CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (PARENTHETICAL) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 18	$ 20
Accumulated depreciation	$ 2,012	$ 1,952
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	6,000,000,000	6,000,000,000
Common stock issued, shares	501,891,243	501,891,243
Common stock, shares outstanding	474,973,405	475,317,751
Treasury stock, shares	26,917,838	26,573,492
Restricted cash	$ 2	$ 2