CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
CONSOLIDATED BALANCE SHEETS
Trade receivables allowance	$ 34	$ 32
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	185,727,663	185,354,796
Treasury stock, shares	22,648,606	23,017,367