Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		6 Months Ended
		Oct. 31, 2016	Oct. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance		$ (148.4)	$ (109.8)
Reclassification adjustments		9.4	7.6
Current period (charge) credit		(7.0)	(25.0)
Income tax benefit (expense)		(10.1)	(1.6)
Accumulated Other Comprehensive Loss, Ending Balance		(156.1)	(128.8)
Foreign Currency Translation Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance		(13.1)	(2.3)
Reclassification adjustments		0.0	0.0
Current period (charge) credit		(26.2)	(22.9)
Income tax benefit (expense)		0.0	0.0
Accumulated Other Comprehensive Loss, Ending Balance		(39.3)	(25.2)
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]	(4.8)	(5.2)
Reclassification adjustments	[1]	0.3	0.3
Current period (charge) credit	[1]	0.0	0.0
Income tax benefit (expense)	[1]	(0.1)	(0.1)
Accumulated Other Comprehensive Loss, Ending Balance	[1]	(4.6)	(5.0)
Pension and Other Postretirement Liabilities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance	[2]	(134.1)	(105.6)
Reclassification adjustments	[2]	9.1	7.3
Current period (charge) credit	[2]	18.8	(1.5)
Income tax benefit (expense)	[2]	(9.9)	(1.7)
Accumulated Other Comprehensive Loss, Ending Balance	[2]	(116.1)	(101.5)
Unrealized Gain on Available-for-Sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Loss, Beginning Balance		3.6	3.3
Reclassification adjustments		0.0	0.0
Current period (charge) credit		0.4	(0.6)
Income tax benefit (expense)		(0.1)	0.2
Accumulated Other Comprehensive Loss, Ending Balance		$ 3.9	$ 2.9

[1] The reclassification from accumulated other comprehensive loss to interest expense was related to the termination of prior interest rate swaps.

[2] Amortization of net losses was reclassified from accumulated other comprehensive loss to selling, distribution, and administrative expenses.