Earnings per Share (Tables)

3 Months Ended

Jul. 31, 2013

Earnings Per Share [Abstract]

Computation of earnings per common share, basic and diluted

	Three Months Ended July 31,
	2013		2012
Net income	$	126.6	$	110.9
Net income allocated to participating securities		1.1		1.0
Net income allocated to common stockholders	$	125.5	$	109.9
Weighted-average common shares outstanding		105,077,523		109,418,592
Dilutive effect of stock options		16,755		29,536
Weighted-average common shares outstanding—assuming dilution		105,094,278		109,448,128
Net income per common share	$	1.19	$	1.00
Net income per common share—assuming dilution	$	1.19	$	1.00