Schedule II - Valuation and Qualifying Accounts (Details) (Allowance for Doubtful Accounts [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Apr. 30, 2015		Apr. 30, 2014		Apr. 30, 2013
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 9		$ 9		$ 9
Additions Charged to Costs and Expenses	2		0		2
Additions Charged to Other Accounts	0		0		0
Deductions	1	[1]	0	[1]	2
Balance at End of Period	$ 10		$ 9		$ 9

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