Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Consolidated Balance Sheets
Accounts receivable, allowance for doubtful accounts	$ 44.8	$ 33.6
Class A Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Class A Common Stock, shares authorized	1,000.0	1,000.0
Class A Common Stock, shares issued	300.3	298.7
Class A Common Stock, shares outstanding	299.3	297.9
Treasury stock, shares	1.0	0.8