Employee Retirement Plans and Postretirement Benefits - Net Periodic Pension (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 162.9	$ 120.0
Total other pension and postretirement (benefit) cost, net	(10.2)	(36.6)	$ (46.4)
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.9	1.3	2.7
Interest cost	140.4	103.9	93.9
Expected return on plan assets, net of expenses	(157.8)	(154.2)	(161.6)
Amortization of prior service (benefit) cost	0.3	0.3	0.4
Amortization of net actuarial (gain) loss	17.1	5.6	8.7
Curtailment, settlement or special termination benefit (gain) loss	0.0	2.9	5.4
Expected participant contributions	(0.3)	(0.3)	(0.4)
Total other pension and postretirement (benefit) cost, net	(0.3)	(41.8)	(53.6)
Net periodic pension and OPEB (benefit) cost	0.6	(40.5)	(50.9)
Pension | Canadian Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Curtailment, settlement or special termination benefit (gain) loss		8.0
Pension | U.S. Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Curtailment, settlement or special termination benefit (gain) loss		(5.3)
OPEB
Defined Benefit Plan Disclosure [Line Items]
Service cost	3.3	5.5	6.0
Interest cost	22.5	16.1	14.6
Expected return on plan assets, net of expenses	0.0	0.0	0.0
Amortization of prior service (benefit) cost	(0.7)	(0.7)	(0.7)
Amortization of net actuarial (gain) loss	(31.7)	(10.2)	(6.7)
Curtailment, settlement or special termination benefit (gain) loss	0.0	0.0	0.0
Expected participant contributions	0.0	0.0	0.0
Total other pension and postretirement (benefit) cost, net	(9.9)	5.2	7.2
Net periodic pension and OPEB (benefit) cost	(6.6)	10.7	13.2
Consolidated
Defined Benefit Plan Disclosure [Line Items]
Service cost	4.2	6.8	8.7
Interest cost	162.9	120.0	108.5
Expected return on plan assets, net of expenses	(157.8)	(154.2)	(161.6)
Amortization of prior service (benefit) cost	(0.4)	(0.4)	(0.3)
Amortization of net actuarial (gain) loss	(14.6)	(4.6)	2.0
Curtailment, settlement or special termination benefit (gain) loss	0.0	2.9	5.4
Expected participant contributions	(0.3)	(0.3)	(0.4)
Total other pension and postretirement (benefit) cost, net	(10.2)	(36.6)	(46.4)
Net periodic pension and OPEB (benefit) cost	$ (6.0)	$ (29.8)	$ (37.7)