Pension and Postretirement Benefits - Components of Net Periodic (Income) Cost Associated with Pension Plans and Postretirement Benefit Obligations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.4	$ 0.7	$ 1.2	$ 2.3
Interest cost	16.3	8.8	48.4	26.4
Expected return on plan assets	(20.2)	(19.6)	(60.1)	(59.4)
Amortization of prior service cost (credit)	0.0	0.0	0.0	0.0
Amortization of actuarial loss (gain)	(0.6)	0.0	(1.8)	0.0
Net periodic cost (income)	(4.1)	(10.1)	(12.3)	(30.7)
Postretirement benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	0.0	0.0	0.0	0.0
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of prior service cost (credit)	(0.1)	(0.1)	(0.3)	(0.3)
Amortization of actuarial loss (gain)	0.0	0.0	0.0	0.0
Net periodic cost (income)	$ (0.1)	$ (0.1)	$ (0.3)	$ (0.3)