Segment Information (Summary Of Segments Information) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets Under Vehicle Programs	$ 14,726		$ 14,726		$ 11,879
Document Fiscal Year Focus			2018
Revenues	2,328	$ 2,238	$ 4,296	$ 4,077
Revenues	2,328	2,238	4,296	4,077
Adjusted EBITDA	161	140	163	113
Non-vehicle related depreciation and amortization	67	65	128	128
Interest expense	49	48	95	97
Early extinguishment of debt	0	0	(5)	(3)
Non-operational charges related to shareholder activist activity			9	0
Restructuring Charges	4	38	10	45
Transaction-related costs, net	3	5	7	8
Charges for legal matter	0	(27)	0	(14)
Income before income taxes	38	11	(91)	(154)
Americas
Segment Reporting Information [Line Items]
Assets Under Vehicle Programs	11,000		11,000		9,000
Adjusted EBITDA	107	96	122	76
International [Member]
Segment Reporting Information [Line Items]
Assets Under Vehicle Programs	3,700		3,700		$ 2,900
Revenues	738	673	1,358	1,198
Adjusted EBITDA	71	59	74	66
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Adjusted EBITDA	(17)	(15)	(33)	(29)
Americas
Segment Reporting Information [Line Items]
Revenues	$ 1,590	$ 1,565	$ 2,938	$ 2,879