Consolidating Condensed Statements of Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 735	$ 901	$ 720	$ 717
Net cash provided by (used in) operating activities	2,609	2,648	2,640
Investing activities
Property and equipment additions	(231)	(197)	(190)
Proceeds received on asset sales	17	8	19
Net assets acquired (net of cash acquired)	(91)	(21)	(55)
intercompany loan receipts	0	0	0
Other, net	(44)	5	1
Net cash used in investing activities exclusive of vehicle programs	(349)	(205)	(225)
Vehicle programs:
Investment In Vehicles	(12,589)	(11,538)	(12,461)
Proceeds received on disposition of vehicles	9,648	9,600	10,504
Repayments of Related Party Debt	(188)	(61)	0
Proceeds from Related Party Debt	52	0	0
Net Cash Used In Investing Activities Of Vehicle Programs	(3,077)	(1,999)	(1,957)
Net cash used in investing activities	(3,426)	(2,204)	(2,182)
Financing activities
Proceeds from borrowings	485	589	894
Principal payments on borrowings	(515)	(602)	(847)
Proceeds from (Repayments of) Short-term Debt	(4)	(4)	4
Debt financing fees	(15)	(9)	(20)
Payments for Repurchase of Common Stock	(216)	(210)	(398)
Intercompany loan borrowings	0	0	0
Other, net	3	1	0
Net cash used in financing activities exclusive of vehicle programs	(262)	(235)	(367)
Vehicle programs:
Proceeds from borrowings	17,339	17,212	15,769
Principal payments on borrowings	(16,385)	(17,269)	(15,826)
Debt financing fees	(25)	(16)	(25)
Net cash provided by financing activities of vehicle programs	929	(73)	(82)
Net cash provided by (used in) financing activities	667	(308)	(449)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	(16)	45	(6)
Net (decrease) increase in cash and cash equivalents, program and restricted cash	(166)	181	3
Parent Company
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1	4	3	4
Net cash provided by (used in) operating activities	210	110	279
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	0
Other, net	0	100	118
Net cash used in investing activities exclusive of vehicle programs	0	100	118
Vehicle programs:
Investment In Vehicles	0	0	0
Proceeds received on disposition of vehicles	0	0	0
Repayments of Related Party Debt	0	0
Proceeds from Related Party Debt	0
Net Cash Used In Investing Activities Of Vehicle Programs	0	0	0
Net cash used in investing activities	0	100	118
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	(216)	(210)	(398)
Intercompany loan borrowings	0	0	0
Other, net	3	1	0
Net cash used in financing activities exclusive of vehicle programs	(213)	(209)	(398)
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	(213)	(209)	(398)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	0	0	0
Net (decrease) increase in cash and cash equivalents, program and restricted cash	(3)	1	(1)
Subsidiary Issuers
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	12	14	12	70
Net cash provided by (used in) operating activities	235	(89)	(10)
Investing activities
Property and equipment additions	(64)	(49)	(32)
Proceeds received on asset sales	2	1	7
Net assets acquired (net of cash acquired)	(3)	(1)	0
intercompany loan receipts	0	0	0
Other, net	(8)	110	(1)
Net cash used in investing activities exclusive of vehicle programs	(73)	61	(26)
Vehicle programs:
Investment In Vehicles	(2)	(1)	(9)
Proceeds received on disposition of vehicles	42	46	31
Repayments of Related Party Debt	0	0
Proceeds from Related Party Debt	0
Net Cash Used In Investing Activities Of Vehicle Programs	40	45	22
Net cash used in investing activities	(33)	106	(4)
Financing activities
Proceeds from borrowings	81	325	557
Principal payments on borrowings	(510)	(406)	(525)
Proceeds from (Repayments of) Short-term Debt	0	0	0
Debt financing fees	(9)	(5)	(15)
Payments for Repurchase of Common Stock	0	0	0
Intercompany loan borrowings	404	264	316
Other, net	(167)	(192)	(385)
Net cash used in financing activities exclusive of vehicle programs	(201)	(14)	(52)
Vehicle programs:
Proceeds from borrowings	0	0	8
Principal payments on borrowings	(3)	(1)	0
Debt financing fees	0	0	0
Net cash provided by financing activities of vehicle programs	(3)	(1)	8
Net cash provided by (used in) financing activities	(204)	(15)	(44)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	0	0	0
Net (decrease) increase in cash and cash equivalents, program and restricted cash	(2)	2	(58)
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1	0	0	0
Net cash provided by (used in) operating activities	193	97	80
Investing activities
Property and equipment additions	(88)	(81)	(89)
Proceeds received on asset sales	4	0	4
Net assets acquired (net of cash acquired)	(10)	(5)	(4)
intercompany loan receipts	0	0	28
Other, net	0	110	0
Net cash used in investing activities exclusive of vehicle programs	(94)	24	(61)
Vehicle programs:
Investment In Vehicles	(1)	0	(4)
Proceeds received on disposition of vehicles	0	0	0
Repayments of Related Party Debt	0	0
Proceeds from Related Party Debt	0
Net Cash Used In Investing Activities Of Vehicle Programs	(1)	0	(4)
Net cash used in investing activities	(95)	24	(65)
Financing activities
Proceeds from borrowings	0	0	0
Principal payments on borrowings	(3)	(2)	(5)
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	0
Other, net	(85)	(110)	0
Net cash used in financing activities exclusive of vehicle programs	(88)	(112)	(5)
Vehicle programs:
Proceeds from borrowings	0	0	0
Principal payments on borrowings	(9)	(9)	(9)
Debt financing fees	0	0	(1)
Net cash provided by financing activities of vehicle programs	(9)	(9)	(10)
Net cash provided by (used in) financing activities	(97)	(121)	(15)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	0	0	0
Net (decrease) increase in cash and cash equivalents, program and restricted cash	1	0	0
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	721	883	705	643
Net cash provided by (used in) operating activities	2,380	2,697	2,633
Investing activities
Property and equipment additions	(79)	(67)	(69)
Proceeds received on asset sales	11	7	8
Net assets acquired (net of cash acquired)	(78)	(15)	(51)
intercompany loan receipts	(404)	(264)	(316)
Other, net	(36)	5	2
Net cash used in investing activities exclusive of vehicle programs	(586)	(334)	(426)
Vehicle programs:
Investment In Vehicles	(12,586)	(11,537)	(12,448)
Proceeds received on disposition of vehicles	9,606	9,554	10,473
Repayments of Related Party Debt	(188)	(61)
Proceeds from Related Party Debt	52
Net Cash Used In Investing Activities Of Vehicle Programs	(3,116)	(2,044)	(1,975)
Net cash used in investing activities	(3,702)	(2,378)	(2,401)
Financing activities
Proceeds from borrowings	404	264	337
Principal payments on borrowings	(2)	(194)	(317)
Proceeds from (Repayments of) Short-term Debt	(4)	(4)	4
Debt financing fees	(6)	(4)	(5)
Payments for Repurchase of Common Stock	0	0	0
Intercompany loan borrowings	0	0	(28)
Other, net	(157)	(185)	(75)
Net cash used in financing activities exclusive of vehicle programs	235	(123)	(84)
Vehicle programs:
Proceeds from borrowings	17,339	17,212	15,761
Principal payments on borrowings	(16,373)	(17,259)	(15,817)
Debt financing fees	(25)	(16)	(24)
Net cash provided by financing activities of vehicle programs	941	(63)	(80)
Net cash provided by (used in) financing activities	1,176	(186)	(164)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	(16)	45	(6)
Net (decrease) increase in cash and cash equivalents, program and restricted cash	(162)	178	62
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	(409)	(167)	(342)
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	288
Other, net	0	(320)	(118)
Net cash used in investing activities exclusive of vehicle programs	404	(56)	170
Vehicle programs:
Investment In Vehicles	0	0	0
Proceeds received on disposition of vehicles	0	0	0
Repayments of Related Party Debt	0	0
Proceeds from Related Party Debt	0
Net Cash Used In Investing Activities Of Vehicle Programs	0	0	0
Net cash used in investing activities	404	(56)	170
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)	(288)
Other, net	409	487	460
Net cash used in financing activities exclusive of vehicle programs	5	223	172
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	5	223	172
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	0	0	0
Net (decrease) increase in cash and cash equivalents, program and restricted cash	$ 0	$ 0	$ 0