Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Oct. 31, 2021	Oct. 31, 2020	Oct. 31, 2021	Oct. 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	$ 6	$ 6	$ 13	$ 13
Interest cost	6	6	11	12
Expected return on plan assets	(11)	(11)	(23)	(23)
Amortization of prior service cost (credit)	0	0	1	1
Amortization of net actuarial loss (gain)	6	7	12	13
Settlement loss	1	0	1	0
Net cost	8	8	$ 15	$ 16
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	$ 1	$ 1
Amortization of prior service cost (credit)	0	(1)	(1)	(1)
Net cost	$ 0	$ 0	$ 0	$ 0