Derivative Financial Instruments (Details 3) (USD $)	Jan. 31, 2014	Apr. 30, 2013
Outstanding derivative contracts
Gross contract notional amount	$ 750,000,000
Commodity contracts [Member]
Outstanding derivative contracts
Gross contract notional amount	369,000,000	347,600,000
Foreign currency exchange contracts [Member]
Outstanding derivative contracts
Gross contract notional amount	95,100,000	56,800,000
Interest rate contract [Member]
Outstanding derivative contracts
Gross contract notional amount	$ 750,000,000	$ 0