Retirement Benefits (Details 2) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	$ 5.3	$ 4.9
Net actuarial loss	921.9	1,235.1
Total	927.2	1,240.0
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(12.2)	(15.9)
Net actuarial loss	12.0	15.7
Total	$ (0.2)	$ (0.2)