Derivative Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Jul. 31, 2013	Apr. 30, 2013
[OtherCurrentAssetsMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Assets	$ 5.9	$ 6.4
[OtherCurrentAssetsMember] | [NondesignatedMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Assets	5.1	4.3
[OtherCurrentAssetsMember] | [CommodityContractMember] | [DesignatedAsHedgingInstrumentMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Assets	0.8	2.1
[OtherCurrentAssetsMember] | [CommodityContractMember] | [NondesignatedMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Assets	4.3	3.6
[OtherCurrentAssetsMember] | [ForeignExchangeContractMember] | [NondesignatedMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Assets	0.8	0.7
[OtherCurrentLiabilitiesMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Liabilities	4.1	4.5
[OtherCurrentLiabilitiesMember] | [NondesignatedMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Liabilities	2.8	2.5
[OtherCurrentLiabilitiesMember] | [CommodityContractMember] | [DesignatedAsHedgingInstrumentMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Liabilities	1.3	2.0
[OtherCurrentLiabilitiesMember] | [CommodityContractMember] | [NondesignatedMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Liabilities	2.5	2.3
[OtherCurrentLiabilitiesMember] | [ForeignExchangeContractMember] | [NondesignatedMember]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Liabilities	$ 0.3	$ 0.2