Finance Receivables and Loans, Net (Past Due Financing Receivables and Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	$ 2,452	$ 3,151
Financing receivable, recorded investment, current	127,603	126,775
Total finance receivables and loans	130,055	129,926	$ 125,327
Consumer portfolio segment | Consumer loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	2,361	3,098
Financing receivable, recorded investment, current	86,850	84,142
Total finance receivables and loans	89,211	87,240
Consumer portfolio segment | Automobile loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	2,214	2,940
Financing receivable, recorded investment, current	69,339	67,599
Total finance receivables and loans	71,553	70,539	69,318
Consumer portfolio segment | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	147	158
Financing receivable, recorded investment, current	17,511	16,543
Total finance receivables and loans	17,658	16,701	14,683
Consumer portfolio segment | Mortgage Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	69	76
Financing receivable, recorded investment, current	16,156	15,079
Total finance receivables and loans	16,225	15,155
Consumer portfolio segment | Mortgage - Legacy
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	78	82
Financing receivable, recorded investment, current	1,355	1,464
Total finance receivables and loans	1,433	1,546
Commercial portfolio segment | Commercial loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	91	53
Financing receivable, recorded investment, current	40,753	42,633
Total finance receivables and loans	40,844	42,686	$ 41,326
Commercial portfolio segment | Commercial and industrial automotive
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	87	32
Financing receivable, recorded investment, current	31,472	33,640
Total finance receivables and loans	31,559	33,672
Commercial portfolio segment | Commercial and industrial other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	2	20
Financing receivable, recorded investment, current	4,514	4,185
Total finance receivables and loans	4,516	4,205
Commercial portfolio segment | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	2	1
Financing receivable, recorded investment, current	4,767	4,808
Total finance receivables and loans	4,769	4,809
Financing receivables, 30 to 59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	1,659	2,204
Financing receivables, 30 to 59 days past due | Consumer portfolio segment | Consumer loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	1,658	2,204
Financing receivables, 30 to 59 days past due | Consumer portfolio segment | Automobile loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	1,575	2,107
Financing receivables, 30 to 59 days past due | Consumer portfolio segment | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	83	97
Financing receivables, 30 to 59 days past due | Consumer portfolio segment | Mortgage Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	52	67
Financing receivables, 30 to 59 days past due | Consumer portfolio segment | Mortgage - Legacy
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	31	30
Financing receivables, 30 to 59 days past due | Commercial portfolio segment | Commercial loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	1	0
Financing receivables, 30 to 59 days past due | Commercial portfolio segment | Commercial and industrial automotive
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	1	0
Financing receivables, 30 to 59 days past due | Commercial portfolio segment | Commercial and industrial other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	0
Financing receivables, 30 to 59 days past due | Commercial portfolio segment | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	0
Financing receivables, 60 to 89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	406	557
Financing receivables, 60 to 89 days past due | Consumer portfolio segment | Consumer loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	398	552
Financing receivables, 60 to 89 days past due | Consumer portfolio segment | Automobile loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	379	537
Financing receivables, 60 to 89 days past due | Consumer portfolio segment | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	19	15
Financing receivables, 60 to 89 days past due | Consumer portfolio segment | Mortgage Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	8	5
Financing receivables, 60 to 89 days past due | Consumer portfolio segment | Mortgage - Legacy
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	11	10
Financing receivables, 60 to 89 days past due | Commercial portfolio segment | Commercial loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	8	5
Financing receivables, 60 to 89 days past due | Commercial portfolio segment | Commercial and industrial automotive
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	8	1
Financing receivables, 60 to 89 days past due | Commercial portfolio segment | Commercial and industrial other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	4
Financing receivables, 60 to 89 days past due | Commercial portfolio segment | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	0
Financing receivables, equal to greater than 90 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	387	390
Financing receivables, equal to greater than 90 days past due | Consumer portfolio segment | Consumer loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	305	342
Financing receivables, equal to greater than 90 days past due | Consumer portfolio segment | Automobile loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	260	296
Financing receivables, equal to greater than 90 days past due | Consumer portfolio segment | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	45	46
Financing receivables, equal to greater than 90 days past due | Consumer portfolio segment | Mortgage Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	9	4
Financing receivables, equal to greater than 90 days past due | Consumer portfolio segment | Mortgage - Legacy
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	36	42
Financing receivables, equal to greater than 90 days past due | Commercial portfolio segment | Commercial loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	82	48
Financing receivables, equal to greater than 90 days past due | Commercial portfolio segment | Commercial and industrial automotive
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	78	31
Financing receivables, equal to greater than 90 days past due | Commercial portfolio segment | Commercial and industrial other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	2	16
Financing receivables, equal to greater than 90 days past due | Commercial portfolio segment | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	$ 2	$ 1