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Retirement Benefits (Details 1) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]        
Termination benefits $ 17.4 $ 17.4    
Pension Benefits [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost - benefits earned during the year   12.7 $ 12.7 $ 16.4
Interest cost on benefits earned in prior years   86.3 105.5 104.8
Expected return on plan assets   (134.5) (131.3) (157.9)
Amortization of prior service cost (credit)   0.7 0.3 0.3
Amortization of net actuarial loss   74.5 73.7 65.9
Curtailment loss (gain)   0.0 0.0 0.4
Termination benefits   10.9 0.0 0.0
Total retirement benefit expense   50.6 60.9 29.9
Other Postretirement Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Service cost - benefits earned during the year   2.3 1.9 2.5
Interest cost on benefits earned in prior years   10.7 14.8 12.7
Expected return on plan assets   0.0 0.0 0.0
Amortization of prior service cost (credit)   (3.8) (2.9) (2.9)
Amortization of net actuarial loss   10.8 13.5 10.6
Curtailment loss (gain)   (0.2) 0.0 0.0
Termination benefits   6.7 0.0 0.0
Total retirement benefit expense   $ 26.5 $ 27.3 $ 22.9