Equity in Net Assets of Non-consolidated Affiliates - Summarized Financial Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summarized Operating Data(a):
Undistributed earnings of foreign subsidiaries	$ 45,000,000	$ 4,000,000
SAIC-GMAC [Member]
Summarized Balance Sheet Data(a):
Finance receivables, net	13,459,000,000	10,408,000,000
Total assets	16,198,000,000	11,089,000,000
Debt	9,349,000,000	6,681,000,000
Total liabilities	13,807,000,000	9,330,000,000
Summarized Operating Data(a):
Finance charge income	1,053,000,000	940,000,000	$ 971,000,000
Provision for loan losses	(6,000,000)	18,000,000	45,000,000
Interest expense	337,000,000	257,000,000	338,000,000
Income before income taxes	661,000,000	570,000,000	463,000,000
Net income	$ 496,000,000	$ 428,000,000	$ 347,000,000
Ownership percentage	35.00%	35.00%	35.00%
Cash dividends received	$ 0	$ 129,000,000	$ 0
Undistributed earnings of foreign subsidiaries	$ 315,000,000	$ 142,000,000