Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2017		Apr. 30, 2016		Apr. 30, 2015
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 9		$ 10		$ 9
Additions Charged to Costs and Expenses	0		1		2
Additions Charged to Other Accounts	0		0		0
Deductions	2	[1]	2	[1]	1
Balance at End of Period	7		9		10
Valuation Allowance of Deferred Tax Assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	25		27		34
Additions Charged to Costs and Expenses	5		3		2
Additions Charged to Other Accounts	2		0		0
Deductions	2		5		9
Balance at End of Period	$ 30		$ 25		$ 27

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