Earnings Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Common Share
Net income attributable to Carpenter	$ 33.0	$ 23.6	$ 72.2	$ 47.4
Less: earnings and dividends allocated to participating securities	(0.2)	(0.2)	(0.4)	(0.4)
Earnings available for Carpenter common shareholders	$ 32.8	$ 23.4	$ 71.8	$ 47.0
Weighted average number of common shares outstanding, basic	52.9	44.4	52.8	44.4
Effect of shares issuable under share based compensation plans	0.6	0.7	0.6	0.7
Weighted average number of common shares outstanding, diluted	53.5	45.1	53.4	45.1
Basic earnings per common share (in dollars per share)	$ 0.62	$ 0.53	$ 1.36	$ 1.06
Diluted earnings per common share (in dollars per share)	$ 0.62	$ 0.52	$ 1.35	$ 1.05