Annual report pursuant to Section 13 and 15(d)

Pension And Other Postretirement Benefit Programs - Amounts Recognized in AOCI (Details)

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Pension And Other Postretirement Benefit Programs - Amounts Recognized in AOCI (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Retiree Health and Life Insurance Plans    
Defined Benefit Plan Disclosure [Line Items]    
Net actuarial gain (loss) $ 25.6 $ 30.5
United States | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Net actuarial gain (loss) (106.7) (123.1)
Canadian Pension Plan | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Net actuarial gain (loss) $ (4.9) $ (4.8)