Fair Value Measurements - Financial Assets and Liabilities that are Measured at Fair Value on a Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013	Jun. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	$ 13.7	$ 24.2	$ 18.7
Derivative financial instruments, liabilities	(43.1)	(55.4)	(80.7)
Fair Value, Measurements, Recurring | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	13.2	23.3	9.6
Derivative financial instruments, liabilities	(11.1)	(16.0)	(32.1)
Fair Value, Measurements, Recurring | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	0.5	0.9	1.0
Derivative financial instruments, liabilities	(4.8)	(7.2)	(1.7)
Fair Value, Measurements, Recurring | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets			8.1
Derivative financial instruments, liabilities	(25.2)	(31.0)	(46.9)
Fair Value, Measurements, Recurring | Cross currency swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, liabilities	(2.0)	(1.2)
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) | Fair Value, Measurements, Recurring | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	6.8	2.1	2.2
Derivative financial instruments, liabilities	(4.5)	(9.7)	(8.0)
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) | Fair Value, Measurements, Recurring | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	0	0	0
Derivative financial instruments, liabilities	0	0	0
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) | Fair Value, Measurements, Recurring | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets			0
Derivative financial instruments, liabilities	0	0	0
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) | Fair Value, Measurements, Recurring | Cross currency swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, liabilities	0	0
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	6.4	21.2	7.4
Derivative financial instruments, liabilities	(6.6)	(6.3)	(24.1)
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	0.5	0.9	1.0
Derivative financial instruments, liabilities	(4.8)	(7.2)	(1.7)
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets			8.1
Derivative financial instruments, liabilities	(25.2)	(31.0)	(46.9)
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Cross currency swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, liabilities	(2.0)	(1.2)
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	0	0	0
Derivative financial instruments, liabilities	0	0	0
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	0	0	0
Derivative financial instruments, liabilities	0	0	0
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets			0
Derivative financial instruments, liabilities	0	0	0
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Cross currency swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, liabilities	$ 0	$ 0