Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Jan. 31, 2014	Jan. 31, 2014	Jan. 31, 2013	Apr. 30, 2013
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits that would impact effective tax rate	$ 127.5	$ 127.5	$ 146.6	$ 146.4
Unrecognized Tax Benefits, Period Increase (Decrease)		(18.9)	59.8
Effect of anticipated settlements of audit issues and expiring statutes of limitations	35	35
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Other Information		23.2
Effective tax rate, excluding discrete tax items		39.20%	38.70%
Effective Income Tax Rate, Continuing Operations		39.70%	47.70%
Net Discrete Tax Expense (Benefit)	$ 3.7		$ 38.7