Summary of Segments Information (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 2,162	$ 2,753	$ 2,337	$ 1,920	$ 2,050	$ 2,778	$ 2,328	$ 1,968	$ 9,172	$ 9,124	$ 8,848
Vehicle depreciation and lease charges, net									2,063	2,179	2,221
Vehicle interest, net									(344)	(314)	(286)
Adjusted EBITDA									788	781	735
Non-vehicle depreciation and amortization									263	256	259
Assets exclusive of assets under vehicle programs	9,311				6,370				9,311	6,370	5,820
Assets under vehicle programs	13,815				12,779				13,815	12,779	11,879
Capital expenditures (excluding vehicles)									250	231	197
Americas
Segment Reporting Information [Line Items]
Revenues									6,352	6,186	6,100
Vehicle depreciation and lease charges, net									1,462	1,568	1,671
Vehicle interest, net									(284)	(252)	(226)
Adjusted EBITDA									652	558	486
Non-vehicle depreciation and amortization									161	152	168
Assets exclusive of assets under vehicle programs	6,226				3,782				6,226	3,782	3,388
Assets under vehicle programs	10,508				9,670				10,508	9,670	9,017
Capital expenditures (excluding vehicles)									162	134	122
International
Segment Reporting Information [Line Items]
Revenues									2,820	2,938	2,748
Vehicle depreciation and lease charges, net									601	611	550
Vehicle interest, net									(60)	(62)	(60)
Adjusted EBITDA									203	287	305
Non-vehicle depreciation and amortization									94	104	91
Assets exclusive of assets under vehicle programs	2,995				2,495				2,995	2,495	2,353
Assets under vehicle programs	3,307				3,109				3,307	3,109	2,862
Capital expenditures (excluding vehicles)									62	76	62
Corporate and Other
Segment Reporting Information [Line Items]
Revenues									0
Vehicle depreciation and lease charges, net									0
Vehicle interest, net									0
Adjusted EBITDA									(67)	(64)	(56)
Non-vehicle depreciation and amortization									8
Assets exclusive of assets under vehicle programs	90				$ 93				90	93	79
Assets under vehicle programs	$ 0								0
Capital expenditures (excluding vehicles)									26	21	13
Acquisition-related Costs [Member]
Segment Reporting Information [Line Items]
Non-vehicle depreciation and amortization									$ 56	$ 61	$ 58