Pension and Other Postretirement Benefits (Funded Status Recorded on Accompanying Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Funded status is recorded on the accompanying consolidated balance sheets
Accounts payable and accrued expenses	$ (6)	$ (6)
Accrued postretirement benefits	(280)	(278)
Pension Benefits [Member]
Funded status is recorded on the accompanying consolidated balance sheets
Other assets	2	3
Accounts payable and accrued expenses	(3)	(3)
Accrued postretirement benefits	(209)	(219)
Net liability	(210)	(219)
Accumulated other comprehensive loss:
Net actuarial loss (gain)	336	346
Prior service cost	7	4
Total	343	350
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	(71)	(59)
Net liability	(74)	(62)
Accumulated other comprehensive loss:
Net actuarial loss (gain)	11	1
Prior service cost	5	6
Total	$ 16	$ 7