Derivative Instruments and Fair Value Measurement (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Sep. 30, 2011
Assets and liabilities measured at fair value on a recurring basis
Net derivative asset / (liability) designated as hedging instruments	$ (3.0)	$ 10.2
Net derivative asset / (liability) not designated as hedging instruments	(4.6)	11.7
Other current assets [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivatives assets designated as hedging instruments	8.9	15.9
Derivatives assets not designated as hedging instruments	0.9	12.1
Other assets [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivatives assets designated as hedging instruments	0.8	1.6
Other current liabilities [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivatives liabilities designated as hedging instruments	(11.1)	(5.9)
Derivatives liabilities not designated as hedging instruments	(5.5)	(0.4)
Other liabilities [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivatives liabilities designated as hedging instruments	$ (1.6)	$ (1.4)