Stock-Based Compensation (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Tax benefit of stock-based compensation	$ 7.6	$ 5.8	$ 5.4
Stock-based compensation expenses	20.1	15.3	14.2
Realized tax benefits	10.6	5.0	4.4
Shares reserved for future awards under stock-based compensation plans	10.5
Stock Options
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Intrinsic value of options exercised	13.6	6.0	1.0
Unrecognized compensation cost	1.0
Weighted-average period of recognition (years)	1 year
Nonvested Shares
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Fair value of shares vesting during period	8.6	7.2	11.9
Unrecognized compensation cost	23.5
Weighted-average period of recognition (years)	2 years
Nonvested Shares And Performance Nonvested [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Fair value of shares vesting during period		$ 0	$ 0
2003 Long-Term Executive Compensation Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Vesting period (in years), minimum	3 years
Minimum [Member] | 2003 Long-Term Executive Compensation Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Vesting period (in years), minimum	3 years
Maximum [Member] | 2003 Long-Term Executive Compensation Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Vesting period (in years), minimum	4 years