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Retirement Benefits (Details1) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Pension Plans Defined Benefit        
Defined Benefit Plan Disclosure [Line Items]        
Service cost - benefits earned during the year $ 3.5 $ 5.1 $ 7.0 $ 10.3
Interest cost on benefits earned in prior years 29.2 31.3 58.4 62.7
Expected return on plan assets (36.7) (37.1) (73.4) (74.3)
Amortization of prior service cost (credit) 0.3 0.3 0.6 0.6
Amortization of net actuarial loss 15.7 16.4 31.3 32.7
Total retirement benefit expense 12.0 16.0 23.9 32.0
Other Postretirement Benefit Plan, Defined Benefit        
Defined Benefit Plan Disclosure [Line Items]        
Service cost - benefits earned during the year 0.6 0.7 1.2 1.3
Interest cost on benefits earned in prior years 3.6 3.9 7.3 8.0
Expected return on plan assets 0.0 0.0 0.0 0.0
Amortization of prior service cost (credit) (0.7) (0.8) (1.4) (0.2)
Amortization of net actuarial loss 2.3 2.4 4.5 4.8
Total retirement benefit expense $ 5.8 $ 6.2 $ 11.6 $ 13.9