Derivative Financial Instruments (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013	Apr. 30, 2013
Derivative Financial Instruments (Additional Textual) [Abstract]
Cash margin accounts related to derivative instruments recognized	$ 6.7		$ 6.7		$ 5.5
Interest rate contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain recognized on derivative instrument	13.7		13.7
3.50% Senior Notes due October 15, 2021 [Member]
Debt Instrument [Line Items]
Interest rate on notes	3.50%		3.50%		3.50%
Commodity contracts [Member]
Derivative Financial Instruments (Textual) [Abstract]
Derivative instrument maturity			1 year
Deferred pre-tax loss included in accumulated other comprehensive loss					(12.2)
Tax impact related to deferred losses and gains on cash flow hedges included in accumulated other comprehensive loss					4.4
Maximum expected recognized period of deferred loss in earnings			1 year
Losses reclassified from other comprehensive income to interest expense	5.7	12.0	18.4	31.0
Interest rate contract [Member]
Derivative Financial Instruments (Textual) [Abstract]
Deferred pre-tax loss included in accumulated other comprehensive loss	(5.0)		(5.0)		(5.4)
Tax impact related to deferred losses and gains on cash flow hedges included in accumulated other comprehensive loss	1.8		1.8		1.9
Expected period for recognition of the hedge loss reclassified to interest expense			12 months
Losses reclassified from other comprehensive income to interest expense	$ 0.1	$ 0.1	$ 0.4	$ 0.4
Foreign currency exchange contracts [Member]
Derivative Financial Instruments (Textual) [Abstract]
Derivative instrument maturity			1 year