Annual report pursuant to Section 13 and 15(d)

Pension and Other Postretirement Benefit Programs - Amounts Recognized on the Consolidated Balance Sheets (Details)

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Pension and Other Postretirement Benefit Programs - Amounts Recognized on the Consolidated Balance Sheets (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]    
Pension benefit liabilities $ (5.7) $ (1.6)
Postretirement benefit liabilities (72.7) (75.5)
Retiree Health and Life Insurance Plans    
Defined Benefit Plan Disclosure [Line Items]    
Accounts payable and accrued expenses (6.7) (8.1)
Postretirement benefit liabilities (72.7) (75.5)
Net amount recognized (79.4) (83.6)
U.S. Pension Plan | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Prepaid pension costs 0.0 0.1
Pension benefit liabilities (5.0) (1.3)
Net amount recognized (5.0) (1.2)
Canadian Pension Plan | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Prepaid pension costs 0.0 0.1
Pension benefit liabilities (0.7) (0.3)
Net amount recognized $ (0.7) $ (0.2)