Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Net income (loss) attributable to AK Steel Holding Corporation	$ (31.7)	$ (60.9)	$ (82.0)	$ (796.9)
Less: distributed earnings to common stockholders and holders of certain stock compensation awards	0	0	0	11.0
Undistributed earnings (losses)	(31.7)	(60.9)	(82.0)	(807.9)
Common stockholders earnings - basic [Abstract]
Distributed earnings to common stockholders - basic	0	0	0	11.0
Undistributed earnings (loss) to common stockholders - basic	(31.6)	(60.6)	(81.7)	(804.9)
Common stockholders earnings (loss) - basic	(31.6)	(60.6)	(81.7)	(793.9)
Common stockholders earnings - diluted [Abstract]
Distributed earnings to common stockholders - diluted	0	0	0	11.0
Undistributed earnings (loss) to common stockholders - diluted	(31.6)	(60.6)	(81.7)	(804.9)
Common stockholders earnings (loss) - diluted	$ (31.6)	$ (60.6)	$ (81.7)	$ (793.9)
Common shares outstanding (weighted-average shares in millions) [Abstract]
Common shares outstanding for basic earnings per share (in shares)	135.9	110.2	135.8	110.1
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)	135.9	110.2	135.8	110.1
Basic earnings per share [Abstract]
Distributed earnings - basic (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.10
Undistributed earnings (loss) - basic (in dollars per share)	$ (0.23)	$ (0.55)	$ (0.60)	$ (7.31)
Basic earnings (loss) per share (in dollars per share)	$ (0.23)	$ (0.55)	$ (0.60)	$ (7.21)
Diluted earnings per share [Abstract]
Distributed earnings - diluted (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.10
Undistributed earnings (loss) - diluted (in dollars per share)	$ (0.23)	$ (0.55)	$ (0.60)	$ (7.31)
Diluted earnings (loss) per share (in dollars per share)	$ (0.23)	$ (0.55)	$ (0.60)	$ (7.21)
Antidilutive securities excluded from earnings per share [Abstract]
Potentially issuable common shares (in millions) excluded from earnings per share calculation due to anti-dilutive effect (in shares)	2.5	2.0	2.5	2.0