CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
CONSOLIDATED BALANCE SHEETS
Trade receivables allowance	$ 35	$ 34
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	186,575,999	185,727,663
Treasury stock, shares	30,917,603	22,648,606