Pension and Other Postretirement Benefits (Funded Status Recorded on Accompanying Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2014	Apr. 30, 2013
Funded status is recorded on the accompanying consolidated balance sheets
Accounts payable and accrued expenses	$ (7)	$ (6)
Accrued postretirement benefits	(244)	(280)
Pension Benefits [Member]
Funded status is recorded on the accompanying consolidated balance sheets
Other assets	2	2
Accounts payable and accrued expenses	(4)	(3)
Accrued postretirement benefits	(178)	(209)
Net liability	(180)	(210)
Accumulated other comprehensive income (loss), before tax:
Net actuarial gain (loss)	(296)	(336)
Prior service credit (cost)	(5)	(7)
Total	(301)	(343)
Medical and Life Insurance Benefits [Member]
Funded status is recorded on the accompanying consolidated balance sheets
Other assets	0	0
Accounts payable and accrued expenses	(3)	(3)
Accrued postretirement benefits	(66)	(71)
Net liability	(69)	(74)
Accumulated other comprehensive income (loss), before tax:
Net actuarial gain (loss)	(14)	(11)
Prior service credit (cost)	5	(5)
Total	$ (9)	$ (16)