Pension and Other Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 5	$ 5
Interest cost	8	9
Expected return on plan assets	(10)	(10)
Amortization of:
Net actuarial loss	8	7
Net cost	11	11
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1	0
Interest cost	1	1
Amortization of:
Net cost	$ 2	$ 1