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 ($)
Dec. 31, 2020
Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]    
Pension benefit liabilities $ (4,600,000) $ (16,000,000.0)
Postretirement benefit liabilities (55,600,000) (59,700,000)
Retiree Health and Life Insurance Plans    
Defined Benefit Plan Disclosure [Line Items]    
Accounts payable and accrued expenses (4,000,000.0) (5,600,000)
Postretirement benefit liabilities (55,600,000) (59,700,000)
Net amount recognized (59,600,000) (65,300,000)
United States | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Prepaid Expense, Noncurrent 1,100,000  
Pension benefit liabilities (2,300,000) (13,900,000)
Accounts payable and accrued expenses   (11,800,000)
Net amount recognized (1,200,000) (13,900,000)
Canadian Pension Plan | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Pension benefit liabilities (2,300,000) (2,100,000)
Net amount recognized $ (2,300,000) $ (2,100,000)