Pension and Other Postretirement Benefits (Funded Status Recorded on Accompanying Balance Sheets) (Details) - USD ($) $ in Millions	Apr. 30, 2020	Apr. 30, 2019
Funded status is recorded on the accompanying consolidated balance sheets
Accrued postretirement benefits	$ (297)	$ (197)
Pension Benefits [Member]
Funded status is recorded on the accompanying consolidated balance sheets
Other assets	0	2
Accounts payable and accrued expenses	(7)	(6)
Accrued postretirement benefits	(249)	(150)
Net liability	(256)	(154)
Accumulated other comprehensive income (loss), before tax:
Net actuarial gain (loss)	(394)	(298)
Prior service credit (cost)	(6)	(8)
Total	(400)	(306)
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	(48)	(47)
Net liability	(51)	(50)
Accumulated other comprehensive income (loss), before tax:
Net actuarial gain (loss)	(11)	(10)
Prior service credit (cost)	7	10
Total	$ (4)	$ 0