Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 12	$ 14
Assets, variable interest entity	608	647
Liabilities, variable interest entity	$ 601	$ 640
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock, shares authorized	300,000,000	300,000,000
Preferred Stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	3,000,000,000	3,000,000,000
Common Stock, shares issued (in shares)	91,886,756	94,558,086
Common Stock, shares outstanding (in shares)	91,886,756	94,558,086