Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 76	$ 69
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	1,000,000,000	1,000,000,000
Common stock, outstanding	169,535,729	168,754,605