CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accounts receivable, allowance for doubtful accounts	$ 8	$ 2
Class A Common Stock
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)	66,830,110	68,897,723
Common Stock, shares outstanding (in shares)	66,830,110	68,897,723
Class B Common Stock
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	140,000,000	140,000,000
Common Stock, shares issued (in shares)	24,727,682	25,670,684
Common Stock, shares outstanding (in shares)	24,727,682	25,670,684