Earnings Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 24.1us-gaap_ProfitLoss	$ 29.5us-gaap_ProfitLoss	$ 37.6us-gaap_ProfitLoss	$ 64.1us-gaap_ProfitLoss
Less: earnings and dividends allocated to participating securities	0	(0.1)	(0.1)	(0.2)
Earnings available for Carpenter common stockholders used in calculation of basic earnings per share	24.1us-gaap_UndistributedEarnings	29.4us-gaap_UndistributedEarnings	37.5us-gaap_UndistributedEarnings	63.9us-gaap_UndistributedEarnings
Weighted average number of common shares outstanding, basic (in shares)	53.4	53.2	53.5	53.2
Basic earnings per common share (in dollars per share)	$ 0.45us-gaap_EarningsPerShareBasic	$ 0.55us-gaap_EarningsPerShareBasic	$ 0.70us-gaap_EarningsPerShareBasic	$ 1.20us-gaap_EarningsPerShareBasic
Earnings available for Carpenter common stockholders used in calculation of diluted earnings per share	$ 24.1us-gaap_UndistributedEarningsDiluted	$ 29.4us-gaap_UndistributedEarningsDiluted	$ 37.5us-gaap_UndistributedEarningsDiluted	$ 63.9us-gaap_UndistributedEarningsDiluted
Effect of shares issuable under share-based compensation plans (in shares)	0.2	0.4	0.2	0.3
Weighted average number of common shares outstanding, diluted (in shares)	53.6	53.6	53.7	53.5
Diluted earnings per common share (in dollars per share)	$ 0.45us-gaap_EarningsPerShareDiluted	$ 0.55us-gaap_EarningsPerShareDiluted	$ 0.70us-gaap_EarningsPerShareDiluted	$ 1.19us-gaap_EarningsPerShareDiluted

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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The earnings that is allocated to common stock and participating securities to the extent that each security may share in earnings as if all of the earnings for the period had been distributed.

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The earnings that is allocated to common stock and participating securities to the extent that each security may share in earnings as if all of the earnings for the period had been distributed. Includes the adjustments resulting from the assumption that dilutive securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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Amount of undistributed earnings (loss) allocated to participating securities for the basic earnings (loss) per share or per unit calculation under the two-class method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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