Segment Reporting and Geographic Information - Operations Reporting by Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Total revenue	$ 1,878	$ 1,707	$ 1,515	$ 1,354	$ 1,305	$ 1,261	$ 1,191	$ 1,097	$ 6,454	$ 4,854	$ 3,344
Operating expenses, including leased vehicle expenses									3,493	2,009	1,223
Provision for loan losses									624	604	475
Interest expense									1,616	1,426	721
Acquisition and integration expenses									0	0	42
Equity income									116	0	0
Income before income taxes	$ 167	$ 231	$ 225	$ 214	$ 120	$ 208	$ 265	$ 222	837	815	883
Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Total revenue									4,777	2,909	2,376
Operating expenses, including leased vehicle expenses									2,925	1,385	893
Provision for loan losses									466	472	393
Interest expense									833	459	360
Acquisition and integration expenses											0
Equity income									0
Income before income taxes									553	593	730
Operating Segments [Member] | International [Member]
Segment Reporting Information [Line Items]
Total revenue									1,677	1,945	968
Operating expenses, including leased vehicle expenses									568	624	330
Provision for loan losses									158	132	82
Interest expense									722	954	362
Acquisition and integration expenses											42
Equity income									116
Income before income taxes									345	235	152
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Total revenue									13	56	43
Operating expenses, including leased vehicle expenses									0	0	0
Provision for loan losses									0	0	0
Interest expense									74	69	42
Acquisition and integration expenses											0
Equity income									0
Income before income taxes									(61)	(13)	1
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenue									(13)	(56)	(43)
Operating expenses, including leased vehicle expenses									0	0	0
Provision for loan losses									0	0	0
Interest expense									(13)	(56)	(43)
Acquisition and integration expenses											0
Equity income									0
Income before income taxes									$ 0	$ 0	$ 0