Guarantor And Non-Guarantor Consolidating Condensed Financial Statements (Consolidating Condensed Statements Of Cash Flows) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	$ 440	$ 503
Property and equipment additions	(57)	(57)
Proceeds received on asset sales	2	4
Payments to Acquire Restricted Investments	(5)	(10)
Other, net	(3)	(19)
Net cash used in investing activities exclusive of vehicle programs	(63)	(82)
Investment in vehicles	(4,376)	(4,226)
Proceeds received on disposition of vehicles	3,083	2,572
Repayments of Related Party Debt	(78)	0
Net cash used in investing activities of vehicle programs	(1,371)	(1,654)
Net cash used in investing activities	(1,434)	(1,736)
Proceeds from long-term borrowings	0	81
Principal payments on borrowings	(5)	(89)
Proceeds from (Repayments of) Short-term Debt	0	(1)
Repurchases of common stock	(4)	(14)
Debt financing fees	0	(8)
Other, net	0	1
Net cash provided by financing activities exclusive of vehicle programs	(9)	(30)
Proceeds from borrowings	5,989	5,100
Principal payments on borrowings	(5,038)	(4,045)
Debt financing fees	(5)	(1)
Net cash provided by financing activities of vehicle programs	946	1,054
Net cash provided by financing activities	937	1,024
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	(2)	9
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(59)	(200)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	676	701	$ 735	$ 901
Eliminations [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	0	(7)
Property and equipment additions	0	0
Proceeds received on asset sales	0	0
Payments to Acquire Restricted Investments	0	0
Other, net	0	0
Net cash used in investing activities exclusive of vehicle programs	0	0
Investment in vehicles	0	0
Proceeds received on disposition of vehicles	0	0
Repayments of Related Party Debt	0
Net cash used in investing activities of vehicle programs	0	0
Net cash used in investing activities	0	0
Proceeds from long-term borrowings		0
Principal payments on borrowings	0	0
Proceeds from (Repayments of) Short-term Debt		0
Repurchases of common stock	0	0
Debt financing fees		0
Other, net		7
Net cash provided by financing activities exclusive of vehicle programs	0	7
Proceeds from borrowings	0	0
Principal payments on borrowings	0	0
Debt financing fees	0	0
Net cash provided by financing activities of vehicle programs	0	0
Net cash provided by financing activities	0	7
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0	0
Non-Guarantor Subsidiaries [Member]
Supplemental Guarantor Financial Information [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	664	675
Parent Company [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	4	12
Property and equipment additions	0	0
Proceeds received on asset sales	0	0
Payments to Acquire Restricted Investments	0	0
Other, net	0	0
Net cash used in investing activities exclusive of vehicle programs	0	0
Investment in vehicles	0	0
Proceeds received on disposition of vehicles	0	0
Repayments of Related Party Debt	0
Net cash used in investing activities of vehicle programs	0	0
Net cash used in investing activities	0	0
Proceeds from long-term borrowings		0
Principal payments on borrowings	0	0
Proceeds from (Repayments of) Short-term Debt		0
Repurchases of common stock	(4)	(14)
Debt financing fees		0
Other, net		1
Net cash provided by financing activities exclusive of vehicle programs	(4)	(13)
Proceeds from borrowings	0	0
Principal payments on borrowings	0	0
Debt financing fees	0	0
Net cash provided by financing activities of vehicle programs	0	0
Net cash provided by financing activities	(4)	(13)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	0	(1)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1	3	1	4
Subsidiaries [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	5	41
Property and equipment additions	(16)	(15)
Proceeds received on asset sales	0	2
Payments to Acquire Restricted Investments	0	(3)
Other, net	0	0
Net cash used in investing activities exclusive of vehicle programs	(16)	(16)
Investment in vehicles	(1)	0
Proceeds received on disposition of vehicles	13	7
Repayments of Related Party Debt	0
Net cash used in investing activities of vehicle programs	12	7
Net cash used in investing activities	(4)	(9)
Proceeds from long-term borrowings		81
Principal payments on borrowings	(4)	(88)
Proceeds from (Repayments of) Short-term Debt		0
Repurchases of common stock	0	0
Debt financing fees		(8)
Other, net		(7)
Net cash provided by financing activities exclusive of vehicle programs	(4)	(22)
Proceeds from borrowings	0	0
Principal payments on borrowings	(1)	(1)
Debt financing fees	0	0
Net cash provided by financing activities of vehicle programs	(1)	(1)
Net cash provided by financing activities	(5)	(23)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(4)	9
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	8	23	12	14
Guarantor Subsidiaries [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	34	30
Property and equipment additions	(25)	(23)
Proceeds received on asset sales	0	0
Payments to Acquire Restricted Investments	(4)	(3)
Other, net	0	0
Net cash used in investing activities exclusive of vehicle programs	(29)	(26)
Investment in vehicles	0	(1)
Proceeds received on disposition of vehicles	0	0
Repayments of Related Party Debt	0
Net cash used in investing activities of vehicle programs	0	(1)
Net cash used in investing activities	(29)	(27)
Proceeds from long-term borrowings		0
Principal payments on borrowings	0	(1)
Proceeds from (Repayments of) Short-term Debt		0
Repurchases of common stock	0	0
Debt financing fees		0
Other, net		0
Net cash provided by financing activities exclusive of vehicle programs	0	(1)
Proceeds from borrowings	0	0
Principal payments on borrowings	(3)	(2)
Debt financing fees	0	0
Net cash provided by financing activities of vehicle programs	(3)	(2)
Net cash provided by financing activities	(3)	(3)
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	2	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	3	0	1	0
Subsidiaries Non Guarantor [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	397	427
Property and equipment additions	(16)	(19)
Proceeds received on asset sales	2	2
Payments to Acquire Restricted Investments	(1)	(4)
Other, net	(3)	(19)
Net cash used in investing activities exclusive of vehicle programs	(18)	(40)
Investment in vehicles	(4,375)	(4,225)
Proceeds received on disposition of vehicles	3,070	2,565
Repayments of Related Party Debt	(78)
Net cash used in investing activities of vehicle programs	(1,383)	(1,660)
Net cash used in investing activities	(1,401)	(1,700)
Proceeds from long-term borrowings		0
Principal payments on borrowings	(1)	0
Proceeds from (Repayments of) Short-term Debt		(1)
Repurchases of common stock	0	0
Debt financing fees		0
Other, net		0
Net cash provided by financing activities exclusive of vehicle programs	(1)	(1)
Proceeds from borrowings	5,989	5,100
Principal payments on borrowings	(5,034)	(4,042)
Debt financing fees	(5)	(1)
Net cash provided by financing activities of vehicle programs	950	1,057
Net cash provided by financing activities	949	1,056
Effect of changes in exchange rates on cash and cash equivalents, program and restricted cash	(2)	9
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(57)	(208)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 664	$ 675	$ 721	$ 883