CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Accounts receivable, allowance	$ 98	$ 101
Treasury stock (in shares)	131,141,000	130,767,000
Series A Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	100,000,000	100,000,000
Preferred stock, shares issued (in shares)	1,200,000	1,200,000
Preferred stock, shares outstanding (in shares)	1,200,000	1,200,000
Class B Common Stock
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, authorized shares (in shares)	400,000,000	400,000,000
Common stock, shares issued (in shares)	12,800,000	12,800,000
Common stock, shares outstanding (in shares)	5,523,000	5,523,000
Treasury stock (in shares)	7,300,000	7,300,000
Common stock
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, authorized shares (in shares)	1,600,000,000	1,600,000,000
Common stock, shares issued (in shares)	265,207,000	261,564,000
Common stock, shares outstanding (in shares)	141,342,000	138,074,000