Retirement Benefits (Other Postretirement Benefit Plan Components) (Details) - Other Postretirement Benefits Plan - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1.1	$ 2.2	$ 2.8
Interest cost	1.6	2.0	2.2
Net actuarial loss amortization	0.2	0.7	0.8
Net periodic benefit cost	2.9	4.9	5.8
Discontinued Operations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	0.0	(0.4)	(0.7)
Continuing Operations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 2.9	$ 4.5	$ 5.1