Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Oct. 31, 2013	Oct. 31, 2013	Oct. 31, 2012	Apr. 30, 2013
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits that would impact effective tax rate	$ 129.8	$ 129.8	$ 207.4	$ 146.4
Unrecognized Tax Benefits, Period Increase (Decrease)		(16.6)	1.0
Effect of anticipated settlements of audit issues and expiring statutes of limitations	23	23
Effective tax rate, excluding discrete tax items		38.70%	38.90%
Effective Income Tax Rate, Continuing Operations		40.60%	37.60%
Net Discrete Tax Expense (Benefit)	$ 6.9		$ 4.2