Annual report pursuant to Section 13 and 15(d)

Pension and Other Postretirement Benefit Programs - Fair Value Measurement (Details)

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Pension and Other Postretirement Benefit Programs - Fair Value Measurement (Details) - Pension Plan - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
U.S. Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets $ 390.8 $ 363.2 $ 0.0
U.S. Pension Plan | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets (0.5) 0.0  
U.S. Pension Plan | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 391.3 363.2  
U.S. Pension Plan | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
U.S. Pension Plan | Fixed income securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 219.2 219.1  
U.S. Pension Plan | Fixed income securities | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
U.S. Pension Plan | Fixed income securities | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 219.2 219.1  
U.S. Pension Plan | Fixed income securities | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
U.S. Pension Plan | Equities      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 172.1 144.1  
U.S. Pension Plan | Equities | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
U.S. Pension Plan | Equities | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 172.1 144.1  
U.S. Pension Plan | Equities | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
U.S. Pension Plan | Other      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets (0.5)    
U.S. Pension Plan | Other | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets (0.5)    
U.S. Pension Plan | Other | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0    
U.S. Pension Plan | Other | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0    
Canadian Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 17.1 16.5 $ 0.0
Canadian Pension Plan | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.4 0.5  
Canadian Pension Plan | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 16.7 16.0  
Canadian Pension Plan | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Canadian Pension Plan | Fixed income securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 8.4 8.1  
Canadian Pension Plan | Fixed income securities | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Canadian Pension Plan | Fixed income securities | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 8.4 8.1  
Canadian Pension Plan | Fixed income securities | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Canadian Pension Plan | Equities      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 8.3 7.9  
Canadian Pension Plan | Equities | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Canadian Pension Plan | Equities | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 8.3 7.9  
Canadian Pension Plan | Equities | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Canadian Pension Plan | Other      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.4 0.5  
Canadian Pension Plan | Other | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.4 0.5  
Canadian Pension Plan | Other | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Canadian Pension Plan | Other | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets $ 0.0 $ 0.0