Pension and Other Postretirement Benefits (Funded Status Recorded on Accompanying Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2015	Apr. 30, 2014
Funded status is recorded on the accompanying consolidated balance sheets
Accounts payable and accrued expenses	$ (7)	$ (7)
Accrued postretirement benefits	(311)	(244)
Pension Benefits [Member]
Funded status is recorded on the accompanying consolidated balance sheets
Other assets	0	2
Accounts payable and accrued expenses	(4)	(4)
Accrued postretirement benefits	(257)	(178)
Net liability	(261)	(180)
Accumulated other comprehensive income (loss), before tax:
Net actuarial gain (loss)	(353)	(296)
Prior service credit (cost)	(4)	(5)
Total	(357)	(301)
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	(54)	(66)
Net liability	(57)	(69)
Accumulated other comprehensive income (loss), before tax:
Net actuarial gain (loss)	(16)	(14)
Prior service credit (cost)	18	5
Total	$ 2	$ (9)