Guarantor Consolidating Financial Statements - Guarantor Income Statements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Condensed Income Statements, Captions [Line Items]
Finance charge income									$ 3,475	$ 2,563		$ 1,594
Leased vehicle income									1,090	595		289
Other income									289	186		77
Total revenue	1,305	1,261	1,191	1,097	1,101	867	836	540	4,854	3,344		1,960
Salaries and benefits									614	448		298
Other operating expenses									548	322		100
Total operating expenses									1,162	770		398
Leased vehicle expenses									847	453		211
Provision for loan losses									604	475		304
Interest expense									1,426	721		283
Acquisition and integration expenses									0	42		20
Total costs and expenses									4,039	2,461		1,216
Income before income taxes	120	208	265	222	210	239	264	170	815	883		744
Income tax (benefit) provision									278	317		281
(Loss) income before equity in income of affiliates									537	566		463
Income (Loss) from Subsidiaries, Net of Tax									0	0	[1]	0	[1]
Net income	59	158	175	145	121	161	178	106	537	566		463
Comprehensive income									93	580		467
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Finance charge income									0	0		0
Leased vehicle income									0	0		0
Other income									68	56		45
Total revenue									68	56		45
Salaries and benefits									0	0		0
Other operating expenses									159	(100)		15
Total operating expenses									159	(100)		15
Leased vehicle expenses									0	0		0
Provision for loan losses									0	0		0
Interest expense									232	180		67
Acquisition and integration expenses										0		0
Total costs and expenses									391	80		82
Income before income taxes									(323)	(24)		(37)
Income tax (benefit) provision									(103)	(6)		(11)
(Loss) income before equity in income of affiliates									(220)	(18)		(26)
Income (Loss) from Subsidiaries, Net of Tax									757	584	[1]	489	[1]
Net income									537	566		463
Comprehensive income									93	580		467
Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Finance charge income									194	140		150
Leased vehicle income									0	0		0
Other income									432	433		194
Total revenue									626	573		344
Salaries and benefits									249	216		201
Other operating expenses									(17)	228		(115)
Total operating expenses									232	444		86
Leased vehicle expenses									0	0		0
Provision for loan losses									334	239		231
Interest expense									23	37		166
Acquisition and integration expenses										0		0
Total costs and expenses									589	720		483
Income before income taxes									37	(147)		(139)
Income tax (benefit) provision									12	(42)		(41)
(Loss) income before equity in income of affiliates									25	(105)		(98)
Income (Loss) from Subsidiaries, Net of Tax									523	551	[1]	599	[1]
Net income									548	446		501
Comprehensive income									491	449		501
Non-Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Finance charge income									3,281	2,423		1,444
Leased vehicle income									1,090	595		289
Other income									178	105		250
Total revenue									4,549	3,123		1,983
Salaries and benefits									365	232		97
Other operating expenses									657	441		200
Total operating expenses									1,022	673		297
Leased vehicle expenses									847	453		211
Provision for loan losses									270	236		73
Interest expense									1,309	665		462
Acquisition and integration expenses										42		20
Total costs and expenses									3,448	2,069		1,063
Income before income taxes									1,101	1,054		920
Income tax (benefit) provision									369	365		333
(Loss) income before equity in income of affiliates									732	689		587
Income (Loss) from Subsidiaries, Net of Tax									0	0	[1]	0	[1]
Net income									732	689		587
Comprehensive income									298	700		593
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Finance charge income									0	0		0
Leased vehicle income									0	0		0
Other income									(389)	(408)		(412)
Total revenue									(389)	(408)		(412)
Salaries and benefits									0	0		0
Other operating expenses									(251)	(247)		0
Total operating expenses									(251)	(247)		0
Leased vehicle expenses									0	0		0
Provision for loan losses									0	0		0
Interest expense									(138)	(161)		(412)
Acquisition and integration expenses										0		0
Total costs and expenses									(389)	(408)		(412)
Income before income taxes									0	0		0
Income tax (benefit) provision									0	0		0
(Loss) income before equity in income of affiliates									0	0		0
Income (Loss) from Subsidiaries, Net of Tax									(1,280)	(1,135)	[1]	(1,088)	[1]
Net income									(1,280)	(1,135)		(1,088)
Comprehensive income									$ (789)	$ (1,149)		$ (1,094)

[1] Equity in income of affiliates has been reclassified from revenue to present the amount after the income tax provision.