Share-Based Compensation - Stock Options Exercise Data (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Summary of stock option exercise data
Cash received			$ 28.3	$ 22.4
Stock options
Summary of stock option exercise data
Number of options exercised	80,650	333,049	213,439	346,549
Cash received	$ 10.8	$ 21.7	$ 28.3	$ 22.4
Total intrinsic value of options exercised	$ 4.7	$ 18.1	$ 9.4	$ 18.7