Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Net income (loss) attributable to AK Steel Holding Corporation	$ (13.6)	$ (306.3)
Less: distributed earnings to common stockholders and holders of certain stock compensation awards	0.0	0.0
Undistributed Earnings Attributable To Parent	(13.6)	(306.3)
Common stockholders earnings - basic [Abstract]
Distributed earnings to common stockholders - basic	0.0	0.0
Undistributed earnings (loss) to common stockholders - basic	(13.5)	(305.1)
Common stockholders earnings (loss) - basic	(13.5)	(305.1)
Common stockholders earnings - diluted [Abstract]
Distributed earnings to common stockholders - diluted	0.0	0.0
Undistributed earnings (loss) to common stockholders - diluted	(13.5)	(305.1)
Common stockholders earnings (loss) - diluted	$ (13.5)	$ (305.1)
Common shares outstanding (weighted-average shares in millions) [Abstract]
Common shares outstanding for basic earnings per share (in shares)	177.5	177.0
Effect of exchangeable debt (in shares)	0.0	0.0
Effect of dilutive stock-based compensation (in shares)	0.0	0.0
Common shares outstanding for diluted earnings per share (in shares)	177.5	177.0
Basic earnings per share [Abstract]
Distributed earnings - basic (in dollars per share)	$ 0.00	$ 0.00
Undistributed earnings (loss) - basic (in dollars per share)	(0.08)	(1.72)
Basic earnings (loss) per share (in dollars per share)	(0.08)	(1.72)
Diluted earnings per share [Abstract]
Distributed earnings - diluted (in dollars per share)	0.00	0.00
Undistributed earnings (loss) - diluted (in dollars per share)	(0.08)	(1.72)
Diluted earnings (loss) per share (in dollars per share)	$ (0.08)	$ (1.72)
Potentially issuable common shares (in millions) excluded from earnings per share calculation due to anti-dilutive effect (in shares)	3.9	3.0