Equity in Net Assets of Non-consolidated Affiliates - Summarized Financial Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Aug. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summarized Balance Sheet Data
Finance receivables, net		$ 16,555,000,000	$ 13,459,000,000
Total assets		19,368,000,000	16,198,000,000
Debt		13,618,000,000	9,349,000,000
Total liabilities		16,439,000,000	13,807,000,000
Summarized Operating Data
Finance charge income		1,246,000,000	1,053,000,000	$ 940,000,000
Provision for loan losses		21,000,000	(6,000,000)	18,000,000
Interest expense		523,000,000	337,000,000	257,000,000
Income before income taxes		696,000,000	661,000,000	570,000,000
Net income		522,000,000	496,000,000	428,000,000
Undistributed earnings of foreign subsidiaries		$ 138,000,000	$ 45,000,000
SAIC-GMAC [Member]
Summarized Operating Data
Ownership percentage		35.00%	35.00%
Cash dividends received		$ 0	$ 0	$ 129,000,000
Undistributed earnings of foreign subsidiaries		$ 498,000,000	$ 315,000,000
SAIC-GMF Leasing Co. LTD [Member]
Schedule of Equity Method Investments [Line Items]
Capital investments	$ 51,000,000
Summarized Operating Data
Ownership percentage	35.00%	35.00%	0.00%