Guarantor And Non-Guarantor Consolidating Condensed Financial Statements (Consolidating Condensed Statements Of Cash Flows) (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	$ 1,139	$ 1,079
Property and equipment additions	(86)	(89)
Proceeds received on asset sales	4	7
Payments to Acquire Restricted Investments	(14)	(3)
Proceeds from (Repayments of) Related Party Debt	0	0
Other, net	(1)	4
Net cash used in investing activities exclusive of vehicle programs	(97)	(81)
Decrease (increase) in program cash	168	82
Investment in vehicles	(8,116)	(8,500)
Proceeds received on disposition of vehicles	5,059	5,418
Repayments of Related Party Debt	(33)	0
Net cash used in investing activities of vehicle programs	(2,922)	(3,000)
Net cash used in investing activities	(3,019)	(3,081)
Proceeds from long-term borrowings	589	558
Principal payments on borrowings	(591)	(520)
Proceeds from (Repayments of) Short-term Debt	(1)
Net change in short-term borrowings	(1)	0
Intercompany loan borrowings	0	0
Repurchases of common stock	(109)	(183)
Debt financing fees	(8)	(10)
Other, net	0	0
Net cash provided by financing activities exclusive of vehicle programs	(120)	(155)
Proceeds from borrowings	11,255	9,850
Principal payments on borrowings	(8,988)	(7,614)
Debt financing fees	(8)	(17)
Net cash provided by financing activities of vehicle programs	2,259	2,219
Net cash provided by financing activities	2,139	2,064
Effect of changes in exchange rates on cash and cash equivalents	27	13
Net increase in cash and cash equivalents	286	75
Cash and cash equivalents, beginning of period	490	452
Cash and cash equivalents, end of period	776	527
Eliminations [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	0	(80)
Property and equipment additions	0	0
Proceeds received on asset sales	0	0
Payments to Acquire Restricted Investments	0	0
Proceeds from (Repayments of) Related Party Debt	314	(28)
Other, net	(100)	(93)
Net cash used in investing activities exclusive of vehicle programs	214	(121)
Decrease (increase) in program cash	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	214	(121)
Proceeds from long-term borrowings	0	0
Principal payments on borrowings	0	0
Proceeds from (Repayments of) Short-term Debt	0
Intercompany loan borrowings	(314)	28
Repurchases of common stock		0
Debt financing fees	0	0
Other, net	100	173
Net cash provided by financing activities exclusive of vehicle programs	(214)	201
Proceeds from borrowings	0	0
Principal payments on borrowings	0	0
Debt financing fees	0
Net cash provided by financing activities of vehicle programs	0	0
Net cash provided by financing activities	(214)	201
Effect of changes in exchange rates on cash and cash equivalents	0	0
Net increase in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Parent Company [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	9	89
Property and equipment additions	0	0
Proceeds received on asset sales	0	0
Payments to Acquire Restricted Investments	0	0
Proceeds from (Repayments of) Related Party Debt	0	0
Other, net	100	93
Net cash used in investing activities exclusive of vehicle programs	100	93
Decrease (increase) in program cash	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	100	93
Proceeds from long-term borrowings	0	0
Principal payments on borrowings	0	0
Proceeds from (Repayments of) Short-term Debt	0
Intercompany loan borrowings	0	0
Repurchases of common stock	(109)	(183)
Debt financing fees	0	0
Other, net	0	0
Net cash provided by financing activities exclusive of vehicle programs	(109)	(183)
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	(109)	(183)
Effect of changes in exchange rates on cash and cash equivalents	0	0
Net increase in cash and cash equivalents	0	(1)
Cash and cash equivalents, beginning of period	3	4
Cash and cash equivalents, end of period	3	3
Subsidiaries [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	(41)	144
Property and equipment additions	(22)	(11)
Proceeds received on asset sales	1	4
Payments to Acquire Restricted Investments	0	0
Proceeds from (Repayments of) Related Party Debt	0	0
Other, net	0	0
Net cash used in investing activities exclusive of vehicle programs	(21)	(7)
Decrease (increase) in program cash	0	0
Investment in vehicles	1	(2)
Proceeds received on disposition of vehicles	31	20
Repayments of Related Party Debt	0
Net cash used in investing activities of vehicle programs	32	18
Net cash used in investing activities	11	11
Proceeds from long-term borrowings	325	557
Principal payments on borrowings	(396)	(518)
Proceeds from (Repayments of) Short-term Debt	0
Intercompany loan borrowings	313	0
Repurchases of common stock	0	0
Debt financing fees	(3)	(10)
Other, net	(100)	(173)
Net cash provided by financing activities exclusive of vehicle programs	139	(144)
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	139	(144)
Effect of changes in exchange rates on cash and cash equivalents	0	0
Net increase in cash and cash equivalents	109	11
Cash and cash equivalents, beginning of period	12	70
Cash and cash equivalents, end of period	121	81
Guarantor Subsidiaries [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	47	30
Property and equipment additions	(34)	(46)
Proceeds received on asset sales	0	1
Payments to Acquire Restricted Investments	(4)	(1)
Proceeds from (Repayments of) Related Party Debt	(1)	28
Other, net	0	0
Net cash used in investing activities exclusive of vehicle programs	(39)	(18)
Decrease (increase) in program cash	0	0
Investment in vehicles	(2)	(7)
Proceeds received on disposition of vehicles	0	0
Repayments of Related Party Debt	0
Net cash used in investing activities of vehicle programs	(2)	(7)
Net cash used in investing activities	(41)	(25)
Proceeds from long-term borrowings	0	0
Principal payments on borrowings	(1)	(1)
Proceeds from (Repayments of) Short-term Debt	0
Intercompany loan borrowings	0	0
Repurchases of common stock	0	0
Debt financing fees	0	0
Other, net	0	0
Net cash provided by financing activities exclusive of vehicle programs	(1)	(1)
Proceeds from borrowings	0	0
Principal payments on borrowings	(5)	(4)
Debt financing fees	0	0
Net cash provided by financing activities of vehicle programs	(5)	(4)
Net cash provided by financing activities	(6)	(5)
Effect of changes in exchange rates on cash and cash equivalents	0	0
Net increase in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Subsidiaries Non Guarantor [Member]
Supplemental Guarantor Financial Information [Line Items]
Net cash provided by (used in) operating activities	1,124	896
Property and equipment additions	(30)	(32)
Proceeds received on asset sales	3	2
Payments to Acquire Restricted Investments	(10)	(2)
Proceeds from (Repayments of) Related Party Debt	(313)	0
Other, net	(1)	4
Net cash used in investing activities exclusive of vehicle programs	(351)	(28)
Decrease (increase) in program cash	168	82
Investment in vehicles	(8,115)	(8,491)
Proceeds received on disposition of vehicles	5,028	5,398
Repayments of Related Party Debt	(33)
Net cash used in investing activities of vehicle programs	(2,952)	(3,011)
Net cash used in investing activities	(3,303)	(3,039)
Proceeds from long-term borrowings	264	1
Principal payments on borrowings	(194)	(1)
Proceeds from (Repayments of) Short-term Debt	(1)
Intercompany loan borrowings	1	(28)
Repurchases of common stock	0	0
Debt financing fees	(5)	0
Other, net	0	0
Net cash provided by financing activities exclusive of vehicle programs	65	(28)
Proceeds from borrowings	11,255	9,850
Principal payments on borrowings	(8,983)	(7,610)
Debt financing fees	(8)	(17)
Net cash provided by financing activities of vehicle programs	2,264	2,223
Net cash provided by financing activities	2,329	2,195
Effect of changes in exchange rates on cash and cash equivalents	27	13
Net increase in cash and cash equivalents	177	65
Cash and cash equivalents, beginning of period	475	378
Cash and cash equivalents, end of period	$ 652	$ 443