Income Taxes - Components of the provision for income taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
Federal									$ 7.6	$ (5.4)	$ 29.3
State									3.0	0.8	0.5
Foreign									5.6	1.5	0.3
Total current									16.2	(3.1)	30.1
Deferred:
Effect of tax cuts and jobs act - Deferred federal									0.0	(1.5)	(6.2)
Other - Deferred federal									22.6	24.8	16.6
Federal									22.6	23.3	10.4
State									(0.6)	5.4	0.9
Foreign									(4.7)	(6.3)	(1.0)
Total deferred									17.3	22.4	10.3
Provision (benefit) for income taxes	$ 7.4	$ 9.2	$ 9.0	$ 7.9	$ 1.1	$ 3.4	$ 6.8	$ 8.0	$ 33.5	$ 19.3	$ 40.4