Employee Retirement Plans and Postretirement Benefits Net Periodic Pension (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Total other non-service pension and postretirement benefits (costs), net		$ (30.3)	$ (2.9)	$ (38.2)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		6.0	7.0	9.3
Interest cost		18.8	25.5	25.8
Expected return on plan assets		0.2	0.5	0.5
Amortization of prior service cost (benefit)		(0.7)	(0.7)	(0.2)
Amortization of net actuarial loss (gain)		(14.5)	(14.1)	(1.7)
Curtailment, settlement or special termination benefit loss (gain)		0.0	0.0	0.1
Expected Participant Contributions		0.0	0.0	0.0
Total other non-service pension and postretirement benefits (costs), net		3.8	11.2	24.5
Net periodic pension cost (benefit)		9.8	18.2	33.8
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		2.7	4.0	5.5
Interest cost		120.5	161.9	161.8
Expected return on plan assets		(161.8)	(217.3)	(232.8)
Amortization of prior service cost (benefit)		0.3	1.1	0.7
Amortization of net actuarial loss (gain)		7.3	10.4	7.6
Curtailment, settlement or special termination benefit loss (gain)		0.0	30.5	0.8
Expected Participant Contributions		(0.4)	(0.7)	(0.8)
Total other non-service pension and postretirement benefits (costs), net		(34.1)	(14.1)	(62.7)
Net periodic pension cost (benefit)		(31.4)	(10.1)	(57.2)
Pension Plan [Member] | Canada
Defined Benefit Plan Disclosure [Line Items]
Curtailment, settlement or special termination benefit loss (gain)	$ 29.8
defined benefit plans and other postretirement benefit plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		8.7	11.0	14.8
Interest cost		139.3	187.4	187.6
Expected return on plan assets		(161.6)	(216.8)	(232.3)
Amortization of prior service cost (benefit)		(0.4)	0.4	0.5
Amortization of net actuarial loss (gain)		(7.2)	(3.7)	5.9
Curtailment, settlement or special termination benefit loss (gain)		0.0	30.5	0.9
Expected Participant Contributions		(0.4)	(0.7)	(0.8)
Total other non-service pension and postretirement benefits (costs), net		(30.3)	(2.9)	(38.2)
Net periodic pension cost (benefit)		$ (21.6)	$ 8.1	$ (23.4)