Pension and Other Postretirement Benefits (Schedule of Components of Pension Expense) (Details) - Pension Benefits [Member] - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Pension Expense
Service cost	$ 24	$ 24	$ 26
Interest cost	34	29	35
Expected return on assets	(47)	(41)	(41)
Amortization of prior service cost (credit)	1	1	1
Amortization of net actuarial loss (gain)	19	21	25
Settlement charge	15	0	1
Net cost	$ 46	$ 34	$ 47