Fair Value Measurement - Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions		Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		$ 58.5	$ 45.4
Derivative financial liabilities		(179.9)	(75.2)
Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	[1]	30.3	30.0
Recurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	[1]	30.3	30.0
Recurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	[1]	0.0	0.0
Recurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	[1]	0.0	0.0
Recurring Basis | Commodity Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		29.0	30.4
Derivative financial liabilities		(169.0)	(54.1)
Recurring Basis | Commodity Contracts | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		17.4	10.6
Derivative financial liabilities		(70.0)	(21.2)
Recurring Basis | Commodity Contracts | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		11.6	19.8
Derivative financial liabilities		(99.0)	(32.9)
Recurring Basis | Commodity Contracts | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.0	0.0
Derivative financial liabilities		0.0	0.0
Recurring Basis | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		29.1	12.8
Derivative financial liabilities		(0.1)	(0.1)
Recurring Basis | Foreign Currency Contracts | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.0	0.0
Derivative financial liabilities		0.0	0.0
Recurring Basis | Foreign Currency Contracts | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		29.1	12.8
Derivative financial liabilities		(0.1)	(0.1)
Recurring Basis | Foreign Currency Contracts | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.0	0.0
Derivative financial liabilities		0.0	0.0
Recurring Basis | Cross-currency Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.4	2.1
Recurring Basis | Cross-currency Swaps | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.0	0.0
Recurring Basis | Cross-currency Swaps | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.4	2.1
Recurring Basis | Cross-currency Swaps | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.0	0.0
Recurring Basis | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.0	0.1
Derivative financial liabilities		(10.8)	(21.0)
Recurring Basis | Interest Rate Contracts | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.0	0.0
Derivative financial liabilities		0.0	0.0
Recurring Basis | Interest Rate Contracts | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.0	0.1
Derivative financial liabilities		(10.8)	(21.0)
Recurring Basis | Interest Rate Contracts | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets		0.0	0.0
Derivative financial liabilities		$ 0.0	$ 0.0

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