CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net sales	$ 1,445.7	$ 1,535.5	$ 1,680.5	$ 1,697.7	$ 1,677.1	$ 1,735.6	$ 1,746.6	$ 1,658.9	$ 6,359.4	$ 6,818.2	$ 6,080.5
Cost of products sold (exclusive of items shown separately below)									5,606.3	5,911.0	5,253.1
Selling and administrative expenses									295.2	322.6	284.9
Depreciation									192.6	220.2	226.0
Ashland Works closure									56.0	0.0	0.0
Credit for adjustment of liability for transportation costs									0.0	0.0	(19.3)
Asset impairment charge									0.0	0.0	75.6
Total operating costs									6,150.1	6,453.8	5,820.3
Operating profit	10.4	51.1	106.6	41.2	86.5	114.8	99.5	63.6	209.3	364.4	260.2
Interest expense									146.6	151.6	152.3
Pension and OPEB (income) expense									12.0	(19.2)	(71.9)
Other (income) expense									(18.5)	(5.9)	17.1
Income before income taxes									69.2	237.9	162.7
Income tax expense (benefit)									6.2	(6.2)	(2.2)
Net income									63.0	244.1	164.9
Less: Net income attributable to noncontrolling interests									51.8	58.1	61.4
Net income attributable to AK Steel Holding Corporation	$ (53.9)	$ 2.8	$ 66.8	$ (4.5)	$ 33.5	$ 67.2	$ 56.6	$ 28.7	$ 11.2	$ 186.0	$ 103.5
Basic and diluted earnings per share:
Earnings Per Share, Basic									$ 0.04	$ 0.59	$ 0.33
Earnings Per Share, Diluted									$ 0.04	$ 0.59	$ 0.32