Fair Value Measurement - Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	$ 45.4		$ 26.3	[1]
Derivative financial liabilities	75.2		57.5	[1]
Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	30.0	[2]	27.1	[2]
Recurring Basis | Commodity Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	30.4		25.4	[1]
Derivative financial liabilities	(54.1)		(18.1)	[1]
Recurring Basis | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	12.8		0.9	[1]
Derivative financial liabilities	(0.1)		(7.2)	[1]
Recurring Basis | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0.1
Derivative financial liabilities	(21.0)		(31.0)	[1]
Recurring Basis | Cross-currency Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	2.1
Derivative financial liabilities			(1.2)	[1]
Level 1 | Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	30.0	[2]	27.1	[2]
Level 1 | Recurring Basis | Commodity Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	10.6		2.6	[1]
Derivative financial liabilities	(21.2)		(8.8)	[1]
Level 1 | Recurring Basis | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0	[1]
Derivative financial liabilities	0		0	[1]
Level 1 | Recurring Basis | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0
Derivative financial liabilities	0		0	[1]
Level 1 | Recurring Basis | Cross-currency Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0
Derivative financial liabilities			0	[1]
Level 2 | Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	0	[2]	0	[2]
Level 2 | Recurring Basis | Commodity Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	19.8		22.8	[1]
Derivative financial liabilities	(32.9)		(9.3)	[1]
Level 2 | Recurring Basis | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	12.8		0.9	[1]
Derivative financial liabilities	(0.1)		(7.2)	[1]
Level 2 | Recurring Basis | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0.1
Derivative financial liabilities	(21.0)		(31.0)	[1]
Level 2 | Recurring Basis | Cross-currency Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	2.1
Derivative financial liabilities			(1.2)	[1]
Level 3 | Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	0	[2]	0	[2]
Level 3 | Recurring Basis | Commodity Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0	[1]
Derivative financial liabilities	0		0	[1]
Level 3 | Recurring Basis | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0	[1]
Derivative financial liabilities	0		0	[1]
Level 3 | Recurring Basis | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0
Derivative financial liabilities	0		0	[1]
Level 3 | Recurring Basis | Cross-currency Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0
Derivative financial liabilities			$ 0	[1]

[1] Certain immaterial amounts have been revised to correct the classification of derivatives.

[2] Consists primarily of mutual fund investments held in grantor trusts associated with non-qualified supplemental retirement plans (see Note 8).