Annual report pursuant to Section 13 and 15(d)

Pension and Other Postretirement Benefit Programs - Schedule of Change in Benefit Obligation and Change in Plan Assets (Details)

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Pension and Other Postretirement Benefit Programs - Schedule of Change in Benefit Obligation and Change in Plan Assets (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Canadian Pension Plan      
Change in plan assets:      
Accumulated benefit obligation $ 17.8 $ 16.7  
Retiree Health and Life Insurance Plans      
Change in benefit obligation:      
Benefit obligations as of beginning of period 83.6 3.5  
Liabilities assumed from Separation 0.0 82.9  
Service cost 0.4 0.1 $ 0.0
Interest cost 3.3 2.7 0.1
Plan participants' contributions 1.7 1.6  
Actuarial (gain) loss 0.2 1.1  
Benefits paid (9.8) (8.3)  
Benefit obligation as of end of period 79.4 83.6 3.5
Change in plan assets:      
Fair value of plan assets as of beginning of period 0.0 0.0  
Employer contribution 8.1 6.7  
Benefits paid (9.8) (8.3)  
Fair value of plan assets as of end of period 0.0 0.0 0.0
Funded status of the plans (79.4) (83.6)  
U.S. Pension Plan      
Change in plan assets:      
Accumulated benefit obligation 394.5 362.2  
U.S. Pension Plan      
Change in plan assets:      
Employer contribution 0.1 0.0  
U.S. Pension Plan | Pension Plan      
Change in benefit obligation:      
Benefit obligations as of beginning of period 364.4 0.0  
Liabilities assumed from Separation 0.0 365.2  
Service cost 5.4 4.3 0.0
Interest cost 15.4 11.7 0.0
Foreign currency translation adjustment 0.0 0.0  
Actuarial (gain) loss 28.4 (6.2)  
Benefits paid (17.8) (10.6)  
Benefit obligation as of end of period 395.8 364.4 0.0
Change in plan assets:      
Fair value of plan assets as of beginning of period 363.2 0.0  
Assets received from separation 0.0 362.2  
Actual return on plan assets 45.3 11.6  
Foreign currency translation adjustment 0.0 0.0  
Benefits paid (17.8) (10.6)  
Fair value of plan assets as of end of period 390.8 363.2 0.0
Funded status of the plans (5.0) (1.2)  
Canadian Pension Plan      
Change in plan assets:      
Employer contribution 0.0 0.0  
Canadian Pension Plan | Pension Plan      
Change in benefit obligation:      
Benefit obligations as of beginning of period 16.7 0.0  
Liabilities assumed from Separation 0.0 20.2  
Service cost 0.0 0.0  
Interest cost 0.6 0.5 0.0
Foreign currency translation adjustment 1.2 (0.8)  
Actuarial (gain) loss 1.1 (0.5)  
Benefits paid (1.8) (2.7)  
Benefit obligation as of end of period 17.8 16.7 0.0
Change in plan assets:      
Fair value of plan assets as of beginning of period 16.5 0.0  
Assets received from separation 0.0 19.2  
Actual return on plan assets 1.2 0.8  
Foreign currency translation adjustment 1.2 (0.8)  
Benefits paid (1.8) (2.7)  
Fair value of plan assets as of end of period 17.1 16.5 $ 0.0
Funded status of the plans $ (0.7) $ (0.2)