Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]
Net income (loss) attributable to AK Steel Holding Corporation	$ (86.1)	$ (9.9)
Less: distributed earnings to common stockholders and holders of certain stock compensation awards	0	0
Undistributed earnings (losses)	(86.1)	(9.9)
Common stockholders earnings - basic [Abstract]
Distributed earnings to common stockholders - basic	0	0
Undistributed earnings (loss) to common stockholders - basic	(85.8)	(9.8)
Common stockholders earnings (loss) - basic	(85.8)	(9.8)
Common stockholders earnings - diluted [Abstract]
Distributed earnings to common stockholders - diluted	0	0
Undistributed earnings (loss) to common stockholders - diluted	(85.8)	(9.8)
Common stockholders earnings (loss) - diluted	$ (85.8)	$ (9.8)
Common shares outstanding (weighted-average shares in millions) [Abstract]
Common shares outstanding for basic earnings per share (in shares)	136.1	135.7
Effect of exchangeable debt (in shares)	0	0
Effect of dilutive stock-based compensation (in shares)	0	0
Common shares outstanding for diluted earnings per share (in shares)	136.1	135.7
Basic earnings per share [Abstract]
Distributed earnings - basic (in dollars per share)	$ 0.00	$ 0.00
Undistributed earnings (loss) - basic (in dollars per share)	$ (0.63)	$ (0.07)
Basic earnings (loss) per share (in dollars per share)	$ (0.63)	$ (0.07)
Diluted earnings per share [Abstract]
Distributed earnings - diluted (in dollars per share)	$ 0.00	$ 0.00
Undistributed earnings (loss) - diluted (in dollars per share)	$ (0.63)	$ (0.07)
Diluted earnings (loss) per share (in dollars per share)	$ (0.63)	$ (0.07)
Potentially issuable common shares (in millions) excluded from earnings per share calculation due to anti-dilutive effect (in shares)	7.9	2.4