Pension and Other Post-Retirement Benefits - Components of Net Periodic Cost (Benefit) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Defined Benefit Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.9	$ 2.2	$ 3.9	$ 4.4
Interest cost	2.3	2.0	4.9	4.0
Expected return on plan assets	(3.8)	(4.6)	(7.8)	(9.3)
Settlement accounting adjustment	0.9		0.9
Unrecognized prior service credit	0.0		0.0
Unrecognized net actuarial loss (gain)	2.4	3.2	4.6	6.6
Net periodic cost	3.7	2.8	6.5	5.7
Retiree Health and Life [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.1	0.1
Interest cost	0.1	0.0	0.2	0.1
Expected return on plan assets	0.0	0.0	0.0	0.0
Unrecognized prior service credit	(0.1)	(0.1)	(0.1)	(0.1)
Unrecognized net actuarial loss (gain)	(0.1)	0.0	(0.2)	(0.1)
Net periodic cost	$ 0.0	$ 0.0	$ 0.0	$ 0.0