Earnings per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2010
Earnings per Common Share
Net income attributable to Carpenter	$ 40.8	$ 33.0	$ 23.6	$ 23.8	$ 25.5	$ 28.6	$ 9.3	$ 7.6	$ 121.2	$ 71.0	$ 2.1
Less: earnings and dividends allocated to participating securities									(1.1)	(0.8)	(0.2)
Earnings available for Carpenter common shareholders									$ 120.1	$ 70.2	$ 1.9
Weighted average common shares outstanding, basic	52.6	47.2	44.4	44.3	44.2	44.1	44.1	44.1	47.1	44.1	43.9
Effect of shares issuable under share based compensation plans									0.7	0.6	0.5
Weighted average number of common shares outstanding, diluted	53.3	47.9	45.1	45.1	45.0	44.7	44.7	44.5	47.8	44.7	44.4
Basic earnings per common share (in dollars per share)	$ 0.77	$ 0.69	$ 0.53	$ 0.53	$ 0.57	$ 0.64	$ 0.21	$ 0.17	$ 2.55	$ 1.59	$ 0.04
Diluted earnings per common share (in dollars per share)	$ 0.77	$ 0.69	$ 0.52	$ 0.53	$ 0.57	$ 0.64	$ 0.21	$ 0.17	$ 2.53	$ 1.59	$ 0.04