Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]
Net income attributable to Carpenter									$ 58.7	$ 132.8	$ 146.1
Less: earnings and dividends allocated to participating securities									(0.1)	(0.4)	(0.8)
Earnings available for Carpenter common shareholders used in calculation of basic earnings per share									$ 58.6	$ 132.4	$ 145.3
Weighted average number of common shares outstanding, basic (in shares)	50.9	52.6	53.4	53.5	53.4	53.3	53.2	53.1	52.6	53.3	52.9
Basic earnings per common share (in dollars per share)	$ 0.44	$ (0.03)	$ 0.45	$ 0.25	$ 0.71	$ 0.57	$ 0.55	$ 0.65	$ 1.11	$ 2.48	$ 2.75
Earnings available for Carpenter common shareholders used in calculation of diluted earnings per share									$ 58.6	$ 132.4	$ 145.3
Effect of shares issuable under share-based compensation plans (in shares)									0.1	0.3	0.3
Weighted average number of common shares outstanding, diluted (in shares)	51.0	52.6	53.6	53.7	53.8	53.7	53.6	53.4	52.7	53.6	53.2
Diluted earnings per common share (in dollars per share)	$ 0.44	$ (0.03)	$ 0.45	$ 0.25	$ 0.71	$ 0.57	$ 0.55	$ 0.65	$ 1.11	$ 2.47	$ 2.73