Comprehensive Income (Loss) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Comprehensive Income (Loss), Net of Tax [Abstract]
Net income (loss) attributable to AK Steel Holding Corporation	$ (3.5)	$ (59.2)	$ 38.3	$ (30.6)
Other comprehensive income (loss), net of tax:
Foreign currency translation gain (loss)	(1.5)	1.7	0	(0.4)
Cash flow hedges:
Gains (losses) arising in period	(2.9)	(4.7)	(3.1)	(19.6)
Less: Reclassification of losses (gains) included in net income	(1.2)	6.4	2.1	9.3
Unrealized holding gains (losses) on investments:
Unrealized holding gains (losses) arising during period	(0.7)	1.1	(0.6)	0.4
Less: Reclassification of losses (gains) included in net income	0	0	0	0.1
Pension and OPEB adjustment	(8.6)	(10.4)	(46.5)	(29.9)
Comprehensive income (loss)	(18.4)	(65.1)	(9.8)	(70.7)
Accumulated Other Comprehensive Income, Net of Tax [Abstract]
Foreign currency translation	3.5		3.5		3.5
Cash flow hedges	(1.4)		(1.4)		(0.4)
Unrealized gain (loss) on investments	(0.9)		(0.9)		(0.3)
Employee benefit liability	43.3		43.3		89.8
Accumulated other comprehensive income	$ 44.5		$ 44.5		$ 92.6