Share-based Compensation Awards (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based Payment Award
Vesting period in which the fair value of shares on grant date is amortized over, years	2 years
Stock-settled awards
Stock-based Payment Award
Awards granted	0.9	2.3	2.5
Weighted-average grant-date fair value (per award)	$ 26.96	$ 20.70	$ 22.78
Total fair value of vested awards distributed	$ 50.8	$ 17.3	$ 15.2
Accrued dividends on non-vested stock-settled awards	3.6	5.6
Dividends paid for stock-settled awards	$ 4.3	$ 1.5
Cash-settled awards
Stock-based Payment Award
Awards granted	0.0	0.0	0.0
Weighted-average grant-date fair value (per award)	$ 0	$ 21.02	$ 22.83
Total fair value of vested awards distributed	$ 0.7	$ 0.3	$ 0.9
Performance-based awards
Stock-based Payment Award
Awards granted	0.5	2.4	2.1
Weighted-average grant-date fair value (per award)	$ 21.98	$ 18.67	$ 20.16
Total fair value of vested awards distributed	$ 39.3	$ 53.3	$ 64.9