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Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Statement of Financial Position [Abstract]    
Allowance for doubtful accounts $ 10 $ 11
Common stock, par value $ 0.01 $ 0.01
Common stock, shares authorized 400,000,000 400,000,000
Common stock, shares outstanding 128,755,023 131,636,870
Preferred stock, par value $ 0.01 $ 0.01
Preferred stock, shares authorized 50,000,000 50,000,000
Preferred stock, shares outstanding 0 0