Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
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	country:US
Service cost	$ 6	$ 6	$ 12	$ 12
Interest cost	8	9	15	17
Expected return on plan assets	(12)	(12)	(23)	(24)
Amortization of:
Prior service cost (credit)	0	0	1	1
Net actuarial loss	5	5	9	10
Net cost	$ 7	$ 8	$ 14	$ 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]	country:US	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