Summary of Geographic Segment Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	$ 8,848	$ 8,659	$ 8,502
Assets exclusive of assets under vehicle programs	5,820	6,065	5,918
Assets under vehicle programs	11,879	11,578	11,716
Long-Lived Assets	2,627	2,562	2,571
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	5,629	5,674	5,635
Assets exclusive of assets under vehicle programs	3,069	3,699	3,677
Assets under vehicle programs	8,192	8,552	8,786
Long-Lived Assets	1,451	1,489	1,502
All Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	3,219	2,985	2,867
Assets exclusive of assets under vehicle programs	2,751	2,366	2,241
Assets under vehicle programs	3,687	3,026	2,930
Long-Lived Assets	$ 1,176	$ 1,073	$ 1,069