Summary of Segments Information (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 2,050	$ 2,778	$ 2,328	$ 1,968	$ 2,019	$ 2,752	$ 2,238	$ 1,839	$ 9,124	$ 8,848	$ 8,659
Vehicle depreciation and lease charges, net									2,179	2,221	2,047
Vehicle interest, net									(314)	(286)	(284)
Adjusted EBITDA									781	735	838
Non-vehicle depreciation and amortization									256	259	253
Assets exclusive of assets under vehicle programs	6,370				5,820				6,370	5,820	6,065
Assets under vehicle programs	12,779				11,879				12,779	11,879	11,578
Capital expenditures (excluding vehicles)									231	197	190
Americas
Segment Reporting Information [Line Items]
Revenues									6,186	6,100	6,121
Vehicle depreciation and lease charges, net									1,568	1,671	1,559
Vehicle interest, net									(252)	(226)	(226)
Adjusted EBITDA									558	486	633
Non-vehicle depreciation and amortization									152	168	165
Assets exclusive of assets under vehicle programs	3,782				3,388				3,782	3,388	4,017
Assets under vehicle programs	9,670				9,017				9,670	9,017	9,210
Capital expenditures (excluding vehicles)									134	122	121
International
Segment Reporting Information [Line Items]
Revenues									2,938	2,748	2,538
Vehicle depreciation and lease charges, net									611	550	488
Vehicle interest, net									(62)	(60)	(58)
Adjusted EBITDA									287	305	273
Non-vehicle depreciation and amortization									104	91	88
Assets exclusive of assets under vehicle programs	2,495				2,353				2,495	2,353	1,990
Assets under vehicle programs	3,109				2,862				3,109	2,862	2,368
Capital expenditures (excluding vehicles)									76	62	62
Corporate and Other
Segment Reporting Information [Line Items]
Adjusted EBITDA									(64)	(56)	(68)
Assets exclusive of assets under vehicle programs	$ 93				$ 79				93	79	58
Capital expenditures (excluding vehicles)									21	13	7
Acquisition-related Costs [Member]
Segment Reporting Information [Line Items]
Non-vehicle depreciation and amortization									$ 61	$ 58	$ 59