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Income Taxes - Summary of Changes to Unrecognized Tax Benefits Reserves Excluding Related Interest and Penalties (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2011
Income Tax Disclosure [Abstract]      
Unrecognized Tax Benefits that Would Impact Effective Tax Rate $ 10.1    
Unrecognized Tax Benefits that Would Result in Deferred Tax Assets 3.7    
Accrued interest and penalties related to the uncertain tax positions 3.7 3.6  
Increase Decrease Interest And Penalties 0 (1.2) (1.4)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]      
Unrecognized tax benefits 5.9 9.0 13.2
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions 9.1 0.7 1.6
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions (0.3) (1.3) (0.8)
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions 0.5 0.8 0.6
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities (0.1) (1.7) (1.9)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations (1.3) (1.6) (3.7)
Unrecognized tax benefits $ 13.8 $ 5.9 $ 9.0