Shareholders' Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended
	Aug. 31, 2011	Nov. 30, 2010	Aug. 31, 2010	Nov. 30, 2011
Shareholders' Equity [Line Items]
Stock repurchase program, authorized amount	$ 100.0
Common stock repurchased (in shares)			344,847	2,290,059
Treasury stock acquired, average cost per share			$ 37.64	$ 43.49
Common stock, cost			13.0	99.6
Stock repurchase program, remaining authorized repurchase amount			13.0
Treasury stock retired, shares		344,847		2,290,059
Treasury stock retired, amount		$ 13.0		$ 99.6