CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Accounts receivable, allowance	$ 43	$ 34
Treasury stock - Common stock, Shares	123,586,000	97,159,000
Common stock
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, Authorized shares	1,600,000,000	1,600,000,000
Common stock, Shares issued	256,276,000	231,493,000
Common stock, Shares outstanding	139,967,000	134,334,000
Class B Common Stock
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, Authorized shares	400,000,000	400,000,000
Common stock, Shares issued	12,800,000	12,800,000
Common stock, Shares outstanding	5,523,000	12,800,000
Treasury stock - Common stock, Shares	7,300,000