Earnings per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2012
Earnings per Common Share
Net income attributable to Carpenter	$ 38.1	$ 30.6	$ 29.5	$ 34.6	$ 40.9	$ 32.9	$ 33.0	$ 39.2	$ 132.8	$ 146.1	$ 121.2
Less: earnings and dividends allocated to participating securities									(0.4)	(0.8)	(1.1)
Earnings available to Carpenter common stockholders used in calculation of basic earnings per share (in dollars per share)									132.4	145.3	120.1
Weighted average number of common shares outstanding, basic	53.4	53.3	53.2	53.1	52.9	52.9	52.9	52.8	53.3	52.9	47.1
Basic earnings per common share (in dollars per share)	$ 0.71	$ 0.57	$ 0.55	$ 0.65	$ 0.77	$ 0.62	$ 0.62	$ 0.74	$ 2.48	$ 2.75	$ 2.55
Earnings available to Carpenter common stockholders used in calculation of diluted earnings per share (in dollars per share)									$ 132.4	$ 145.3	$ 120.1
Effect of shares issuable under share-based compensation plans									0.3	0.3	0.4
Weighted average number of common shares outstanding, diluted	53.8	53.7	53.6	53.4	53.3	53.2	53.3	53.2	53.6	53.2	47.5
Diluted earnings per common share (in dollars per share)	$ 0.71	$ 0.57	$ 0.55	$ 0.65	$ 0.77	$ 0.62	$ 0.62	$ 0.74	$ 2.47	$ 2.73	$ 2.53