Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Jul. 31, 2015	Jul. 31, 2014
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 6	$ 5
Interest cost	9	8
Expected return on plan assets	(10)	(10)
Amortization of:
Net actuarial loss	7	6
Net cost	12	9
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	1	1
Amortization of:
Net cost	$ 1	$ 1