Pension and Other Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 5	$ 5	$ 16	$ 15
Interest cost	8	9	23	26
Expected return on plan assets	(10)	(10)	(30)	(31)
Amortization of:
Prior service cost	0	0	1	1
Net actuarial loss	8	7	23	21
Net cost	11	11	33	32
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0	1	1
Interest cost	1	1	3	2
Amortization of:
Prior service cost	0	0	0	1
Net cost	$ 1	$ 1	$ 4	$ 4