Equity in Net Assets of Non-consolidated Affiliate (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Noncontrolling Interest [Line Items]
Net income	$ 41,000,000	$ 37,000,000	$ 88,000,000	$ 73,000,000
SAIC-GMAC [Member]
Noncontrolling Interest [Line Items]
Finance charge income	256,000,000	234,000,000	514,000,000	471,000,000
Provision for loan losses	4,000,000	6,000,000	(11,000,000)	14,000,000
Interest expense	82,000,000	63,000,000	158,000,000	127,000,000
Income before income taxes	155,000,000	140,000,000	333,000,000	274,000,000
Net income	$ 116,000,000	$ 105,000,000	$ 250,000,000	205,000,000
Ownership interest (percent)	35.00%		35.00%
Cash dividends received			$ 0	$ 129,000,000
Undistributed earnings	$ 230,000,000		$ 230,000,000		$ 142,000,000