Consolidating Condensed Statements of Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 900	$ 735	$ 901	$ 720
Net cash provided by (used in) operating activities	2,586	2,609	2,648
Investing activities
Property and equipment additions	(250)	(231)	(197)
Proceeds received on asset sales	11	17	8
Net assets acquired (net of cash acquired)	(77)	(91)	(21)
intercompany loan receipts		0	0
Other, net	81	(44)	5
Net cash used in investing activities exclusive of vehicle programs	(235)	(349)	(205)
Vehicle programs:
Investment In Vehicles	(12,887)	(12,589)	(11,538)
Proceeds received on disposition of vehicles	10,460	9,648	9,600
Repayments of Related Party Debt	(251)	(188)	(61)
Proceeds from Related Party Debt	161	52	0
Net Cash Used In Investing Activities Of Vehicle Programs	2,517	3,077	1,999
Net Cash Provided by (Used in) Investing Activities	(2,752)	(3,426)	(2,204)
Financing activities
Proceeds from borrowings	402	485	589
Principal payments on borrowings	(509)	(515)	(602)
Proceeds from (Repayments of) Short-term Debt	(1)	(4)	(4)
Debt financing fees	(7)	(15)	(9)
Payments for Repurchase of Common Stock	(67)	(216)	(210)
Intercompany loan borrowings		0	0
Other, net	0	3	1
Net cash used in financing activities exclusive of vehicle programs	(182)	(262)	(235)
Vehicle programs:
Proceeds from borrowings	19,869	17,339	17,212
Principal payments on borrowings	(19,346)	(16,385)	(17,269)
Debt financing fees	(23)	(25)	(16)
Net cash provided by financing activities of vehicle programs	500	929	(73)
Net cash provided by (used in) financing activities	318	667	(308)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	13	(16)	45
Net increase (decrease) in cash and cash equivalents, program and restricted cash	165	(166)	181
Parent Company
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1	1	4	3
Net cash provided by (used in) operating activities	67	210	110
Investing activities
Property and equipment additions	0	0	0
Proceeds received on asset sales	0	0	0
Net assets acquired (net of cash acquired)	0	0	0
intercompany loan receipts		0	0
Other, net	0	0	100
Net cash used in investing activities exclusive of vehicle programs	0	0	100
Vehicle programs:
Investment In Vehicles	0	0	0
Proceeds received on disposition of vehicles	0	0	0
Repayments of Related Party Debt	0	0	0
Proceeds from Related Party Debt	0	0
Net Cash Used In Investing Activities Of Vehicle Programs	0	0	0
Net Cash Provided by (Used in) Investing Activities	0	0	100
Financing activities
Proceeds from borrowings	0	0	0
Principal payments on borrowings	0	0	0
Proceeds from (Repayments of) Short-term Debt	0	0	0
Debt financing fees	0	0	0
Payments for Repurchase of Common Stock	(67)	(216)	(210)
Intercompany loan borrowings		0	0
Other, net	0	3	1
Net cash used in financing activities exclusive of vehicle programs	(67)	(213)	(209)
Vehicle programs:
Proceeds from borrowings	0	0	0
Principal payments on borrowings	0	0	0
Debt financing fees	0	0	0
Net cash provided by financing activities of vehicle programs	0	0	0
Net cash provided by (used in) financing activities	(67)	(213)	(209)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents, program and restricted cash	0	(3)	1
Subsidiary Issuers
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	12	12	14	12
Net cash provided by (used in) operating activities	293	235	(89)
Investing activities
Property and equipment additions	(79)	(64)	(49)
Proceeds received on asset sales	1	2	1
Net assets acquired (net of cash acquired)	(1)	(3)	(1)
intercompany loan receipts		0	0
Other, net	(75)	(8)	110
Net cash used in investing activities exclusive of vehicle programs	(154)	(73)	61
Vehicle programs:
Investment In Vehicles	(118)	(2)	(1)
Proceeds received on disposition of vehicles	48	42	46
Repayments of Related Party Debt	0	0	0
Proceeds from Related Party Debt	0	0
Net Cash Used In Investing Activities Of Vehicle Programs	70	(40)	(45)
Net Cash Provided by (Used in) Investing Activities	(224)	(33)	106
Financing activities
Proceeds from borrowings	400	81	325
Principal payments on borrowings	(502)	(510)	(406)
Proceeds from (Repayments of) Short-term Debt	0	0	0
Debt financing fees	(7)	(9)	(5)
Payments for Repurchase of Common Stock	0	0	0
Intercompany loan borrowings		404	264
Other, net	(61)	(167)	(192)
Net cash used in financing activities exclusive of vehicle programs	(170)	(201)	(14)
Vehicle programs:
Proceeds from borrowings	114	0	0
Principal payments on borrowings	(13)	(3)	(1)
Debt financing fees	0	0	0
Net cash provided by financing activities of vehicle programs	101	(3)	(1)
Net cash provided by (used in) financing activities	(69)	(204)	(15)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents, program and restricted cash	0	(2)	2
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	1	0	0
Net cash provided by (used in) operating activities	246	193	97
Investing activities
Property and equipment additions	(100)	(88)	(81)
Proceeds received on asset sales	0	4	0
Net assets acquired (net of cash acquired)	(24)	(10)	(5)
intercompany loan receipts		0	0
Other, net	12	0	110
Net cash used in investing activities exclusive of vehicle programs	(112)	(94)	24
Vehicle programs:
Investment In Vehicles	(22)	(1)	0
Proceeds received on disposition of vehicles	0	0	0
Repayments of Related Party Debt	0	0	0
Proceeds from Related Party Debt	0	0
Net Cash Used In Investing Activities Of Vehicle Programs	22	1	0
Net Cash Provided by (Used in) Investing Activities	(134)	(95)	24
Financing activities
Proceeds from borrowings	0	0	0
Principal payments on borrowings	(3)	(3)	(2)
Proceeds from (Repayments of) Short-term Debt	0	0	0
Debt financing fees	0	0	0
Payments for Repurchase of Common Stock	0	0	0
Intercompany loan borrowings		0	0
Other, net	(98)	(85)	(110)
Net cash used in financing activities exclusive of vehicle programs	(101)	(88)	(112)
Vehicle programs:
Proceeds from borrowings	0	0	0
Principal payments on borrowings	(12)	(9)	(9)
Debt financing fees	0	0	0
Net cash provided by financing activities of vehicle programs	(12)	(9)	(9)
Net cash provided by (used in) financing activities	(113)	(97)	(121)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents, program and restricted cash	(1)	1	0
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	887	721	883	705
Net cash provided by (used in) operating activities	2,394	2,380	2,697
Investing activities
Property and equipment additions	(71)	(79)	(67)
Proceeds received on asset sales	10	11	7
Net assets acquired (net of cash acquired)	(52)	(78)	(15)
intercompany loan receipts		(404)	(264)
Other, net	69	(36)	5
Net cash used in investing activities exclusive of vehicle programs	(44)	(586)	(334)
Vehicle programs:
Investment In Vehicles	(12,747)	(12,586)	(11,537)
Proceeds received on disposition of vehicles	10,412	9,606	9,554
Repayments of Related Party Debt	(251)	(188)	(61)
Proceeds from Related Party Debt	161	52
Net Cash Used In Investing Activities Of Vehicle Programs	2,425	3,116	2,044
Net Cash Provided by (Used in) Investing Activities	(2,469)	(3,702)	(2,378)
Financing activities
Proceeds from borrowings	2	404	264
Principal payments on borrowings	(4)	(2)	(194)
Proceeds from (Repayments of) Short-term Debt	(1)	(4)	(4)
Debt financing fees	0	(6)	(4)
Payments for Repurchase of Common Stock	0	0	0
Intercompany loan borrowings		0	0
Other, net	(180)	(157)	(185)
Net cash used in financing activities exclusive of vehicle programs	(183)	235	(123)
Vehicle programs:
Proceeds from borrowings	19,755	17,339	17,212
Principal payments on borrowings	(19,321)	(16,373)	(17,259)
Debt financing fees	(23)	(25)	(16)
Net cash provided by financing activities of vehicle programs	411	941	(63)
Net cash provided by (used in) financing activities	228	1,176	(186)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	13	(16)	45
Net increase (decrease) in cash and cash equivalents, program and restricted cash	166	(162)	178
Eliminations
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0	$ 0
Net cash provided by (used in) operating activities	(414)	(409)	(167)
Investing activities
Property and equipment additions	0	0	0
Proceeds received on asset sales	0	0	0
Net assets acquired (net of cash acquired)	0	0	0
intercompany loan receipts		404	264
Other, net	75	0	(320)
Net cash used in investing activities exclusive of vehicle programs	75	404	(56)
Vehicle programs:
Investment In Vehicles	0	0	0
Proceeds received on disposition of vehicles	0	0	0
Repayments of Related Party Debt	0	0	0
Proceeds from Related Party Debt	0	0
Net Cash Used In Investing Activities Of Vehicle Programs	0	0	0
Net Cash Provided by (Used in) Investing Activities	75	404	(56)
Financing activities
Proceeds from borrowings	0	0	0
Principal payments on borrowings	0	0	0
Proceeds from (Repayments of) Short-term Debt	0	0	0
Debt financing fees	0	0	0
Payments for Repurchase of Common Stock	0	0	0
Intercompany loan borrowings		(404)	(264)
Other, net	339	409	487
Net cash used in financing activities exclusive of vehicle programs	339	5	223
Vehicle programs:
Proceeds from borrowings	0	0	0
Principal payments on borrowings	0	0	0
Debt financing fees	0	0	0
Net cash provided by financing activities of vehicle programs	0	0	0
Net cash provided by (used in) financing activities	339	5	223
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents, program and restricted cash	$ 0	$ 0	$ 0