Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 10	$ 17
Other intangible assets, accumulated amortization	441	399
Service Concession Asset, Accumulated Depreciation	$ 206	$ 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)	816,312,913	816,061,123
Common stock, shares outstanding (in shares)	660,388,128	659,182,232
Treasury stock, shares (in shares)	155,924,785	156,878,891
Variable Interest Entity [Line Items]
Non-recourse debt - current balance at variable interest entities	$ 2,164	$ 1,052
Non-recourse debt - noncurrent, balance at variable interest entities	13,176	13,731
Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Non-recourse debt - current balance at variable interest entities	1,012	273
Non-recourse debt - noncurrent, balance at variable interest entities	$ 1,358	$ 1,502