Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 23	$ 23
Other intangible assets, accumulated amortization	467	457
Service Concession Asset, Accumulated Depreciation	$ 0	$ 0
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)	817,593,854	817,203,691
Common stock, shares outstanding (in shares)	663,694,956	662,298,096
Treasury stock, shares (in shares)	153,898,898	154,905,595
Variable Interest Entity [Line Items]
Non Recourse Debt Non Current	$ 14,550	$ 13,986
Non-recourse debt, including $338 and $479, respectively, related to variable interest entities	1,265	1,659
Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Non Recourse Debt Non Current	3,077	2,922
Non-recourse debt, including $338 and $479, respectively, related to variable interest entities	$ 338	$ 479