Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Condensed Consolidated Balance Sheets
Allowance for doubtful accounts	$ 5.7	$ 5.3
Accumulated depreciation	$ 738.6	$ 665.7
Ordinary shares, nominal value	$ 0.01	$ 0.01
Ordinary shares, shares authorized	50,000,000,000.0	50,000,000,000.0
Ordinary shares, shares issued	48,800,000	48,800,000
Ordinary shares, shares outstanding	38,300,000	39,000,000.0
Treasury stock, shares	10,500,000	9,800,000