CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
ASSETS
Allowance for doubtful accounts	$ 115	$ 108
LIABILITIES AND STOCKHOLDERS’ EQUITY
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	114,406,501	114,210,157
Common stock, shares outstanding (in shares)	72,392,992	72,196,648
Treasury stock, shares (in shares)	42,013,509	42,013,509