Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Jul. 31, 2016	Jul. 31, 2015
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 6	$ 6
Interest cost	9	9
Expected return on plan assets	(10)	(10)
Amortization of:
Net actuarial loss	6	7
Net cost	11	12
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	1	1
Amortization of:
Prior service cost	(1)	0
Net cost	$ 0	$ 1