Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2019		Apr. 30, 2018		Apr. 30, 2017
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		$ 9
Additions Charged to Costs and Expenses	1		0		0
Additions Charged to Other Accounts	0		0		0
Deductions	1	[1]	0	[1]	2
Balance at End of Period	7		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	29		30		25
Additions Charged to Costs and Expenses	1		3		5
Additions Charged to Other Accounts	1		1		2
Deductions	6		5		2
Balance at End of Period	$ 25		$ 29		$ 30

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