Income Taxes (Unrecognized Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 11	$ 13	$ 40
Additions for tax positions provided in prior periods	1	2	0
Additions for tax positions provided in current period	1	1	7
Decreases for tax positions provided in prior years	1	1	5
Settlements of tax positions in the current period	(1)	(3)	(27)
Lapse of statutes of limitations	0	(1)	(2)
Unrecognized tax benefits at end of year	$ 11	$ 11	$ 13