Segment Reporting - Operations Reporting by Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Total revenue	$ 3,518	$ 3,161	$ 10,417	$ 8,899
Operating expenses	369	346	1,116	1,009
Leased vehicle expenses	1,677	1,670	5,148	4,648
Provision for loan losses	180	204	444	573
Interest expense	838	672	2,373	1,903
Equity income	44	41	141	129
Income from continuing operations before income taxes	498	310	1,477	895
Operating Segments [Member] | North America Segment [Member]
Segment Reporting Information [Line Items]
Total revenue	3,217	2,868	9,482	8,042
Operating expenses	273	265	820	766
Leased vehicle expenses	1,668	1,662	5,121	4,631
Provision for loan losses	146	177	333	497
Interest expense	715	536	1,997	1,488
Equity income	0	0	0	0
Income from continuing operations before income taxes	415	228	1,211	660
Operating Segments [Member] | International Segment [Member]
Segment Reporting Information [Line Items]
Total revenue	301	293	935	857
Operating expenses	96	81	296	243
Leased vehicle expenses	9	8	27	17
Provision for loan losses	34	27	111	76
Interest expense	123	136	376	415
Equity income	44	41	141	129
Income from continuing operations before income taxes	$ 83	$ 82	$ 266	$ 235