Derivative Instruments and Fair Value Measurement (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Sep. 30, 2012
Assets and liabilities measured at fair value on a recurring basis
Net derivative asset / (liability) designated as hedging instruments	$ 6.8	$ 0.1
Net derivative asset / (liability) not designated as hedging instruments	(4.9)	(10.7)
Other current assets [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivatives assets designated as hedging instruments	9.7	8.7
Derivatives assets not designated as hedging instruments	1.9	2.3
Other assets [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivatives assets designated as hedging instruments	1.1	1.3
Derivatives assets not designated as hedging instruments	0	0.1
Other current liabilities [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivatives liabilities designated as hedging instruments	(3.0)	(8.4)
Derivatives liabilities not designated as hedging instruments	(5.6)	(13.1)
Other liabilities [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivatives liabilities designated as hedging instruments	(1.0)	(1.5)
Derivatives liabilities not designated as hedging instruments	$ (1.2)	$ 0