Segment Reporting - Operations Reporting by Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Total revenue	$ 3,488	$ 2,990	$ 6,899	$ 5,738
Operating expenses	382	333	747	663
Leased vehicle expenses	1,684	1,549	3,471	2,978
Provision for loan losses	128	158	264	369
Interest expense	803	635	1,535	1,231
Equity income	45	41	97	88
Income from continuing operations before income taxes	536	356	979	585
Operating Segments [Member] | North America Segment [Member]
Segment Reporting Information [Line Items]
Total revenue	3,180	2,700	6,265	5,174
Operating expenses	276	253	547	501
Leased vehicle expenses	1,675	1,543	3,453	2,969
Provision for loan losses	90	133	187	320
Interest expense	685	497	1,282	952
Equity income	0	0	0	0
Income from continuing operations before income taxes	454	274	796	432
Operating Segments [Member] | International Segment [Member]
Segment Reporting Information [Line Items]
Total revenue	308	290	634	564
Operating expenses	106	80	200	162
Leased vehicle expenses	9	6	18	9
Provision for loan losses	38	25	77	49
Interest expense	118	138	253	279
Equity income	45	41	97	88
Income from continuing operations before income taxes	$ 82	$ 82	$ 183	$ 153