Derivative Financial Instruments (Details 3) (USD $)	Oct. 31, 2013	Apr. 30, 2013
Outstanding derivative contracts
Gross contract notional amount	$ 750,000,000
Commodity contracts [Member]
Outstanding derivative contracts
Gross contract notional amount	324,500,000	347,600,000
Foreign currency exchange contracts [Member]
Outstanding derivative contracts
Gross contract notional amount	63,000,000	56,800,000
Interest rate contract [Member]
Outstanding derivative contracts
Gross contract notional amount	$ 750,000,000	$ 0