Pension and Other Postretirement Benefits (Funded Status Recorded on Accompanying Balance Sheets) (Details) - USD ($) $ in Millions	Apr. 30, 2021	Apr. 30, 2020
Funded status is recorded on the accompanying consolidated balance sheets
Accrued postretirement benefits	$ (219)	$ (297)
Pension Benefits [Member]
Funded status is recorded on the accompanying consolidated balance sheets
Other assets	4	0
Accounts payable and accrued expenses	(7)	(7)
Accrued postretirement benefits	(173)	(249)
Net liability	(176)	(256)
Accumulated other comprehensive income (loss), before tax:
Net actuarial gain (loss)	(298)	(394)
Prior service credit (cost)	(5)	(6)
Total	(303)	(400)
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	(46)	(48)
Net liability	(49)	(51)
Accumulated other comprehensive income (loss), before tax:
Net actuarial gain (loss)	(9)	(11)
Prior service credit (cost)	4	7
Total	$ (5)	$ (4)