Pension and Other Postretirement Benefits Pension - Components of Net Periodic Benefit Cost for Defined Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension and other postretirement benefits
Pension settlement and other benefit costs	$ 0.0	$ 0.1	$ 0.0	$ 0.1
SERP settlement loss	0.0	0.1	0.0	0.1
Unallocated corporate costs
Pension and other postretirement benefits
SERP settlement loss		0.1		0.1
Pension Benefits
Pension and other postretirement benefits
Service cost	1.1	1.2	3.5	3.8
Interest cost	3.5	4.0	10.5	12.2
Expected return on plan assets	(5.1)	(5.4)	(15.5)	(15.7)
Recognized net actuarial loss	1.4	1.1	4.0	3.7
Amortization of prior service benefit	0.1	0.1	0.3	0.2
Pension settlement and other benefit costs	0.0	0.1	0.0	0.1
Net periodic benefit cost	1.0	1.1	2.8	4.3
Postretirement Benefits Other than Pensions
Pension and other postretirement benefits
Service cost	0.2	0.3	0.8	0.9
Interest cost	0.3	0.3	0.7	1.1
Expected return on plan assets	0.0	0.0	0.0	0.0
Recognized net actuarial loss	0.1	0.1	0.4	0.5
Amortization of prior service benefit	0.0	0.0	0.0	0.0
Pension settlement and other benefit costs	0.0	0.0	0.0	0.0
Net periodic benefit cost	$ 0.6	$ 0.7	$ 1.9	$ 2.5