Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension and other postretirement benefits
Amount of settlement loss recognized (b)	$ 0.0	$ 0.8
Pension Benefits
Pension and other postretirement benefits
Service cost	1.3	1.7
Interest cost	4.1	4.0
Expected return on plan assets	(5.0)	(5.3)
Recognized net actuarial loss	1.5	1.3
Amortization of prior service benefit	0.1	0.1
Amount of settlement loss recognized (b)	0.0	0.8
Net periodic benefit cost	2.0	2.6
Postretirement Benefits Other than Pensions
Pension and other postretirement benefits
Service cost	0.3	0.3
Interest cost	0.4	0.3
Expected return on plan assets	0.0	0.0
Recognized net actuarial loss	0.2	0.2
Amortization of prior service benefit	0.0	0.0
Amount of settlement loss recognized (b)	0.0	0.0
Net periodic benefit cost	$ 0.9	$ 0.8