Derivative Financial Instruments (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Price Risk Derivatives [Abstract]
Net gains (losses) on mark-to-market valuation of unallocated derivative positions	$ (9.6)	$ (10.2)	$ (2.7)	$ (12.2)
Less: Net gains (losses) on derivative positions reclassified to segment operating profit	(19.3)	4.0	(25.0)	(5.7)
Unallocated derivative gains (losses)	$ 9.7	$ (14.2)	$ 22.3	$ (6.5)