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Retirement Plans (Pension and Other Postretirement Benefits Activity in Accumulated Other Comprehensive Income) (Details) - 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]      
Balance at beginning of year $ 47.0 $ 57.7  
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement 0.0 16.6 $ 0.5
Other 2.4 0.1  
Pension Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Balance at beginning of year 93.4 110.8  
Balance at beginning of year 110.8    
Actuarial loss (13.5)    
Balance at end of year 93.4 $ 110.8  
Prior year actuarial loss amortization to net periodic cost $ (4.0)