Consolidating Condensed Statements of Operations (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Revenues	$ 2,162	$ 2,753	$ 2,337	$ 1,920	$ 2,050	$ 2,778	$ 2,328	$ 1,968	$ 9,172	$ 9,124	$ 8,848
Operating									4,698	4,639	4,472
Vehicle depreciation and lease charges, net									2,063	2,179	2,221
Selling, general and administrative									1,237	1,220	1,120
Vehicle interest, net									344	314	286
Non-vehicle related depreciation and amortization									263	256	259
Interest expense									178	188	188
Intercompany interest expense (income)									0	0	0
Early extinguishment of debt									12	19	3
Restructuring Charges									80	22	63
Transaction-related costs, net									10	20	23
Impairment of Intangible Assets (Excluding Goodwill)											2
Total expenses									8,885	8,857	8,637
Income before income taxes									287	267	211
Provision for (benefit from) income taxes									(15)	102	(150)
Equity in earnings (loss) of subsidiaries									0	0	0
Net income	$ 142	$ 189	$ 62	$ (91)	$ 13	$ 213	$ 26	$ (87)	302	165	361
Total comprehensive income									277	62	491
Payments for (Proceeds from) Other Investing Activities									81	(44)	5
Net Cash Provided by (Used in) Investing Activities									(2,752)	(3,426)	(2,204)
Parent Company
Condensed Financial Statements, Captions [Line Items]
Revenues									0	0	0
Operating									2	4	3
Vehicle depreciation and lease charges, net									0	0	0
Selling, general and administrative									50	48	39
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)	(12)
Early extinguishment of debt									0	0	0
Restructuring Charges									18	0	0
Transaction-related costs, net									0	0	0
Impairment of Intangible Assets (Excluding Goodwill)											0
Total expenses									58	40	30
Income before income taxes									(58)	(40)	(30)
Provision for (benefit from) income taxes									(12)	(10)	(5)
Equity in earnings (loss) of subsidiaries									348	195	386
Net income									302	165	361
Total comprehensive income									277	62	491
Payments for (Proceeds from) Other Investing Activities									0	0	100
Net Cash Provided by (Used in) Investing Activities									0	0	100
Subsidiary Issuers
Condensed Financial Statements, Captions [Line Items]
Revenues									0	0	0
Operating									0	7	20
Vehicle depreciation and lease charges, net									0	0	0
Selling, general and administrative									17	11	8
Vehicle interest, net									3	0	0
Non-vehicle related depreciation and amortization									10	1	1
Interest expense									131	153	157
Intercompany interest expense (income)									10	(11)	95
Early extinguishment of debt									12	19	4
Restructuring Charges									0	0	7
Transaction-related costs, net									4	1	1
Impairment of Intangible Assets (Excluding Goodwill)											0
Total expenses									187	181	293
Income before income taxes									(187)	(181)	(293)
Provision for (benefit from) income taxes									(220)	(48)	267
Equity in earnings (loss) of subsidiaries									315	328	946
Net income									348	195	386
Total comprehensive income									323	92	515
Payments for (Proceeds from) Other Investing Activities									(75)	(8)	110
Net Cash Provided by (Used in) Investing Activities									(224)	(33)	106
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Revenues									5,613	5,431	5,312
Operating									2,788	2,668	2,598
Vehicle depreciation and lease charges, net									2,188	2,162	2,226
Selling, general and administrative									700	662	619
Vehicle interest, net									269	229	199
Non-vehicle related depreciation and amortization									153	145	160
Interest expense									2	3	1
Intercompany interest expense (income)									59	26	23
Early extinguishment of debt									0	0	0
Restructuring Charges									38	11	44
Transaction-related costs, net									(6)	4	3
Impairment of Intangible Assets (Excluding Goodwill)											2
Total expenses									6,191	5,910	5,875
Income before income taxes									(578)	(479)	(563)
Provision for (benefit from) income taxes									(24)	93	(527)
Equity in earnings (loss) of subsidiaries									869	900	982
Net income									315	328	946
Total comprehensive income									312	228	1,073
Payments for (Proceeds from) Other Investing Activities									12	0	110
Net Cash Provided by (Used in) Investing Activities									(134)	(95)	24
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Revenues									5,923	6,006	5,931
Operating									1,908	1,960	1,851
Vehicle depreciation and lease charges, net									1,969	2,102	2,183
Selling, general and administrative									470	499	454
Vehicle interest, net									342	313	294
Non-vehicle related depreciation and amortization									100	110	98
Interest expense									45	32	30
Intercompany interest expense (income)									(57)	(3)	(106)
Early extinguishment of debt									0	0	(1)
Restructuring Charges									24	11	12
Transaction-related costs, net									12	15	19
Impairment of Intangible Assets (Excluding Goodwill)											0
Total expenses									4,813	5,039	4,834
Income before income taxes									1,110	967	1,097
Provision for (benefit from) income taxes									241	67	115
Equity in earnings (loss) of subsidiaries									0	0	0
Net income									869	900	982
Total comprehensive income									860	806	1,103
Payments for (Proceeds from) Other Investing Activities									69	(36)	5
Net Cash Provided by (Used in) Investing Activities									(2,469)	(3,702)	(2,378)
Eliminations
Condensed Financial Statements, Captions [Line Items]
Revenues									(2,364)	(2,313)	(2,395)
Operating									0	0	0
Vehicle depreciation and lease charges, net									(2,094)	(2,085)	(2,188)
Selling, general and administrative									0	0	0
Vehicle interest, net									(270)	(228)	(207)
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									(2,364)	(2,313)	(2,395)
Income before income taxes									0	0	0
Provision for (benefit from) income taxes									0	0	0
Equity in earnings (loss) of subsidiaries									(1,532)	(1,423)	(2,314)
Net income									(1,532)	(1,423)	(2,314)
Total comprehensive income									(1,495)	(1,126)	(2,691)
Payments for (Proceeds from) Other Investing Activities									75	0	(320)
Net Cash Provided by (Used in) Investing Activities									$ 75	$ 404	$ (56)