CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 103	$ 93
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	113,825,667	112,907,209
Common stock, shares outstanding	74,362,195	79,872,956
Treasury stock, shares	39,463,472	33,034,253