving	0
Converted to term loans	3
Finance receivables and loans, net	4,851	4,961
Real estate-backed loan | Pass | Commercial portfolio segment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	789
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	937
Financing Receivable, Originated Two Years before Latest Fiscal Year	798
Financing Receivable, Originated Three Years before Latest Fiscal Year	582
Financing Receivable, Originated Four Years before Latest Fiscal Year	656
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	569
Financing Receivable, Revolving	0
Converted to term loans	3
Finance receivables and loans, net	4,334	$ 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	32
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	143
Financing Receivable, Originated Two Years before Latest Fiscal Year	121
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	55
Financing Receivable, Revolving	0
Converted to term loans	0
Finance receivables and loans, net	504
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