Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022	Jan. 31, 2021
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	$ 20	$ 20
Interest cost	5	6	16	19
Expected return on plan assets	(11)	(12)	(34)	(35)
Amortization of prior service cost (credit)	0	0	1	1
Amortization of net actuarial loss (gain)	6	7	18	20
Settlement loss	0	0	1	0
Net cost	7	8	$ 22	$ 25
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Sponsor Location [Extensible List]
Service cost	0	0	$ 1	$ 1
Interest cost	0	1	1	1
Amortization of prior service cost (credit)	0	(1)	(1)	(2)
Net cost	$ 0	$ 0	$ 1	$ 0