Earnings Per Share (Tables)

6 Months Ended

Jun. 30, 2018

Earnings Per Share [Abstract]

Earnings per share

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Net income (loss) attributable to AK Steel Holding Corporation	$	56.6	$	77.2	$	85.3	$	161.6
Less: distributed earnings to common stockholders and holders of certain stock compensation awards	—		—		—		—
Undistributed earnings	$	56.6	$	77.2	$	85.3	$	161.6
Common stockholders earnings—basic and diluted:
Distributed earnings to common stockholders	$	—	$	—	$	—	$	—
Undistributed earnings to common stockholders	56.6		77.1		85.2		161.4
Common stockholders earnings—basic and diluted	$	56.6	$	77.1	$	85.2	$	161.4
Common shares outstanding (weighted-average shares in millions):
Common shares outstanding for basic earnings per share	314.7		314.3		314.7		314.2
Effect of exchangeable debt	—		3.9		—		7.6
Effect of dilutive stock-based compensation	1.0		0.8		1.0		1.0
Common shares outstanding for diluted earnings per share	315.7		319.0		315.7		322.8
Basic earnings per share:
Distributed earnings	$	—	$	—	$	—	$	—
Undistributed earnings	0.18		0.25		0.27		0.51
Basic earnings per share	$	0.18	$	0.25	$	0.27	$	0.51
Diluted earnings per share:
Distributed earnings	$	—	$	—	$	—	$	—
Undistributed earnings	0.18		0.24		0.27		0.50
Diluted earnings per share	$	0.18	$	0.24	$	0.27	$	0.50
Potentially issuable common shares (in millions) excluded from earnings per share calculation due to anti-dilutive effect	2.5		1.5		2.3		1.1