Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019	Jul. 31, 2019
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Sponsor Location [Extensible List]	country:US		country:US		country:US
Service cost	$ 6	$ 6	$ 13	$ 12
Interest cost	6	8	12	15
Expected return on plan assets	(11)	(12)	(23)	(23)
Amortization of:
Prior service cost (credit)	0	0	1	1
Net actuarial loss	7	5	13	9
Net cost	$ 8	7	$ 16	14
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Sponsor Location [Extensible List]	country:US		country:US		country:US
Interest cost	$ 1	1	$ 1	1
Amortization of:
Prior service cost (credit)	(1)	(1)	(1)	(1)
Net cost	$ 0	$ 0	$ 0	$ 0