Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2018		Apr. 30, 2017		Apr. 30, 2016
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 7		$ 9		$ 10
Additions Charged to Costs and Expenses	0		0		1
Additions Charged to Other Accounts	0		0		0
Deductions	0	[1]	2	[1]	2
Balance at End of Period	7		7		9
Valuation Allowance of Deferred Tax Assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	30		25		27
Additions Charged to Costs and Expenses	3		5		3
Additions Charged to Other Accounts	1		2		0
Deductions	5		2		5
Balance at End of Period	$ 29		$ 30		$ 25

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