Finance Receivables and Loans, Net (Past Due Financing Receivables and Loans) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	$ 3,151	$ 2,967
Financing receivable, recorded investment, current	126,775	119,926
Total finance receivables and loans	129,926	122,893
Consumer portfolio segment | Consumer loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	3,098	2,959
Financing receivable, recorded investment, current	84,142	78,862
Total finance receivables and loans	87,240	81,821
Consumer portfolio segment | Automobile loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	2,940	2,740
Financing receivable, recorded investment, current	67,599	65,331
Total finance receivables and loans	70,539	68,071
Consumer portfolio segment | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	158	219
Financing receivable, recorded investment, current	16,543	13,531
Total finance receivables and loans	16,701	13,750
Consumer portfolio segment | Mortgage Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	76	89
Financing receivable, recorded investment, current	15,079	11,568
Total finance receivables and loans	15,155	11,657
Consumer portfolio segment | Mortgage - Legacy
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	82	130
Financing receivable, recorded investment, current	1,464	1,963
Total finance receivables and loans	1,546	2,093
Commercial portfolio segment | Commercial loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	53	8
Financing receivable, recorded investment, current	42,633	41,064
Total finance receivables and loans	42,686	41,072
Commercial portfolio segment | Commercial and industrial automotive
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	32	8
Financing receivable, recorded investment, current	33,640	33,017
Total finance receivables and loans	33,672	33,025
Commercial portfolio segment | Commercial and industrial other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	20	0
Financing receivable, recorded investment, current	4,185	3,887
Total finance receivables and loans	4,205	3,887
Commercial portfolio segment | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	1	0
Financing receivable, recorded investment, current	4,808	4,160
Total finance receivables and loans	4,809	4,160
Financing receivables, 30 to 59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, recorded investment, past due	2,204	2,102
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	2,204	2,097
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	2,107	1,994
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	97	103
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	67	60
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	30	43
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	0	5
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	0	5
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	557	514
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	552	514
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	537	478
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	15	36
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	5	11
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	10	25
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	5	0
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	1	0
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	4	0
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	390	351
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	342	348
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	296	268
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	46	80
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	4	18
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	42	62
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	48	3
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	31	3
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	16	0
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	$ 1	$ 0