Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Pension and other postretirement benefits
Aggregate contributions to qualified and non-qualified pension trusts and payments of pension benefits for unfunded pension plans	$ 1.2	$ 0.5	$ 18.4
Pension Benefits
Pension and other postretirement benefits
Service cost	1.3	1.2
Interest cost	3.7	4.0
Expected return on plan assets	(4.8)	(4.7)
Recognized net actuarial loss	1.9	1.7
Amortization of prior service benefit	0.1	0.0
Net periodic benefit cost	2.2	2.2
Expected 2017 aggregate contributions to qualified and non-qualified pension trusts and payments of pension benefits for unfunded pension plans	16.0
Postretirement Benefits Other than Pensions
Pension and other postretirement benefits
Service cost	0.3	0.3
Interest cost	0.4	0.4
Expected return on plan assets	0.0	0.0
Recognized net actuarial loss	0.0	0.1
Amortization of prior service benefit	0.0	(0.1)
Net periodic benefit cost	$ 0.7	$ 0.7