Pensions and Postretirement Benefits (Summary of Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Components of net periodic benefit cost
Service costs	$ 4.1	$ 3.8	$ 3.7
Interest costs	2.1	2.6	2.2
Expected return on plan assets	(11.7)	(10.9)	(11.6)
Amortization of prior service cost (credit)	0.0	0.0	0.0
Recognized net actuarial loss	1.9	2.2	0.3
Benefit (income) costs	(3.6)	(2.3)	(5.4)
Other changes in plan assets and benefit obligations recognized in accumulated other comprehensive (income) loss (“AOCI”)
AOCI at beginning of year	28.3	35.0	16.8
Net (loss) gain arising during the year	(1.8)	(2.2)	(0.3)
Recognition of prior service credit	0.0	0.0	0.0
Recognition of actuarial loss	(5.0)	(4.5)	18.5
Total recognized in accumulated other comprehensive loss at end of year	21.5	28.3	35.0
Postretirement Benefits
Components of net periodic benefit cost
Service costs	0.0	0.0	0.0
Interest costs	0.2	0.3	0.3
Expected return on plan assets	0.0	0.0	0.0
Amortization of prior service cost (credit)	0.0	(0.1)	(0.1)
Recognized net actuarial loss	0.2	0.3	0.1
Benefit (income) costs	0.4	0.5	0.3
Other changes in plan assets and benefit obligations recognized in accumulated other comprehensive (income) loss (“AOCI”)
AOCI at beginning of year	2.6	2.3	2.0
Net (loss) gain arising during the year	(0.2)	(0.3)	(0.1)
Recognition of prior service credit	0.0	0.1	0.1
Recognition of actuarial loss	0.6	0.5	0.3
Total recognized in accumulated other comprehensive loss at end of year	$ 3.0	$ 2.6	$ 2.3