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) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets $ 337.1    
Pension Plan | U.S. Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 337.1 $ 390.8 $ 363.2
Pension Plan | U.S. Pension Plan | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets   (0.5)  
Pension Plan | U.S. Pension Plan | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets   391.3  
Pension Plan | U.S. Pension Plan | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets   0.0  
Pension Plan | U.S. Pension Plan | Fixed income securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 202.4 219.2  
Pension Plan | U.S. Pension Plan | Fixed income securities | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | U.S. Pension Plan | Fixed income securities | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 202.4 219.2  
Pension Plan | U.S. Pension Plan | Fixed income securities | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | U.S. Pension Plan | Equities      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 143.2 172.1  
Pension Plan | U.S. Pension Plan | Equities | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | U.S. Pension Plan | Equities | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 143.2 172.1  
Pension Plan | U.S. Pension Plan | Equities | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | U.S. Pension Plan | Other      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets (0.4) (0.5)  
Pension Plan | U.S. Pension Plan | Other | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets (0.4) (0.5)  
Pension Plan | U.S. Pension Plan | Other | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | U.S. Pension Plan | Other | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | U.S. Pension Plan | Plan Assets Before Transfer to AHF, LLC      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 345.2    
Pension Plan | U.S. Pension Plan | Plan Assets Before Transfer to AHF, LLC | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets (0.4)    
Pension Plan | U.S. Pension Plan | Plan Assets Before Transfer to AHF, LLC | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 345.6    
Pension Plan | U.S. Pension Plan | Plan Assets Before Transfer to AHF, LLC | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0    
Pension Plan | U.S. Pension Plan | Assets to be Transferred to AHF      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets (8.1)    
Pension Plan | Canadian Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 13.6 17.1 $ 16.5
Pension Plan | Canadian Pension Plan | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.2 0.4  
Pension Plan | Canadian Pension Plan | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 13.4 16.7  
Pension Plan | Canadian Pension Plan | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | Canadian Pension Plan | Fixed income securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 6.9 8.4  
Pension Plan | Canadian Pension Plan | Fixed income securities | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | Canadian Pension Plan | Fixed income securities | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 6.9 8.4  
Pension Plan | Canadian Pension Plan | Fixed income securities | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | Canadian Pension Plan | Equities      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 6.5 8.3  
Pension Plan | Canadian Pension Plan | Equities | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | Canadian Pension Plan | Equities | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 6.5 8.3  
Pension Plan | Canadian Pension Plan | Equities | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | Canadian Pension Plan | Other      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.2 0.4  
Pension Plan | Canadian Pension Plan | Other | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.2 0.4  
Pension Plan | Canadian Pension Plan | Other | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets 0.0 0.0  
Pension Plan | Canadian Pension Plan | Other | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair Value of Plan Assets $ 0.0 $ 0.0