Fair Value Measurements - Financial Assets and Liabilities that are Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions		Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	[1]	$ 31.8	$ 30.0	$ 30.4	[2]
Commodity Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		21.8	30.4	33.0	[2]
Derivative financial instruments, liabilities		(152.6)	(54.1)	(30.9)	[2]
Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		29.1	12.8	0.8	[2]
Derivative financial instruments, liabilities		(0.1)	(0.1)	(5.1)	[2]
Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		1.0	0.1
Derivative financial instruments, liabilities		(2.0)	(21.0)	(25.2)	[2]
Cross-Currency Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		8.2	2.1
Derivative financial instruments, liabilities	[2]			(2.0)
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	[1]	31.8	30.0	30.4	[2]
Level 1 | Commodity Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		13.6	10.6	17.9	[2]
Derivative financial instruments, liabilities		(58.6)	(21.2)	(15.6)	[2]
Level 1 | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		0.0	0.0	0.0	[2]
Derivative financial instruments, liabilities		0.0	0.0	0.0	[2]
Level 1 | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		0.0	0.0
Derivative financial instruments, liabilities		0.0	0.0	0.0	[2]
Level 1 | Cross-Currency Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		0.0	0.0
Derivative financial instruments, liabilities	[2]			0.0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	[1]	0.0	0.0	0.0	[2]
Level 2 | Commodity Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		8.2	19.8	15.1	[2]
Derivative financial instruments, liabilities		(94.0)	(32.9)	(15.3)	[2]
Level 2 | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		29.1	12.8	0.8	[2]
Derivative financial instruments, liabilities		(0.1)	(0.1)	(5.1)	[2]
Level 2 | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		1.0	0.1
Derivative financial instruments, liabilities		(2.0)	(21.0)	(25.2)	[2]
Level 2 | Cross-Currency Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		8.2	2.1
Derivative financial instruments, liabilities	[2]			(2.0)
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	[1]	0.0	0.0	0.0	[2]
Level 3 | Commodity Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		0.0	0.0	0.0	[2]
Derivative financial instruments, liabilities		0.0	0.0	0.0	[2]
Level 3 | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		0.0	0.0	0.0	[2]
Derivative financial instruments, liabilities		0.0	0.0	0.0	[2]
Level 3 | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		0.0	0.0
Derivative financial instruments, liabilities		0.0	0.0	0.0	[2]
Level 3 | Cross-Currency Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		$ 0.0	$ 0.0
Derivative financial instruments, liabilities	[2]			$ 0.0

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

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