Segment Reporting and Geographic Information - Operations Reporting by Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total revenue	$ 3,599	$ 3,518	$ 3,488	$ 3,411	$ 3,252	$ 3,161	$ 2,990	$ 2,748	$ 14,016	$ 12,151	$ 8,983
Operating expenses									1,522	1,390	1,250
Leased vehicle expenses									6,917	6,415	4,506
Provision for loan losses (Note 3)									642	757	644
Interest expense									3,225	2,566	1,972
Equity income									183	173	151
Income from continuing operations before income taxes	$ 416	$ 498	$ 536	$ 443	$ 450	$ 186	$ 270	$ 179	1,893	1,196	762
Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Total revenue									12,771	10,999	7,948
Operating expenses									1,125	1,050	891
Leased vehicle expenses									6,879	6,391	4,499
Provision for loan losses (Note 3)									490	623	566
Interest expense									2,735	2,032	1,481
Equity income									0	0	0
Income from continuing operations before income taxes									1,542	903	511
Operating Segments [Member] | International [Member]
Segment Reporting Information [Line Items]
Total revenue									1,245	1,152	1,035
Operating expenses									397	340	359
Leased vehicle expenses									38	24	7
Provision for loan losses (Note 3)									152	134	78
Interest expense									490	534	491
Equity income									183	173	151
Income from continuing operations before income taxes									$ 351	$ 293	$ 251