Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Jul. 31, 2021	Jul. 31, 2020
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Sponsor Location [Extensible List]
Service cost	$ 7	$ 7
Interest cost	5	6
Expected return on plan assets	(11)	(12)
Amortization of:
Net actuarial loss	6	7
Net cost	$ 7	$ 8
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Sponsor Location [Extensible List]
Interest cost	$ 0	$ 1
Amortization of:
Prior service cost (credit)	0	(1)
Net cost	$ 0	$ 0