Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 116	$ 111
Other intangible assets, accumulated amortization	534	519
Service Concession Asset, Accumulated Depreciation	$ 136	$ 114
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,200,000,000	1,200,000,000
Common stock, shares issued (in shares)	816,079,347	816,061,123
Common stock, shares outstanding (in shares)	660,108,793	659,182,232
Treasury stock, shares (in shares)	155,970,554	156,878,891
Variable Interest Entity [Line Items]
Non-recourse debt - current, balance at variable interest entities	$ 1,137	$ 1,303
Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Non-recourse debt - current, balance at variable interest entities	134	273
Non-recourse debt - noncurrent, balance at variable interest entities	$ 1,643	$ 1,502