Consolidating Condensed Statements of Operations (Detail) - 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	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Revenues	$ 2,050	$ 2,778	$ 2,328	$ 1,968	$ 2,019	$ 2,752	$ 2,238	$ 1,839	$ 9,124	$ 8,848	$ 8,659
Operating									4,639	4,472	4,382
Vehicle depreciation and lease charges, net									2,179	2,221	2,047
Selling, general and administrative									1,220	1,120	1,134
Vehicle interest, net									314	286	284
Non-vehicle related depreciation and amortization									256	259	253
Interest expense									188	188	203
Intercompany interest expense (income)									0	0	0
Early extinguishment of debt									19	3	27
Restructuring Charges									22	63	29
Transaction-related costs, net									20	23	21
Impairment of Intangible Assets (Excluding Goodwill)										2
Total expenses									8,857	8,637	8,380
Income before income taxes									267	211	279
Provision for (benefit from) income taxes									102	(150)	116
Equity in earnings (loss) of subsidiaries									0	0	0
Net income									165	361	163
Total comprehensive income									62	491	156
Payments for (Proceeds from) Other Investing Activities									(44)	5	1
Net Cash Provided by (Used in) Investing Activities									(3,426)	(2,204)	(2,182)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash									(16)	45	(6)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect									(166)	181	3
Program cash	115				283				115	283
Restricted Cash	5				7				5	7
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	735				901				735	901	720	$ 717
Parent Company
Condensed Financial Statements, Captions [Line Items]
Revenues									0	0	0
Operating									4	3	4
Vehicle depreciation and lease charges, net									0	0	0
Selling, general and administrative									48	39	38
Vehicle interest, net									0	0	0
Non-vehicle related depreciation and amortization									0	0	0
Interest expense									0	0	0
Intercompany interest expense (income)									(12)	(12)	(13)
Early extinguishment of debt									0	0	0
Restructuring Charges									0	0	0
Transaction-related costs, net									0	0	0
Impairment of Intangible Assets (Excluding Goodwill)										0
Total expenses									40	30	29
Income before income taxes									(40)	(30)	(29)
Provision for (benefit from) income taxes									(10)	(5)	(11)
Equity in earnings (loss) of subsidiaries									195	386	181
Net income									165	361	163
Total comprehensive income									62	491	156
Payments for (Proceeds from) Other Investing Activities									0	100	118
Net Cash Provided by (Used in) Investing Activities									0	100	118
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash									0	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect									(3)	1	(1)
Program cash	0				0				0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1				4				1	4	3	4
Subsidiary Issuers
Condensed Financial Statements, Captions [Line Items]
Revenues									0	0	0
Operating									7	20	18
Vehicle depreciation and lease charges, net									0	0	0
Selling, general and administrative									11	8	18
Vehicle interest, net									0	0	0
Non-vehicle related depreciation and amortization									1	1	2
Interest expense									153	157	141
Intercompany interest expense (income)									(11)	95	(7)
Early extinguishment of debt									19	4	10
Restructuring Charges									0	7	0
Transaction-related costs, net									1	1	2
Impairment of Intangible Assets (Excluding Goodwill)										0
Total expenses									181	293	184
Income before income taxes									(181)	(293)	(184)
Provision for (benefit from) income taxes									(48)	267	(70)
Equity in earnings (loss) of subsidiaries									328	946	295
Net income									195	386	181
Total comprehensive income									92	515	173
Payments for (Proceeds from) Other Investing Activities									(8)	110	(1)
Net Cash Provided by (Used in) Investing Activities									(33)	106	(4)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash									0	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect									(2)	2	(58)
Program cash	0				0				0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	12				14				12	14	12	70
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Revenues									5,431	5,312	5,343
Operating									2,668	2,598	2,622
Vehicle depreciation and lease charges, net									2,162	2,226	1,993
Selling, general and administrative									662	619	631
Vehicle interest, net									229	199	198
Non-vehicle related depreciation and amortization									145	160	155
Interest expense									3	1	3
Intercompany interest expense (income)									26	23	23
Early extinguishment of debt									0	0	0
Restructuring Charges									11	44	9
Transaction-related costs, net									4	3	1
Impairment of Intangible Assets (Excluding Goodwill)										2
Total expenses									5,910	5,875	5,635
Income before income taxes									(479)	(563)	(292)
Provision for (benefit from) income taxes									93	(527)	123
Equity in earnings (loss) of subsidiaries									900	982	710
Net income									328	946	295
Total comprehensive income									228	1,073	283
Payments for (Proceeds from) Other Investing Activities									0	110	0
Net Cash Provided by (Used in) Investing Activities									(95)	24	(65)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash									0	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect									1	0	0
Program cash	0				0				0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1				0				1	0	0	0
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Revenues									6,006	5,931	5,510
Operating									1,960	1,851	1,738
Vehicle depreciation and lease charges, net									2,102	2,183	2,045
Selling, general and administrative									499	454	447
Vehicle interest, net									313	294	289
Non-vehicle related depreciation and amortization									110	98	96
Interest expense									32	30	59
Intercompany interest expense (income)									(3)	(106)	(3)
Early extinguishment of debt									0	(1)	17
Restructuring Charges									11	12	20
Transaction-related costs, net									15	19	18
Impairment of Intangible Assets (Excluding Goodwill)										0
Total expenses									5,039	4,834	4,726
Income before income taxes									967	1,097	784
Provision for (benefit from) income taxes									67	115	74
Equity in earnings (loss) of subsidiaries									0	0	0
Net income									900	982	710
Total comprehensive income									806	1,103	712
Payments for (Proceeds from) Other Investing Activities									(36)	5	2
Net Cash Provided by (Used in) Investing Activities									(3,702)	(2,378)	(2,401)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash									(16)	45	(6)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect									(162)	178	62
Program cash	115				283				115	283
Restricted Cash	5				7				5	7
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	721				883				721	883	705	643
Eliminations
Condensed Financial Statements, Captions [Line Items]
Revenues									(2,313)	(2,395)	(2,194)
Operating									0	0	0
Vehicle depreciation and lease charges, net									(2,085)	(2,188)	(1,991)
Selling, general and administrative									0	0	0
Vehicle interest, net									(228)	(207)	(203)
Non-vehicle related depreciation and amortization									0	0	0
Interest expense									0	0	0
Intercompany interest expense (income)									0	0	0
Early extinguishment of debt									0	0	0
Restructuring Charges									0	0	0
Transaction-related costs, net									0	0	0
Impairment of Intangible Assets (Excluding Goodwill)										0
Total expenses									(2,313)	(2,395)	(2,194)
Income before income taxes									0	0	0
Provision for (benefit from) income taxes									0	0	0
Equity in earnings (loss) of subsidiaries									(1,423)	(2,314)	(1,186)
Net income									(1,423)	(2,314)	(1,186)
Total comprehensive income									(1,126)	(2,691)	(1,168)
Payments for (Proceeds from) Other Investing Activities									0	(320)	(118)
Net Cash Provided by (Used in) Investing Activities									404	(56)	170
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash									0	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect									0	0	0
Program cash	0				0				0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 0				$ 0				$ 0	$ 0	$ 0	$ 0