Fair Value Measurements - Financial Assets and Liabilities that are Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions		Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		$ 48.6		$ 67.8
Derivative financial instruments, liabilities		(117.1)		(180.8)
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	[1]	31.8	$ 30.3	31.8
Fair Value, Measurements, Recurring | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		37.0	29.0	22.2
Derivative financial instruments, liabilities		(107.4)	(169.0)	(168.3)
Fair Value, Measurements, Recurring | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		11.6	29.1	35.8
Derivative financial instruments, liabilities		(5.0)	(0.1)
Fair Value, Measurements, Recurring | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets				0.1
Derivative financial instruments, liabilities		(3.4)	(10.8)	(12.5)
Fair Value, Measurements, Recurring | Cross-currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets			0.4	9.7
Derivative financial instruments, liabilities		(1.3)
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	[1]	31.8	30.3	31.8
Fair Value, Measurements, Recurring | Level 1 | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		20.3	17.4	13.9
Derivative financial instruments, liabilities		(59.0)	(70.0)	(64.0)
Fair Value, Measurements, Recurring | 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
Derivative financial instruments, liabilities		0.0	0.0
Fair Value, Measurements, Recurring | 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	0.0	0.0
Fair Value, Measurements, Recurring | 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		0.0
Fair Value, Measurements, Recurring | 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
Fair Value, Measurements, Recurring | Level 2 | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		16.7	11.6	8.3
Derivative financial instruments, liabilities		(48.4)	(99.0)	(104.3)
Fair Value, Measurements, Recurring | Level 2 | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets		11.6	29.1	35.8
Derivative financial instruments, liabilities		(5.0)	(0.1)
Fair Value, Measurements, Recurring | Level 2 | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets				0.1
Derivative financial instruments, liabilities		(3.4)	(10.8)	(12.5)
Fair Value, Measurements, Recurring | Level 2 | Cross-currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative financial instruments, assets			0.4	9.7
Derivative financial instruments, liabilities		(1.3)
Fair Value, Measurements, Recurring | 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
Fair Value, Measurements, Recurring | 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
Derivative financial instruments, liabilities		0.0	0.0	0.0
Fair Value, Measurements, Recurring | 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
Derivative financial instruments, liabilities		0.0	0.0
Fair Value, Measurements, Recurring | 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	0.0	0.0
Fair Value, Measurements, Recurring | 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		$ 0.0

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