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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The total amount of dividends declared in the period for each class of stock and the contractual amount of dividends (or interest on participating income bonds) that must be paid for the period (for example, unpaid cumulative dividends). Dividends declared in the current period do not include dividends declared in respect of prior-period unpaid cumulative dividends. Preferred dividends that are cumulative only if earned are deducted only to the extent that they are earned.

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Amount of paid and unpaid cash, stock, and paid-in-kind (PIK) dividends declared, for example, but not limited to, common and preferred stock.

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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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Dividends declared in the period and the contractual amount of dividends (or interest on participating income bonds) that must be paid per security.

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The earnings attributable to each security on the basis that all of the earnings for the period had been distributed (to the extent that each security may share in earnings). This is the earnings amount which reflects the participation rights in undistributed earnings of each security.

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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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Dividends declared in the period and the contractual amount of dividends (or interest on participating income bonds) that must be paid per security, taking into account all dilutive potential common shares outstanding during the period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method.

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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 portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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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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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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Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income (loss) attributable to AK Steel Holding Corporation	$ 13.5us-gaap_NetIncomeLoss	$ (7.2)us-gaap_NetIncomeLoss	$ (17.1)us-gaap_NetIncomeLoss	$ (86.1)us-gaap_NetIncomeLoss	$ 35.2us-gaap_NetIncomeLoss	$ (31.7)us-gaap_NetIncomeLoss	$ (40.4)us-gaap_NetIncomeLoss	$ (9.9)us-gaap_NetIncomeLoss	$ (96.9)us-gaap_NetIncomeLoss	$ (46.8)us-gaap_NetIncomeLoss	$ (1,027.3)us-gaap_NetIncomeLoss
Less: distributed earnings to common stockholders and holders of certain stock compensation awards									0us-gaap_Dividends	0us-gaap_Dividends	11.0us-gaap_Dividends
Undistributed earnings (loss)									(96.9)	(46.8)	(1,038.3)
Common stockholders earnings - basic [Abstract]
Distributed earnings to common stockholders									0us-gaap_DistributedEarnings	0us-gaap_DistributedEarnings	11.0us-gaap_DistributedEarnings
Undistributed earnings (loss) to common stockholders - basic									(96.6)us-gaap_UndistributedEarnings	(46.6)us-gaap_UndistributedEarnings	(1,034.6)us-gaap_UndistributedEarnings
Common stockholders earnings (loss) - basic									(96.6)	(46.6)	(1,023.6)
Common stockholders earnings - diluted [Abstract]
Distributed earnings to common stockholders									0us-gaap_DistributedEarnings	0us-gaap_DistributedEarnings	11.0us-gaap_DistributedEarnings
Undistributed earnings to common stockholders - diluted									(96.6)us-gaap_UndistributedEarningsDiluted	(46.6)us-gaap_UndistributedEarningsDiluted	(1,034.6)us-gaap_UndistributedEarningsDiluted
Common stockholders earnings - diluted									$ (96.6)	$ (46.6)	$ (1,023.6)
Common shares outstanding (weighted-average shares in millions) [Abstract]
Common shares outstanding for basic earnings per share (in shares)									148.1	135.8	113.0
Effect of exchangeable debt									0	0	0
Effect of dilutive stock-based compensation (in shares)									0	0	0
Common shares outstanding for diluted earnings per share (in shares)									148.1	135.8	113.0
Basic earnings per share [Abstract]
Distributed earnings - basic (in dollars per share)									$ 0.00	$ 0.00	$ 0.10
Undistributed earnings (loss) - basic (in dollars per share)									$ (0.65)	$ (0.34)	$ (9.16)
Basic earnings (loss) per share (in dollars per share)	$ 0.08us-gaap_EarningsPerShareBasic	$ (0.05)us-gaap_EarningsPerShareBasic	$ (0.13)us-gaap_EarningsPerShareBasic	$ (0.63)us-gaap_EarningsPerShareBasic					$ (0.65)us-gaap_EarningsPerShareBasic	$ (0.34)us-gaap_EarningsPerShareBasic	$ (9.06)us-gaap_EarningsPerShareBasic
Diluted earnings per share [Abstract]
Distributed earnings - diluted (in dollars per share)									$ 0.00	$ 0.00	$ 0.10
Undistributed earnings (loss) - diluted (in dollars per share)									$ (0.65)	$ (0.34)	$ (9.16)
Diluted earnings (loss) per share (in dollars per share)	$ 0.07us-gaap_EarningsPerShareDiluted	$ (0.05)us-gaap_EarningsPerShareDiluted	$ (0.13)us-gaap_EarningsPerShareDiluted	$ (0.63)us-gaap_EarningsPerShareDiluted					$ (0.65)us-gaap_EarningsPerShareDiluted	$ (0.34)us-gaap_EarningsPerShareDiluted	$ (9.06)us-gaap_EarningsPerShareDiluted
Potentially issuable common shares excluded from earnings per share calculation due to anti-dilutive effect (in millions of shares)									9.7	2.6	2.4