Guarantor Condensed Consolidating Financial Statements - Guarantor Income Statements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenue
Finance charge income	$ 812	$ 698	$ 1,564	$ 1,389
Leased vehicle income	2,107	1,383	4,038	2,562
Other income	71	57	136	118
Total revenue	2,990	2,138	5,738	4,069
Costs and expenses
Salaries and benefits	198	175	397	341
Other operating expenses	135	121	266	228
Total operating expenses	333	296	663	569
Leased vehicle expenses	1,549	1,062	2,978	1,951
Provision for loan losses	158	144	369	334
Interest expense	635	460	1,231	882
Total costs and expenses	2,675	1,962	5,241	3,736
Equity income	41	37	88	73
Income from continuing operations before income taxes	356	213	585	406
Income tax (benefit) provision	86	70	136	125
Income from continuing operations	270	143	449	281
(Loss) income from discontinued operations, net of tax (Note 2)	(208)	46	(185)	72
Net income	62	189	264	353
Comprehensive income	158	103	450	419
Eliminations [Member]
Revenue
Finance charge income	0	0	0	0
Leased vehicle income	0	0	0	0
Other income	(214)	(163)	(413)	(309)
Total revenue	(214)	(163)	(413)	(309)
Costs and expenses
Salaries and benefits	0	0	0	0
Other operating expenses	(119)	(98)	(229)	(191)
Total operating expenses	(119)	(98)	(229)	(191)
Leased vehicle expenses	0	0	0	0
Provision for loan losses	0	0	0	0
Interest expense	(95)	(65)	(184)	(118)
Total costs and expenses	(214)	(163)	(413)	(309)
Equity income	(551)	(504)	(1,081)	(927)
Income from continuing operations before income taxes	(551)	(504)	(1,081)	(927)
Income tax (benefit) provision	0	0	0	0
Income from continuing operations	(551)	(504)	(1,081)	(927)
(Loss) income from discontinued operations, net of tax (Note 2)	0	0	0	0
Net income	(551)	(504)	(1,081)	(927)
Comprehensive income	(681)	(416)	(1,315)	(1,037)
Parent Company [Member]
Revenue
Finance charge income	0	0	0	0
Leased vehicle income	0	0	0	0
Other income	0	0	0	(1)
Total revenue	0	0	0	(1)
Costs and expenses
Salaries and benefits	0	0	0	0
Other operating expenses	99	0	106	(4)
Total operating expenses	99	0	106	(4)
Leased vehicle expenses	0	0	0	0
Provision for loan losses	0	0	0	0
Interest expense	347	265	582	441
Total costs and expenses	446	265	688	437
Equity income	275	336	590	591
Income from continuing operations before income taxes	(171)	71	(98)	153
Income tax (benefit) provision	(233)	(118)	(362)	(200)
Income from continuing operations	62	189	264	353
(Loss) income from discontinued operations, net of tax (Note 2)	0	0	0	0
Net income	62	189	264	353
Comprehensive income	158	103	450	419
Guarantor [Member]
Revenue
Finance charge income	134	118	229	217
Leased vehicle income	0	0	0	0
Other income	291	210	564	415
Total revenue	425	328	793	632
Costs and expenses
Salaries and benefits	159	140	322	275
Other operating expenses	(39)	53	5	121
Total operating expenses	120	193	327	396
Leased vehicle expenses	0	0	0	0
Provision for loan losses	87	77	160	180
Interest expense	(62)	(91)	(29)	(121)
Total costs and expenses	145	179	458	455
Equity income	276	168	491	336
Income from continuing operations before income taxes	556	317	826	513
Income tax (benefit) provision	133	68	159	80
Income from continuing operations	423	249	667	433
(Loss) income from discontinued operations, net of tax (Note 2)	(7)	0	(7)	0
Net income	416	249	660	433
Comprehensive income	436	247	684	470
Non-Guarantors [Member]
Revenue
Finance charge income	678	580	1,335	1,172
Leased vehicle income	2,107	1,383	4,038	2,562
Other income	(6)	10	(15)	13
Total revenue	2,779	1,973	5,358	3,747
Costs and expenses
Salaries and benefits	39	35	75	66
Other operating expenses	194	166	384	302
Total operating expenses	233	201	459	368
Leased vehicle expenses	1,549	1,062	2,978	1,951
Provision for loan losses	71	67	209	154
Interest expense	445	351	862	680
Total costs and expenses	2,298	1,681	4,508	3,153
Equity income	41	37	88	73
Income from continuing operations before income taxes	522	329	938	667
Income tax (benefit) provision	186	120	339	245
Income from continuing operations	336	209	599	422
(Loss) income from discontinued operations, net of tax (Note 2)	(201)	46	(178)	72
Net income	135	255	421	494
Comprehensive income	$ 245	$ 169	$ 631	$ 567