Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits
Pension and other postretirement benefits
Service cost	$ 1.2	$ 1.3	$ 2.4	$ 2.6
Interest cost	3.5	4.1	7.0	8.2
Expected return on plan assets	(5.2)	(5.3)	(10.4)	(10.3)
Recognized net actuarial loss	1.3	1.1	2.6	2.6
Amortization of prior service benefit	0.1	0.1	0.2	0.1
Net periodic benefit cost	0.9	1.3	1.8	3.2
Postretirement Benefits Other than Pensions
Pension and other postretirement benefits
Service cost	0.3	0.3	0.6	0.6
Interest cost	0.2	0.4	0.4	0.8
Expected return on plan assets	0.0	0.0	0.0	0.0
Recognized net actuarial loss	0.1	0.2	0.3	0.4
Amortization of prior service benefit	0.0	0.0	0.0	0.0
Net periodic benefit cost	$ 0.6	$ 0.9	$ 1.3	$ 1.8