Earnings Per Share (Tables)

3 Months Ended

Mar. 31, 2017

Earnings Per Share [Abstract]

Earnings per share

	Three Months Ended March 31,
	2017		2016
Net income (loss) attributable to AK Steel Holding Corporation	$	62.5	$	(13.6	)
Less: distributed earnings to common stockholders and holders of certain stock compensation awards	—		—
Undistributed earnings (loss)	$	62.5	$	(13.6	)
Common stockholders earnings—basic and diluted:
Distributed earnings to common stockholders	$	—	$	—
Undistributed earnings (loss) to common stockholders	62.4		(13.5		)
Common stockholders earnings (loss)—basic and diluted	$	62.4	$	(13.5	)
Common shares outstanding (weighted-average shares in millions):
Common shares outstanding for basic earnings per share	314.1		177.5
Effect of exchangeable debt	10.3		—
Effect of dilutive stock-based compensation	1.2		—
Common shares outstanding for diluted earnings per share	325.6		177.5
Basic earnings per share:
Distributed earnings	$	—	$	—
Undistributed earnings (loss)	0.20		(0.08		)
Basic earnings (loss) per share	$	0.20	$	(0.08	)
Diluted earnings per share:
Distributed earnings	$	—	$	—
Undistributed earnings (loss)	0.19		(0.08		)
Diluted earnings (loss) per share	$	0.19	$	(0.08	)
Potentially issuable common shares (in millions) excluded from earnings per share calculation due to anti-dilutive effect	1.1		3.9