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Employee Benefit Plans - Pre-tax Amounts Recorded in AOCI (Details) - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Pension Plan [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net actuarial gain (loss) $ (225.4) $ (278.0)
Net prior service credit (cost) (1.6) (1.8)
Total amounts recorded (227.0) (279.8)
Other Postretirement Benefits Plan [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net actuarial gain (loss) 31.3 (4.9)
Net prior service credit (cost) 1.6 3.1
Total amounts recorded $ 32.9 $ (1.8)