Summary of Geographic Segment 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
Revenues from External Customers and Long-Lived Assets [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
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
Long-Lived Assets	2,691				2,653				2,691	2,653	2,627
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									5,867	5,708	5,629
Assets exclusive of assets under vehicle programs	5,830				3,494				5,830	3,494	3,069
Assets under vehicle programs	9,824				9,021				9,824	9,021	8,192
Long-Lived Assets	1,536				1,476				1,536	1,476	1,451
All Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									3,305	3,416	3,219
Assets exclusive of assets under vehicle programs	3,481				2,876				3,481	2,876	2,751
Assets under vehicle programs	3,991				3,758				3,991	3,758	3,687
Long-Lived Assets	$ 1,155				$ 1,177				$ 1,155	$ 1,177	$ 1,176