Share-Based Compensation - Stock Options Exercise Data (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Summary of stock option exercise data
Cash received			$ 42.3	$ 25.9
Stock options
Summary of stock option exercise data
Number of options exercised (in shares)	107,233	54,834	320,672	401,383
Cash received	$ 14.0	$ 3.5	$ 42.3	$ 25.9
Total intrinsic value of options exercised	$ 8.0	$ 3.1	$ 17.4	$ 21.8