Earnings Per Share (Tables)

9 Months Ended

Sep. 30, 2015

Earnings Per Share [Abstract]

Earnings per share

	Three Months Ended September 30,					Nine Months Ended September 30,
	2015		2014			2015			2014
Net income (loss) attributable to AK Steel Holding Corporation	$	6.7	$	(7.2	)	$	(363.6	)	$	(110.4	)
Less: distributed earnings to common stockholders and holders of certain stock compensation awards	—		—			—			—
Undistributed earnings (loss)	$	6.7	$	(7.2	)	$	(363.6	)	$	(110.4	)
Common stockholders earnings—basic and diluted:
Distributed earnings to common stockholders	$	—	$	—		$	—		$	—
Undistributed earnings (loss) to common stockholders	6.6		(7.2		)	(362.4		)	(110.0		)
Common stockholders earnings (loss)—basic and diluted	$	6.6	$	(7.2	)	$	(362.4	)	$	(110.0	)
Common shares outstanding (weighted-average shares in millions):
Common shares outstanding for basic earnings per share	177.2		142.8			177.1			138.4
Effect of exchangeable debt	—		—			—			—
Effect of dilutive stock-based compensation	0.3		—			—			—
Common shares outstanding for diluted earnings per share	177.5		142.8			177.1			138.4
Basic and diluted earnings per share:
Distributed earnings	$	—	$	—		$	—		$	—
Undistributed earnings (loss)	0.04		(0.05		)	(2.05		)	(0.79		)
Basic and diluted earnings (loss) per share	$	0.04	$	(0.05	)	$	(2.05	)	$	(0.79	)
Potentially issuable common shares (in millions) excluded from earnings per share calculation due to anti-dilutive effect	3.4		13.3			3.0			10.6