Earnings per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2011
Earnings per Common Share
Net income attributable to Carpenter	$ 40.9	$ 32.9	$ 33.0	$ 39.2	$ 40.8	$ 33.0	$ 23.6	$ 23.8	$ 146.1	$ 121.2	$ 71.0
Less: earnings and dividends allocated to participating securities									(0.8)	(1.1)	(0.8)
Earnings available to Carpenter common shareholders									$ 145.3	$ 120.1	$ 70.2
Weighted average number of common shares outstanding, basic	52.9	52.9	52.9	52.8	52.6	47.2	44.4	44.3	52.9	47.1	44.1
Basic earnings per common share (in dollars per share)	$ 0.77	$ 0.62	$ 0.62	$ 0.74	$ 0.77	$ 0.69	$ 0.53	$ 0.53	$ 2.75	$ 2.55	$ 1.59
Effect of shares issuable under share based compensation plans									0.5	0.7	0.6
Weighted average number of common shares outstanding, diluted	53.5	53.5	53.5	53.4	53.3	47.9	45.1	45.1	53.4	47.8	44.7
Diluted earnings per common share (in dollars per share)	$ 0.77	$ 0.62	$ 0.62	$ 0.74	$ 0.77	$ 0.69	$ 0.52	$ 0.53	$ 2.73	$ 2.53	$ 1.59