Pension and Other Postretirement Benefits (Change in Benefit Obligation) (Details) - USD ($) $ in Millions		12 Months Ended
		Apr. 30, 2023	Apr. 30, 2022	Apr. 30, 2021
Pension Benefits [Member]
Changes in present value of pension and other postretirement benefits
Obligation at beginning of year		$ 846	$ 1,012
Service cost		20	26	$ 26
Interest cost		32	22	25
Net actuarial loss (gain)1	[1]	(21)	(132)
Retiree contributions		0	0
Benefits paid		(146)	(82)
Obligation at end of year		731	846	1,012
Medical and Life Insurance Benefits [Member]
Changes in present value of pension and other postretirement benefits
Obligation at beginning of year		43	49
Service cost		1	1	1
Interest cost		1	1	1
Net actuarial loss (gain)1	[1]	(2)	(5)
Retiree contributions		2	1
Benefits paid		(5)	(4)
Obligation at end of year		$ 40	$ 43	$ 49

[1] The net actuarial loss (gain) during each year was primarily attributable to changes in discount rates