Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	May 20, 2019	May 19, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowances for doubtful accounts	$ 25.0			$ 27.4	$ 28.6	$ 53.3
Preferred stock, par value (in dollars per shares)	$ 0.01			$ 0.01
Preferred stock, shares authorized	500,000.0			500,000.0
Preferred stock, shares issued	0			0	0
Treasury stock, shares	1,600,000			2,700,000
Common Class A
Common stock, par value (in dollars per share)	$ 0.025			$ 0.025
Common stock, shares authorized	105,000,000.0	105,000,000.0	80,000,000.0	105,000,000
Common stock, shares issued	40,300,000			40,300,000	40,000,000.0
Treasury stock, shares	1,100,000			2,200,000	1,800,000
Common Class B
Common stock, par value (in dollars per share)	$ 0.025			$ 0.025
Common stock, shares authorized	80,000,000.0			80,000,000
Common stock, shares issued	13,500,000			13,500,000	13,800,000
Treasury stock, shares	0			0	0
Common Class C
Common stock, par value (in dollars per share)	$ 0.025			$ 0.025
Common stock, shares authorized	20,000,000.0			20,000,000
Common stock, shares issued	500,000			500,000	500,000
Treasury stock, shares	500,000			500,000	500,000