Pensions and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Oct. 31, 2016	Jul. 31, 2016	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015
Components of net periodic benefit cost
Plan amendment change in AOCI		$ (25.2)
Defined Benefit Pension Plans [Member]
Components of net periodic benefit cost
Service cost	$ 3.6		$ 4.4	$ 7.7	$ 9.1
Interest cost	6.2		6.9	12.9	13.9
Expected return on plan assets	(7.3)		(8.3)	(14.6)	(16.7)
Recognized net actuarial loss (gain)	3.4		2.7	7.1	5.4
Prior service cost (credit)	0.3		0.2	0.6	0.4
Curtailment gain	0.0		(0.8)	0.0	(4.5)
Settlement Loss				0.1	0.0
Net periodic benefit cost	6.2		5.1	13.8	7.6
Other Postretirement Benefits [Member]
Components of net periodic benefit cost
Service cost	0.6		0.5	1.2	1.1
Interest cost	0.6		0.7	1.3	1.4
Expected return on plan assets	0.0		0.0	0.0	0.0
Recognized net actuarial loss (gain)	(0.1)		(0.1)	(0.1)	(0.1)
Prior service cost (credit)	(0.3)		(0.2)	(0.7)	(0.5)
Curtailment gain	0.0		(0.1)	0.0	(0.1)
Settlement Loss				0.0	0.0
Net periodic benefit cost	$ 0.8		$ 0.8	$ 1.7	$ 1.8