Pension and Other Postretirement Benefits (Change in Benefit Obligation) (Details) - USD ($) $ in Millions		12 Months Ended
		Apr. 30, 2022	Apr. 30, 2021	Apr. 30, 2020
Pension Benefits [Member]
Changes in present value of pension and other postretirement benefits
Obligation at beginning of year		$ 1,012	$ 1,005
Service cost		26	26	$ 24
Interest cost		22	25	31
Net actuarial loss (gain)1	[1]	(132)	9
Retiree contributions		0	0
Benefits paid		(82)	(53)
Obligation at end of year		846	1,012	1,005
Medical and Life Insurance Benefits [Member]
Changes in present value of pension and other postretirement benefits
Obligation at beginning of year		49	51
Service cost		1	1	1
Interest cost		1	1	1
Net actuarial loss (gain)1	[1]	(5)	(1)
Retiree contributions		1	1
Benefits paid		(4)	(4)
Obligation at end of year		$ 43	$ 49	$ 51

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