Derivative Financial Instruments (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Price Risk Derivatives [Abstract]
Net gains (losses) on mark-to-market valuation of unallocated derivative positions	$ (2.4)	$ (9.6)	$ (28.6)	$ (2.7)
Less: Net gains (losses) on derivative positions reclassified to segment operating profit	(2.3)	(19.3)	(6.5)	(25.0)
Unallocated derivative gains (losses)	$ (0.1)	$ 9.7	$ (22.1)	$ 22.3