Pension and Other Postretirement Benefits (Schedule of Components of Pension Expense) (Details) - Pension Benefits [Member] - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Pension Expense
Service cost	$ 26	$ 24	$ 24
Interest cost	25	31	34
Expected return on assets	(46)	(46)	(47)
Amortization of prior service cost (credit)	1	1	1
Amortization of net actuarial loss (gain)	27	19	19
Settlement charge	0	1	15
Net cost	$ 33	$ 30	$ 46