Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020	Oct. 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	$ 7	$ 6	$ 20	$ 18
Interest cost	6	8	19	24
Expected return on plan assets	(12)	(12)	(35)	(35)
Amortization of:
Prior service cost (credit)	0	0	1	1
Net actuarial loss	7	5	20	14
Net cost	$ 8	7	$ 25	22
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
Service cost	$ 0	0	$ 1	1
Interest cost	1	1	1	1
Amortization of:
Prior service cost (credit)	(1)	(1)	(2)	(2)
Net cost	$ 0	$ 0	$ 0	$ 0