Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019		Apr. 30, 2018
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 7	$ 7		$ 7
Additions Charged to Costs and Expenses	4	1		0
Additions Charged to Other Accounts	0	0		0
Deductions	0	1	[1]	0
Balance at End of Period	11	7		7
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	25	29		30
Additions Charged to Costs and Expenses	2	1		3
Additions Charged to Other Accounts	0	1		1
Deductions	5	6		5
Balance at End of Period	$ 22	$ 25		$ 29

[1] Doubtful accounts written off, net of recoveries.