Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2021		Apr. 30, 2020	Apr. 30, 2019
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	$ 11		$ 7	$ 7
Additions Charged to Costs and Expenses	0		4	1
Additions Charged to Other Accounts	0		0	0
Deductions	4	[1]	0	1	[1]
Balance at End of Period	7		11	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	22		25	29
Additions Charged to Costs and Expenses	10		2	1
Additions Charged to Other Accounts	0		0	1
Deductions	12		5	6
Balance at End of Period	$ 20		$ 22	$ 25

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