Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016		Jan. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance				$ (109.8)		$ (51.6)
Reclassification adjustments				10.9		(17.4)
Current period (charge) credit				(43.1)		(46.5)
Income tax benefit (expense)				(4.8)		6.0
Accumulated Other Comprehensive Loss, Ending Balance		$ (146.8)	$ (109.5)	(146.8)		(109.5)
Cost of Products Sold [Member] | Commodity contracts [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reclassified from accumulated other comprehensive loss to earnings (effective portion)		0.0	9.6	0.0		28.4
Interest Expense [Member] | Interest rate contract [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reclassified from accumulated other comprehensive loss to earnings (effective portion)		(0.1)	(0.1)	(0.4)		(0.4)
Foreign Currency Translation Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance				(2.3)		31.7
Reclassification adjustments				0.0		0.0
Current period (charge) credit				(44.4)		(49.6)
Income tax benefit (expense)				0.0		0.0
Accumulated Other Comprehensive Loss, Ending Balance		(46.7)	(17.9)	(46.7)		(17.9)
Unrealized (Loss) Gain on Cash Flow Hedging Derivatives [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance	[1]			(5.2)		15.3
Reclassification adjustments	[1]			0.4		(28.0)
Current period (charge) credit	[1]			0.0		0.0
Income tax benefit (expense)	[1]			(0.1)		10.4
Accumulated Other Comprehensive Loss, Ending Balance	[1]	(4.9)	(2.3)	(4.9)		(2.3)
Pension and Other Postretirement Liabilities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance	[2]			(105.6)		(102.0)
Reclassification adjustments		(3.2)	(6.6)	10.5	[2]	10.6	[2]
Current period (charge) credit	[2]			1.3		1.7
Income tax benefit (expense)	[2]			(4.7)		(3.9)
Accumulated Other Comprehensive Loss, Ending Balance	[2]	(98.5)	(93.6)	(98.5)		(93.6)
Unrealized Gain on Available-for-Sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance				3.3		3.4
Reclassification adjustments				0.0		0.0
Current period (charge) credit				0.0		1.4
Income tax benefit (expense)				0.0		(0.5)
Accumulated Other Comprehensive Loss, Ending Balance		$ 3.3	$ 4.3	$ 3.3		$ 4.3

[1] Of the total losses reclassified from accumulated other comprehensive loss, $0.1 of expense was reclassified to interest expense related to the terminated interest rate swap for both the three months ended January 31, 2016 and 2015, and $0.4 of expense was reclassified for both the nine months ended January 31, 2016 and 2015. Of the total gains and losses reclassified from accumulated other comprehensive loss, $9.6 and $28.4 of income was reclassified to cost of products sold related to commodity derivatives for the three and nine months ended January 31, 2015, respectively.

[2] Of the total amortization of net losses reclassified from accumulated other comprehensive loss to selling, distribution, and administrative expense for the nine months ended January 31, 2016 and 2015, $3.2 and $6.6 was reclassified for the three months ended January 31, 2016 and 2015, respectively.