Derivative Financial Instruments (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended				12 Months Ended
	Jan. 31, 2015		Jan. 31, 2014		Jan. 31, 2015		Jan. 31, 2014		Apr. 30, 2014
Derivative Financial Instruments (Textual) [Abstract]
Interest receivable	$ 4.6				$ 4.6
Derivative Financial Instruments (Additional Textual) [Abstract]
Cash margin accounts related to derivative instruments recognized	20.3				20.3				8.1
Cumulative realized net mark-to-market valuation of certain derivative positions recognized in unallocated derivative gains (losses)					8.5
Net mark-to-market valuation of certain derivative positions recognized in unallocated derivative gains (losses)	13.4	[1]	4.0	[1]	(0.4)	[1]	7.1	[1]	4.1
Cumulative net mark-to-market valuation of certain derivative positions recognized in unallocated derivative gains (losses)					3.7
Net gains (losses) on mark-to-market valuation of unallocated derivative positions	(2.2)		3.8		(20.2)		2.6
3.50% Senior Notes due October 15, 2021 [Member]
Debt Instrument [Line Items]
Interest rate on notes	3.50%				3.50%				3.50%
Foreign currency exchange contracts [Member]
Derivative Financial Instruments (Textual) [Abstract]
Derivative instrument maturity					1 year
Derivative Financial Instruments (Additional Textual) [Abstract]
Net gains (losses) on mark-to-market valuation of unallocated derivative positions	11.7		2.9		14.1		4.8
Interest rate contract [Member]
Derivative Financial Instruments (Textual) [Abstract]
Deferred pre-tax gain (loss) included in accumulated other comprehensive loss	(4.4)				(4.4)				(4.8)
Tax impact related to deferred losses and gains on cash flow hedges included in accumulated other comprehensive loss	1.6				1.6				1.7
Effective portion of the hedge loss reclassified to interest expense over the next twelve months					0.6
Expected period for recognition of the hedge loss reclassified to interest expense					12 months
Gain on early termination agreement					58.1
Interest receivable	4.6				4.6
Commodity contracts [Member]
Derivative Financial Instruments (Textual) [Abstract]
Deferred net gains (losses) recognized in accumulated other comprehensive loss	0.4				0.4				18.3
Derivative instrument maturity					1 year
Deferred pre-tax gain (loss) included in accumulated other comprehensive loss	0.7				0.7				29.1
Tax impact related to deferred losses and gains on cash flow hedges included in accumulated other comprehensive loss	(0.3)				(0.3)				(10.8)
Maximum expected recognized period of deferred loss in earnings	1 year
Derivative Financial Instruments (Additional Textual) [Abstract]
Net gains (losses) on mark-to-market valuation of unallocated derivative positions	(13.9)		0.9		(34.3)		(2.2)
2015 [Member]
Derivative Financial Instruments (Textual) [Abstract]
Amortization of deferred gain on early termination agreement	2.2
2016 [Member]
Derivative Financial Instruments (Textual) [Abstract]
Amortization of deferred gain on early termination agreement	7.4
2017 [Member]
Derivative Financial Instruments (Textual) [Abstract]
Amortization of deferred gain on early termination agreement	7.6
2018 [Member]
Derivative Financial Instruments (Textual) [Abstract]
Amortization of deferred gain on early termination agreement	7.8
2019 [Member]
Derivative Financial Instruments (Textual) [Abstract]
Amortization of deferred gain on early termination agreement	8.0
2020 [Member]
Derivative Financial Instruments (Textual) [Abstract]
Amortization of deferred gain on early termination agreement	8.1
2021 [Member]
Derivative Financial Instruments (Textual) [Abstract]
Amortization of deferred gain on early termination agreement	8.4
2022 [Member]
Derivative Financial Instruments (Textual) [Abstract]
Amortization of deferred gain on early termination agreement	$ 4.0

[1] As of January 31, 2015, the cumulative amount of net derivative gains from economic hedges that has not yet been allocated to segment profit was $3.7, including net gains of $4.1 incurred prior to 2015. For additional information, see Note 12: Derivative Financial Instruments.