Earnings Per Share (Tables)

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Earnings per share

	Three Months Ended March 31,
	2018		2017
Net income (loss) attributable to AK Steel Holding Corporation	$	28.7	$	84.4
Less: distributed earnings to common stockholders and holders of certain stock compensation awards	—		—
Undistributed earnings	$	28.7	$	84.4
Common stockholders earnings—basic and diluted:
Distributed earnings to common stockholders	$	—	$	—
Undistributed earnings to common stockholders	28.6		84.3
Common stockholders earnings—basic and diluted	$	28.6	$	84.3
Common shares outstanding (weighted-average shares in millions):
Common shares outstanding for basic earnings per share	314.7		314.1
Effect of exchangeable debt	0.5		10.3
Effect of dilutive stock-based compensation	0.8		1.2
Common shares outstanding for diluted earnings per share	316.0		325.6
Basic earnings per share:
Distributed earnings	$	—	$	—
Undistributed earnings	0.09		0.27
Basic earnings per share	$	0.09	$	0.27
Diluted earnings per share:
Distributed earnings	$	—	$	—
Undistributed earnings	0.09		0.26
Diluted earnings per share	$	0.09	$	0.26
Potentially issuable common shares (in millions) excluded from earnings per share calculation due to anti-dilutive effect	2.2		1.1