Guarantor Condensed Consolidating Financial Statements - Guarantor Income Statements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue
Finance charge income	$ 866	$ 752
Leased vehicle income	2,447	1,931
Other income	98	65
Total revenue	3,411	2,748
Costs and expenses
Salaries and benefits	221	199
Other operating expenses	144	131
Total operating expenses	365	330
Leased vehicle expenses	1,787	1,429
Provision for loan losses (Note 3)	136	211
Interest expense	732	596
Total costs and expenses	3,020	2,566
Equity income	52	47
Income from continuing operations before income taxes	443	229
Income tax (benefit) provision	74	50
Income from continuing operations	369	179
Income from discontinued operations, net of tax		23
Net income	369	202
Net income attributable to common shareholder	355	202
Comprehensive income	429	292
Eliminations [Member]
Revenue
Finance charge income	0	0
Leased vehicle income	0	0
Other income	(243)	(199)
Total revenue	(243)	(199)
Costs and expenses
Salaries and benefits	0	0
Other operating expenses	(138)	(110)
Total operating expenses	(138)	(110)
Leased vehicle expenses	0	0
Provision for loan losses (Note 3)	0	0
Interest expense	(105)	(89)
Total costs and expenses	(243)	(199)
Equity income	(917)	(530)
Income from continuing operations before income taxes	(917)	(530)
Income tax (benefit) provision	0	0
Income from continuing operations		(530)
Income from discontinued operations, net of tax		0
Net income	(917)	(530)
Net income attributable to common shareholder	(917)
Comprehensive income	(946)	(634)
Parent Company [Member]
Revenue
Finance charge income	0	0
Leased vehicle income	0	0
Other income	2	0
Total revenue	2	0
Costs and expenses
Salaries and benefits	0	0
Other operating expenses	82	7
Total operating expenses	82	7
Leased vehicle expenses	0	0
Provision for loan losses (Note 3)	0	0
Interest expense	101	235
Total costs and expenses	183	242
Equity income	475	315
Income from continuing operations before income taxes	294	73
Income tax (benefit) provision	(75)	(129)
Income from continuing operations		202
Income from discontinued operations, net of tax		0
Net income	369	202
Net income attributable to common shareholder	355
Comprehensive income	429	292
Guarantor [Member]
Revenue
Finance charge income	169	95
Leased vehicle income	0	0
Other income	311	273
Total revenue	480	368
Costs and expenses
Salaries and benefits	181	163
Other operating expenses	(16)	44
Total operating expenses	165	207
Leased vehicle expenses	0	0
Provision for loan losses (Note 3)	88	73
Interest expense	290	33
Total costs and expenses	543	313
Equity income	442	215
Income from continuing operations before income taxes	379	270
Income tax (benefit) provision	(23)	26
Income from continuing operations		244
Income from discontinued operations, net of tax		0
Net income	402	244
Net income attributable to common shareholder	402
Comprehensive income	378	248
Non-Guarantors [Member]
Revenue
Finance charge income	697	657
Leased vehicle income	2,447	1,931
Other income	28	(9)
Total revenue	3,172	2,579
Costs and expenses
Salaries and benefits	40	36
Other operating expenses	216	190
Total operating expenses	256	226
Leased vehicle expenses	1,787	1,429
Provision for loan losses (Note 3)	48	138
Interest expense	446	417
Total costs and expenses	2,537	2,210
Equity income	52	47
Income from continuing operations before income taxes	687	416
Income tax (benefit) provision	172	153
Income from continuing operations		263
Income from discontinued operations, net of tax		23
Net income	515	286
Net income attributable to common shareholder	515
Comprehensive income	$ 568	$ 386