Supplemental Guarantor Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	$ 1,383.5	$ 1,369.8
Cost of products sold (exclusive of items shown separately below)	1,335.6	1,252.3
Selling and administrative expenses (exclusive of items shown separately below)	60.2	51.6
Depreciation	48.7	48.6
Pension and OPEB expense (income)	(25.7)	(15.9)
Total operating costs	1,418.8	1,336.6
Operating profit (loss)	(35.3)	33.2
Interest expense	32.2	31.0
Other income (expense)	(1.9)	1.8
Income (loss) before income taxes	(69.4)	4.0
Income tax expense (benefit)	1.8	(2.8)
Equity in net income (loss) of subsidiaries	0	0
Net income (loss)	(71.2)	6.8
Less: Net income attributable to noncontrolling interests	14.9	16.7
Net income (loss) attributable to AK Steel Holding Corporation	(86.1)	(9.9)
Other comprehensive income (loss)	(24.2)	(19.7)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(110.3)	(29.6)
Current assets:
Cash and cash equivalents	31.1	191.8
Accounts receivable, net	498.9		525.2
Inventory, net	687.7		586.6
Deferred tax assets, current	70.4		69.6
Other current assets	38.2		46.5
Total current assets	1,326.3		1,273.2
Property, plant and equipment	5,884.4		5,871.9
Accumulated depreciation	(4,040.0)		(3,991.8)
Property, plant and equipment, net	1,844.4		1,880.1
Other non-current assets:
Investment in Magnetation LLC	186.5		187.8
Investment in affiliates	0		0
Inter-company accounts	0		0
Other non-current assets	258.2		264.6
TOTAL ASSETS	3,615.4		3,605.7
Current liabilities:
Accounts payable	617.4		601.8
Accrued liabilities	175.7		142.9
Current portion of long-term debt	0.6		0.8
Current portion of pension and other postretirement benefit obligations	73.4		85.9
Total current liabilities	867.1		831.4
Non-current liabilities:
Long-term debt	1,657.2		1,506.2
Pension and other postretirement benefit obligations	908.0		965.4
Other non-current liabilities	110.5		110.0
TOTAL LIABILITIES	3,542.8		3,413.0
Total stockholders' equity (deficit)	(328.2)		(221.0)
Noncontrolling interests	400.8		413.7
TOTAL EQUITY (DEFICIT)	72.6	(109.7)	192.7	(91.0)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,615.4		3,605.7
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities	(125.0)	(7.0)
Cash flows from investing activities:
Capital investments	(13.8)	(16.5)
Other investing items, net	6.8	0.8
Net cash flows from investing activities	(7.0)	(15.7)
Cash flows from financing activities:
Net borrowings under credit facility	150.0	0
Redemption of long-term debt	(0.2)	(0.2)
Debt issuance costs	(3.3)	(1.5)
Purchase of treasury stock	(0.9)	(0.6)
Inter-company activity	0	0
SunCoke Middletown distributions to noncontrolling interest owners	(27.8)	(9.1)
Other financing items, net	0	(1.1)
Net cash flows from financing activities	117.8	(12.5)
Net increase (decrease) in cash and cash equivalents	(14.2)	(35.2)
Cash and cash equivalents, beginning of period	45.3	227.0
Cash and cash equivalents, end of period	31.1	191.8
AK Holding [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	0	0
Cost of products sold (exclusive of items shown separately below)	0	0
Selling and administrative expenses (exclusive of items shown separately below)	1.6	1.5
Depreciation	0	0
Pension and OPEB expense (income)	0	0
Total operating costs	1.6	1.5
Operating profit (loss)	(1.6)	(1.5)
Interest expense	0	0
Other income (expense)	0	0
Income (loss) before income taxes	(1.6)	(1.5)
Income tax expense (benefit)	0	0
Equity in net income (loss) of subsidiaries	(84.5)	(8.4)
Net income (loss)	(86.1)	(9.9)
Less: Net income attributable to noncontrolling interests	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(86.1)	(9.9)
Other comprehensive income (loss)	(24.2)	(19.7)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(110.3)	(29.6)
Current assets:
Cash and cash equivalents	0	0
Accounts receivable, net	0		0
Inventory, net	0		0
Deferred tax assets, current	0		0
Other current assets	0.3		0.3
Total current assets	0.3		0.3
Property, plant and equipment	0		0
Accumulated depreciation	0		0
Property, plant and equipment, net	0		0
Other non-current assets:
Investment in Magnetation LLC	0		0
Investment in affiliates	(2,913.8)		(2,772.4)
Inter-company accounts	2,585.3		2,551.1
Other non-current assets	0		0
TOTAL ASSETS	(328.2)		(221.0)
Current liabilities:
Accounts payable	0		0
Accrued liabilities	0		0
Current portion of long-term debt	0		0
Current portion of pension and other postretirement benefit obligations	0		0
Total current liabilities	0		0
Non-current liabilities:
Long-term debt	0		0
Pension and other postretirement benefit obligations	0		0
Other non-current liabilities	0		0
TOTAL LIABILITIES	0		0
Total stockholders' equity (deficit)	(328.2)		(221.0)
Noncontrolling interests	0		0
TOTAL EQUITY (DEFICIT)	(328.2)		(221.0)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	(328.2)		(221.0)
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities	(1.3)	(1.3)
Cash flows from investing activities:
Capital investments	0	0
Other investing items, net	0	0
Net cash flows from investing activities	0	0
Cash flows from financing activities:
Net borrowings under credit facility	0
Redemption of long-term debt	0	0
Debt issuance costs	0	0
Purchase of treasury stock	(0.9)	(0.6)
Inter-company activity	2.2	1.9
SunCoke Middletown distributions to noncontrolling interest owners	0	0
Other financing items, net	0	0
Net cash flows from financing activities	1.3	1.3
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
AK Steel [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	1,315.1	1,283.7
Cost of products sold (exclusive of items shown separately below)	1,303.9	1,200.2
Selling and administrative expenses (exclusive of items shown separately below)	58.9	50.6
Depreciation	42.5	43.7
Pension and OPEB expense (income)	(25.7)	(15.9)
Total operating costs	1,379.6	1,278.6
Operating profit (loss)	(64.5)	5.1
Interest expense	31.7	30.7
Other income (expense)	(3.8)	(2.1)
Income (loss) before income taxes	(100.0)	(27.7)
Income tax expense (benefit)	(4.6)	(9.7)
Equity in net income (loss) of subsidiaries	10.9	9.6
Net income (loss)	(84.5)	(8.4)
Less: Net income attributable to noncontrolling interests	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(84.5)	(8.4)
Other comprehensive income (loss)	(24.2)	(19.7)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(108.7)	(28.1)
Current assets:
Cash and cash equivalents	15.6	152.4
Accounts receivable, net	452.8		492.4
Inventory, net	625.7		520.0
Deferred tax assets, current	70.2		69.4
Other current assets	34.1		43.9
Total current assets	1,198.4		1,142.5
Property, plant and equipment	5,262.3		5,258.4
Accumulated depreciation	(3,924.2)		(3,881.7)
Property, plant and equipment, net	1,338.1		1,376.7
Other non-current assets:
Investment in Magnetation LLC	0		0
Investment in affiliates	1,421.5		1,393.8
Inter-company accounts	(3,529.6)		(3,479.7)
Other non-current assets	133.4		141.0
TOTAL ASSETS	561.8		574.3
Current liabilities:
Accounts payable	565.4		550.5
Accrued liabilities	166.1		133.6
Current portion of long-term debt	0.6		0.8
Current portion of pension and other postretirement benefit obligations	72.9		85.4
Total current liabilities	805.0		770.3
Non-current liabilities:
Long-term debt	1,657.2		1,506.2
Pension and other postretirement benefit obligations	903.3		960.6
Other non-current liabilities	110.1		109.6
TOTAL LIABILITIES	3,475.6		3,346.7
Total stockholders' equity (deficit)	(2,913.8)		(2,772.4)
Noncontrolling interests	0		0
TOTAL EQUITY (DEFICIT)	(2,913.8)		(2,772.4)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	561.8		574.3
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities	(142.4)	(29.7)
Cash flows from investing activities:
Capital investments	(7.5)	(13.6)
Other investing items, net	7.0	1.6
Net cash flows from investing activities	(0.5)	(12.0)
Cash flows from financing activities:
Net borrowings under credit facility	150.0
Redemption of long-term debt	(0.2)	(0.2)
Debt issuance costs	(3.3)	(1.5)
Purchase of treasury stock	0	0
Inter-company activity	(4.8)	(6.0)
SunCoke Middletown distributions to noncontrolling interest owners	0	0
Other financing items, net	0	(1.8)
Net cash flows from financing activities	141.7	(9.5)
Net increase (decrease) in cash and cash equivalents	(1.2)	(51.2)
Cash and cash equivalents, beginning of period	16.8	203.6
Cash and cash equivalents, end of period	15.6	152.4
Other Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	192.6	216.8
Cost of products sold (exclusive of items shown separately below)	148.9	173.8
Selling and administrative expenses (exclusive of items shown separately below)	10.3	9.7
Depreciation	6.2	4.9
Pension and OPEB expense (income)	0	0
Total operating costs	165.4	188.4
Operating profit (loss)	27.2	28.4
Interest expense	0.5	0.3
Other income (expense)	1.9	3.9
Income (loss) before income taxes	28.6	32.0
Income tax expense (benefit)	5.0	6.4
Equity in net income (loss) of subsidiaries	0	0
Net income (loss)	23.6	25.6
Less: Net income attributable to noncontrolling interests	14.9	16.7
Net income (loss) attributable to AK Steel Holding Corporation	8.7	8.9
Other comprehensive income (loss)	0	(1.1)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	8.7	7.8
Current assets:
Cash and cash equivalents	15.5	39.4
Accounts receivable, net	68.5		61.1
Inventory, net	69.5		77.7
Deferred tax assets, current	0.2		0.2
Other current assets	3.8		2.3
Total current assets	157.5		169.8
Property, plant and equipment	622.1		613.5
Accumulated depreciation	(115.8)		(110.1)
Property, plant and equipment, net	506.3		503.4
Other non-current assets:
Investment in Magnetation LLC	186.5		187.8
Investment in affiliates	0		0
Inter-company accounts	919.8		896.7
Other non-current assets	124.8		123.6
TOTAL ASSETS	1,894.9		1,881.3
Current liabilities:
Accounts payable	52.7		51.9
Accrued liabilities	9.6		9.3
Current portion of long-term debt	0		0
Current portion of pension and other postretirement benefit obligations	0.5		0.5
Total current liabilities	62.8		61.7
Non-current liabilities:
Long-term debt	0		0
Pension and other postretirement benefit obligations	4.7		4.8
Other non-current liabilities	0.4		0.4
TOTAL LIABILITIES	67.9		66.9
Total stockholders' equity (deficit)	1,426.2		1,400.7
Noncontrolling interests	400.8		413.7
TOTAL EQUITY (DEFICIT)	1,827.0		1,814.4
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,894.9		1,881.3
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities	26.1	36.3
Cash flows from investing activities:
Capital investments	(6.3)	(2.9)
Other investing items, net	(0.2)	(0.8)
Net cash flows from investing activities	(6.5)	(3.7)
Cash flows from financing activities:
Net borrowings under credit facility	0
Redemption of long-term debt	0	0
Debt issuance costs	0	0
Purchase of treasury stock	0	0
Inter-company activity	(4.8)	(8.2)
SunCoke Middletown distributions to noncontrolling interest owners	(27.8)	(9.1)
Other financing items, net	0	0.7
Net cash flows from financing activities	(32.6)	(16.6)
Net increase (decrease) in cash and cash equivalents	(13.0)	16.0
Cash and cash equivalents, beginning of period	28.5	23.4
Cash and cash equivalents, end of period	15.5	39.4
Eliminations [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	(124.2)	(130.7)
Cost of products sold (exclusive of items shown separately below)	(117.2)	(121.7)
Selling and administrative expenses (exclusive of items shown separately below)	(10.6)	(10.2)
Depreciation	0	0
Pension and OPEB expense (income)	0	0
Total operating costs	(127.8)	(131.9)
Operating profit (loss)	3.6	1.2
Interest expense	0	0
Other income (expense)	0	0
Income (loss) before income taxes	3.6	1.2
Income tax expense (benefit)	1.4	0.5
Equity in net income (loss) of subsidiaries	73.6	(1.2)
Net income (loss)	75.8	(0.5)
Less: Net income attributable to noncontrolling interests	0	0
Net income (loss) attributable to AK Steel Holding Corporation	75.8	(0.5)
Other comprehensive income (loss)	24.2	20.8
Comprehensive income (loss) attributable to AK Steel Holding Corporation	100.0	20.3
Current assets:
Cash and cash equivalents	0	0
Accounts receivable, net	(22.4)		(28.3)
Inventory, net	(7.5)		(11.1)
Deferred tax assets, current	0		0
Other current assets	0		0
Total current assets	(29.9)		(39.4)
Property, plant and equipment	0		0
Accumulated depreciation	0		0
Property, plant and equipment, net	0		0
Other non-current assets:
Investment in Magnetation LLC	0		0
Investment in affiliates	1,492.3		1,378.6
Inter-company accounts	24.5		31.9
Other non-current assets	0		0
TOTAL ASSETS	1,486.9		1,371.1
Current liabilities:
Accounts payable	(0.7)		(0.6)
Accrued liabilities	0		0
Current portion of long-term debt	0		0
Current portion of pension and other postretirement benefit obligations	0		0
Total current liabilities	(0.7)		(0.6)
Non-current liabilities:
Long-term debt	0		0
Pension and other postretirement benefit obligations	0		0
Other non-current liabilities	0		0
TOTAL LIABILITIES	(0.7)		(0.6)
Total stockholders' equity (deficit)	1,487.6		1,371.7
Noncontrolling interests	0		0
TOTAL EQUITY (DEFICIT)	1,487.6		1,371.7
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,486.9		1,371.1
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities	(7.4)	(12.3)
Cash flows from investing activities:
Capital investments	0	0
Other investing items, net	0	0
Net cash flows from investing activities	0	0
Cash flows from financing activities:
Net borrowings under credit facility	0
Redemption of long-term debt	0	0
Debt issuance costs	0	0
Purchase of treasury stock	0	0
Inter-company activity	7.4	12.3
SunCoke Middletown distributions to noncontrolling interest owners	0	0
Other financing items, net	0	0
Net cash flows from financing activities	7.4	12.3
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	$ 0	$ 0
Senior Secured Notes Due December 2018 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	8.75%
Senior Notes Due May 2020 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.625%
Senior Notes Due April 2022 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	8.375%
Exchangeable Senior Notes Due November 2019 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.00%