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, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments (a)	$ 31.4	[1]	$ 30.0	[1]	$ 30.3	[1],[2]
Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	40.2		30.4		59.4	[2]
Derivative financial instruments, liabilities	(297.9)		(54.1)		(10.7)	[2]
Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	18.7		12.8		0.4	[2]
Derivative financial instruments, liabilities			(0.1)		(7.2)	[2]
Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	0.1		0.1
Derivative financial instruments, liabilities	(17.0)		(21.0)		(29.2)	[2]
Cross-currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	4.3		2.1
Derivative financial instruments, liabilities					(2.1)	[2]
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments (a)	31.4	[1]	30.0	[1]	30.3	[1],[2]
Level 1 | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	14.1		10.6		9.8	[2]
Derivative financial instruments, liabilities	(69.4)		(21.2)		(6.1)	[2]
Level 1 | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	0		0		0	[2]
Derivative financial instruments, liabilities			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
Derivative financial instruments, liabilities	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
Derivative financial instruments, liabilities					0	[2]
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments (a)	0	[1]	0	[1]	0	[1],[2]
Level 2 | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	26.1		19.8		49.6	[2]
Derivative financial instruments, liabilities	(228.5)		(32.9)		(4.6)	[2]
Level 2 | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	18.7		12.8		0.4	[2]
Derivative financial instruments, liabilities			(0.1)		(7.2)	[2]
Level 2 | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	0.1		0.1
Derivative financial instruments, liabilities	(17.0)		(21.0)		(29.2)	[2]
Level 2 | Cross-currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	4.3		2.1
Derivative financial instruments, liabilities					(2.1)	[2]
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments (a)	0	[1]	0	[1]	0	[1],[2]
Level 3 | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets	0		0		0	[2]
Derivative financial instruments, liabilities	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	[2]
Derivative financial instruments, liabilities			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
Derivative financial instruments, liabilities	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
Derivative financial instruments, liabilities					$ 0	[2]

[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.