Supplemental Guarantor Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	$ 1,530.8	$ 1,404.5	$ 2,914.3	$ 2,774.3
Cost of products sold (exclusive of items shown separately below)	1,416.9	1,309.2	2,752.5	2,561.5
Selling and administrative expenses (exclusive of items shown separately below)	53.9	50.2	114.1	101.8
Depreciation	48.5	47.9	97.2	96.5
Pension and OPEB expense (income)	(25.0)	(16.5)	(50.7)	(32.4)
Total operating costs	1,494.3	1,390.8	2,913.1	2,727.4
Operating profit (loss)	36.5	13.7	1.2	46.9
Interest expense	33.2	32.0	65.4	63.0
Other income (expense)	(3.0)	2.5	(4.9)	4.3
Income (loss) before income taxes	0.3	(15.8)	(69.1)	(11.8)
Income tax expense (benefit)	1.8	9.7	3.6	6.9
Equity in net income (loss) of subsidiaries	0	0	0	0
Net income (loss)	(1.5)	(25.5)	(72.7)	(18.7)
Less: Net income attributable to noncontrolling interests	15.6	14.9	30.5	31.6
Net income (loss) attributable to AK Steel Holding Corporation	(17.1)	(40.4)	(103.2)	(50.3)
Other comprehensive income (loss)	(27.2)	(28.9)	(51.4)	(48.6)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(44.3)	(69.3)	(154.6)	(98.9)
Current assets:
Cash and cash equivalents	54.8	58.4	54.8	58.4
Accounts receivable, net	596.2		596.2		525.2
Inventory, net	738.3		738.3		586.6
Deferred tax assets, current	63.9		63.9		69.6
Other current assets	52.8		52.8		46.5
Total current assets	1,506.0		1,506.0		1,273.2
Property, plant and equipment	5,893.6		5,893.6		5,871.9
Accumulated depreciation	(4,088.3)		(4,088.3)		(3,991.8)
Property, plant and equipment, net	1,805.3		1,805.3		1,880.1
Other non-current assets:
Investment in Magnetation LLC	229.0		229.0		187.8
Investment in affiliates	0		0		0
Inter-company accounts	0		0		0
Other non-current assets	266.3		266.3		264.6
TOTAL ASSETS	3,806.6		3,806.6		3,605.7
Current liabilities:
Accounts payable	642.4		642.4		601.8
Accrued liabilities	170.2		170.2		142.9
Current portion of long-term debt	0.4		0.4		0.8
Current portion of pension and other postretirement benefit obligations	69.5		69.5		85.9
Total current liabilities	882.5		882.5		831.4
Non-current liabilities:
Long-term debt	1,948.2		1,948.2		1,506.2
Pension and other postretirement benefit obligations	816.3		816.3		965.4
Other non-current liabilities	115.3		115.3		110.0
TOTAL LIABILITIES	3,762.3		3,762.3		3,413.0
Total stockholders' equity (deficit)	(371.0)		(371.0)		(221.0)
Noncontrolling interests	415.3		415.3		413.7
TOTAL EQUITY (DEFICIT)	44.3	(181.0)	44.3	(181.0)	192.7	(91.0)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,806.6		3,806.6		3,605.7
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(331.1)	(104.5)
Cash flows from investing activities:
Capital investments			(27.6)	(32.4)
Investments in acquired businesses			(45.0)	(50.0)
Other investing items, net			6.9	4.8
Net cash flows from investing activities			(65.7)	(77.6)
Cash flows from financing activities:
Net borrowings under credit facility			440.0	40.0
Proceeds from issuance of long-term debt			0	31.9
Redemption of long-term debt			(0.4)	(27.0)
Debt issuance costs			(3.3)	(2.4)
Inter-company activity			0	0
SunCoke Middletown distributions to noncontrolling interest owners			(28.9)	(27.6)
Other financing items, net			(1.1)	(1.4)
Net cash flows from financing activities			406.3	13.5
Net increase (decrease) in cash and cash equivalents			9.5	(168.6)
Cash and cash equivalents, beginning of period			45.3	227.0
Cash and cash equivalents, end of period	54.8	58.4	54.8	58.4
AK Holding [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	0	0	0	0
Cost of products sold (exclusive of items shown separately below)	0	0	0	0
Selling and administrative expenses (exclusive of items shown separately below)	1.0	1.0	2.6	2.5
Depreciation	0	0	0	0
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	1.0	1.0	2.6	2.5
Operating profit (loss)	(1.0)	(1.0)	(2.6)	(2.5)
Interest expense	0	0	0	0
Other income (expense)	0	0	0	0
Income (loss) before income taxes	(1.0)	(1.0)	(2.6)	(2.5)
Income tax expense (benefit)	0	0	0	0
Equity in net income (loss) of subsidiaries	(16.1)	(39.4)	(100.6)	(47.8)
Net income (loss)	(17.1)	(40.4)	(103.2)	(50.3)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(17.1)	(40.4)	(103.2)	(50.3)
Other comprehensive income (loss)	(27.2)	(28.9)	(51.4)	(48.6)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(44.3)	(69.3)	(154.6)	(98.9)
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0		0		0
Inventory, net	0		0		0
Deferred tax assets, current	0		0		0
Other current assets	0.2		0.2		0.3
Total current assets	0.2		0.2		0.3
Property, plant and equipment	0		0		0
Accumulated depreciation	0		0		0
Property, plant and equipment, net	0		0		0
Other non-current assets:
Investment in Magnetation LLC	0		0		0
Investment in affiliates	(2,940.0)		(2,940.0)		(2,772.4)
Inter-company accounts	2,568.8		2,568.8		2,551.1
Other non-current assets	0		0		0
TOTAL ASSETS	(371.0)		(371.0)		(221.0)
Current liabilities:
Accounts payable	0		0		0
Accrued liabilities	0		0		0
Current portion of long-term debt	0		0		0
Current portion of pension and other postretirement benefit obligations	0		0		0
Total current liabilities	0		0		0
Non-current liabilities:
Long-term debt	0		0		0
Pension and other postretirement benefit obligations	0		0		0
Other non-current liabilities	0		0		0
TOTAL LIABILITIES	0		0		0
Total stockholders' equity (deficit)	(371.0)		(371.0)		(221.0)
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	(371.0)		(371.0)		(221.0)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	(371.0)		(371.0)		(221.0)
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(2.0)	(2.1)
Cash flows from investing activities:
Capital investments			0	0
Investments in acquired businesses			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	0
Proceeds from issuance of long-term debt				0
Redemption of long-term debt			0	0
Debt issuance costs			0	0
Inter-company activity			3.0	2.8
SunCoke Middletown distributions to noncontrolling interest owners			0	0
Other financing items, net			(1.0)	(0.7)
Net cash flows from financing activities			2.0	2.1
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	0	0
AK Steel [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	1,483.1	1,349.5	2,798.2	2,633.2
Cost of products sold (exclusive of items shown separately below)	1,404.1	1,282.2	2,708.0	2,482.4
Selling and administrative expenses (exclusive of items shown separately below)	53.8	50.8	112.7	101.4
Depreciation	42.3	43.0	84.8	86.7
Pension and OPEB expense (income)	(25.0)	(16.5)	(50.7)	(32.4)
Total operating costs	1,475.2	1,359.5	2,854.8	2,638.1
Operating profit (loss)	7.9	(10.0)	(56.6)	(4.9)
Interest expense	32.5	31.7	64.2	62.4
Other income (expense)	(3.9)	1.4	(7.7)	(0.7)
Income (loss) before income taxes	(28.5)	(40.3)	(128.5)	(68.0)
Income tax expense (benefit)	(4.7)	5.5	(9.3)	(4.2)
Equity in net income (loss) of subsidiaries	7.7	6.4	18.6	16.0
Net income (loss)	(16.1)	(39.4)	(100.6)	(47.8)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(16.1)	(39.4)	(100.6)	(47.8)
Other comprehensive income (loss)	(27.2)	(28.9)	(51.4)	(48.6)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(43.3)	(68.3)	(152.0)	(96.4)
Current assets:
Cash and cash equivalents	19.0	26.0	19.0	26.0
Accounts receivable, net	554.5		554.5		492.4
Inventory, net	667.6		667.6		520.0
Deferred tax assets, current	63.7		63.7		69.4
Other current assets	49.6		49.6		43.9
Total current assets	1,354.4		1,354.4		1,142.5
Property, plant and equipment	5,269.5		5,269.5		5,258.4
Accumulated depreciation	(3,966.6)		(3,966.6)		(3,881.7)
Property, plant and equipment, net	1,302.9		1,302.9		1,376.7
Other non-current assets:
Investment in Magnetation LLC	0		0		0
Investment in affiliates	1,429.7		1,429.7		1,393.8
Inter-company accounts	(3,471.7)		(3,471.7)		(3,479.7)
Other non-current assets	140.0		140.0		141.0
TOTAL ASSETS	755.3		755.3		574.3
Current liabilities:
Accounts payable	591.7		591.7		550.5
Accrued liabilities	159.4		159.4		133.6
Current portion of long-term debt	0.4		0.4		0.8
Current portion of pension and other postretirement benefit obligations	69.0		69.0		85.4
Total current liabilities	820.5		820.5		770.3
Non-current liabilities:
Long-term debt	1,948.2		1,948.2		1,506.2
Pension and other postretirement benefit obligations	811.8		811.8		960.6
Other non-current liabilities	114.8		114.8		109.6
TOTAL LIABILITIES	3,695.3		3,695.3		3,346.7
Total stockholders' equity (deficit)	(2,940.0)		(2,940.0)		(2,772.4)
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	(2,940.0)		(2,940.0)		(2,772.4)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	755.3		755.3		574.3
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(375.3)	(167.8)
Cash flows from investing activities:
Capital investments			(16.7)	(22.5)
Investments in acquired businesses			0	0
Other investing items, net			7.2	5.1
Net cash flows from investing activities			(9.5)	(17.4)
Cash flows from financing activities:
Net borrowings under credit facility			440.0	40.0
Proceeds from issuance of long-term debt				31.9
Redemption of long-term debt			(0.4)	(27.0)
Debt issuance costs			(3.3)	(2.4)
Inter-company activity			(49.2)	(34.8)
SunCoke Middletown distributions to noncontrolling interest owners			0	0
Other financing items, net			(0.1)	(0.1)
Net cash flows from financing activities			387.0	7.6
Net increase (decrease) in cash and cash equivalents			2.2	(177.6)
Cash and cash equivalents, beginning of period			16.8	203.6
Cash and cash equivalents, end of period	19.0	26.0	19.0	26.0
Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	72.3	66.4	140.1	133.6
Cost of products sold (exclusive of items shown separately below)	51.9	47.9	101.5	96.3
Selling and administrative expenses (exclusive of items shown separately below)	2.9	2.7	5.7	5.3
Depreciation	1.0	1.1	2.0	2.2
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	55.8	51.7	109.2	103.8
Operating profit (loss)	16.5	14.7	30.9	29.8
Interest expense	0	0	0	0
Other income (expense)	1.7	1.4	3.3	3.1
Income (loss) before income taxes	18.2	16.1	34.2	32.9
Income tax expense (benefit)	7.9	10.7	13.7	13.2
Equity in net income (loss) of subsidiaries	0	0	0	0
Net income (loss)	10.3	5.4	20.5	19.7
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	10.3	5.4	20.5	19.7
Other comprehensive income (loss)	0	0	0	0
Comprehensive income (loss) attributable to AK Steel Holding Corporation	10.3	5.4	20.5	19.7
Current assets:
Cash and cash equivalents	0.2	0	0.2	0
Accounts receivable, net	32.1		32.1		25.2
Inventory, net	26.0		26.0		19.2
Deferred tax assets, current	0		0		0
Other current assets	0.3		0.3		0.2
Total current assets	58.6		58.6		44.6
Property, plant and equipment	95.4		95.4		94.9
Accumulated depreciation	(69.9)		(69.9)		(67.9)
Property, plant and equipment, net	25.5		25.5		27.0
Other non-current assets:
Investment in Magnetation LLC	0		0		0
Investment in affiliates	0		0		0
Inter-company accounts	1,303.7		1,303.7		1,269.6
Other non-current assets	33.0		33.0		33.0
TOTAL ASSETS	1,420.8		1,420.8		1,374.2
Current liabilities:
Accounts payable	12.6		12.6		6.3
Accrued liabilities	2.7		2.7		2.9
Current portion of long-term debt	0		0		0
Current portion of pension and other postretirement benefit obligations	0		0		0
Total current liabilities	15.3		15.3		9.2
Non-current liabilities:
Long-term debt	0		0		0
Pension and other postretirement benefit obligations	0		0		0
Other non-current liabilities	0		0		0
TOTAL LIABILITIES	15.3		15.3		9.2
Total stockholders' equity (deficit)	1,405.5		1,405.5		1,365.0
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	1,405.5		1,405.5		1,365.0
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,420.8		1,420.8		1,374.2
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			15.6	22.1
Cash flows from investing activities:
Capital investments			(1.3)	(0.2)
Investments in acquired businesses			0	0
Other investing items, net			0	(0.4)
Net cash flows from investing activities			(1.3)	(0.6)
Cash flows from financing activities:
Net borrowings under credit facility			0	0
Proceeds from issuance of long-term debt				0
Redemption of long-term debt			0	0
Debt issuance costs			0	0
Inter-company activity			(14.1)	(21.5)
SunCoke Middletown distributions to noncontrolling interest owners			0	0
Other financing items, net			0	0
Net cash flows from financing activities			(14.1)	(21.5)
Net increase (decrease) in cash and cash equivalents			0.2	0
Cash and cash equivalents, beginning of period			0	0
Cash and cash equivalents, end of period	0.2	0	0.2	0
Other Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	133.2	143.1	258.0	292.7
Cost of products sold (exclusive of items shown separately below)	105.3	122.9	204.6	248.3
Selling and administrative expenses (exclusive of items shown separately below)	7.1	6.1	14.6	13.2
Depreciation	5.2	3.8	10.4	7.6
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	117.6	132.8	229.6	269.1
Operating profit (loss)	15.6	10.3	28.4	23.6
Interest expense	0.7	0.3	1.2	0.6
Other income (expense)	(0.8)	(0.3)	(0.5)	1.9
Income (loss) before income taxes	14.1	9.7	26.7	24.9
Income tax expense (benefit)	(0.4)	(6.4)	(1.2)	(2.5)
Equity in net income (loss) of subsidiaries	0	0	0	0
Net income (loss)	14.5	16.1	27.9	27.4
Less: Net income attributable to noncontrolling interests	15.6	14.9	30.5	31.6
Net income (loss) attributable to AK Steel Holding Corporation	(1.1)	1.2	(2.6)	(4.2)
Other comprehensive income (loss)	(0.1)	0.4	(0.1)	(0.7)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(1.2)	1.6	(2.7)	(4.9)
Current assets:
Cash and cash equivalents	35.6	32.4	35.6	32.4
Accounts receivable, net	42.0		42.0		35.9
Inventory, net	54.7		54.7		58.5
Deferred tax assets, current	0.2		0.2		0.2
Other current assets	2.7		2.7		2.1
Total current assets	135.2		135.2		125.2
Property, plant and equipment	528.7		528.7		518.6
Accumulated depreciation	(51.8)		(51.8)		(42.2)
Property, plant and equipment, net	476.9		476.9		476.4
Other non-current assets:
Investment in Magnetation LLC	229.0		229.0		187.8
Investment in affiliates	0		0		0
Inter-company accounts	(437.0)		(437.0)		(372.9)
Other non-current assets	93.3		93.3		90.6
TOTAL ASSETS	497.4		497.4		507.1
Current liabilities:
Accounts payable	38.1		38.1		45.6
Accrued liabilities	8.1		8.1		6.4
Current portion of long-term debt	0		0		0
Current portion of pension and other postretirement benefit obligations	0.5		0.5		0.5
Total current liabilities	46.7		46.7		52.5
Non-current liabilities:
Long-term debt	0		0		0
Pension and other postretirement benefit obligations	4.5		4.5		4.8
Other non-current liabilities	0.5		0.5		0.4
TOTAL LIABILITIES	51.7		51.7		57.7
Total stockholders' equity (deficit)	30.4		30.4		35.7
Noncontrolling interests	415.3		415.3		413.7
TOTAL EQUITY (DEFICIT)	445.7		445.7		449.4
TOTAL LIABILITIES AND EQUITY (DEFICIT)	497.4		497.4		507.1
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			26.3	55.4
Cash flows from investing activities:
Capital investments			(9.6)	(9.7)
Investments in acquired businesses			(45.0)	(50.0)
Other investing items, net			(0.3)	0.1
Net cash flows from investing activities			(54.9)	(59.6)
Cash flows from financing activities:
Net borrowings under credit facility			0	0
Proceeds from issuance of long-term debt				0
Redemption of long-term debt			0	0
Debt issuance costs			0	0
Inter-company activity			64.6	41.4
SunCoke Middletown distributions to noncontrolling interest owners			(28.9)	(27.6)
Other financing items, net			0	(0.6)
Net cash flows from financing activities			35.7	13.2
Net increase (decrease) in cash and cash equivalents			7.1	9.0
Cash and cash equivalents, beginning of period			28.5	23.4
Cash and cash equivalents, end of period	35.6	32.4	35.6	32.4
Eliminations [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	(157.8)	(154.5)	(282.0)	(285.2)
Cost of products sold (exclusive of items shown separately below)	(144.4)	(143.8)	(261.6)	(265.5)
Selling and administrative expenses (exclusive of items shown separately below)	(10.9)	(10.4)	(21.5)	(20.6)
Depreciation	0	0	0	0
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	(155.3)	(154.2)	(283.1)	(286.1)
Operating profit (loss)	(2.5)	(0.3)	1.1	0.9
Interest expense	0	0	0	0
Other income (expense)	0	0	0	0
Income (loss) before income taxes	(2.5)	(0.3)	1.1	0.9
Income tax expense (benefit)	(1.0)	(0.1)	0.4	0.4
Equity in net income (loss) of subsidiaries	8.4	33.0	82.0	31.8
Net income (loss)	6.9	32.8	82.7	32.3
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	6.9	32.8	82.7	32.3
Other comprehensive income (loss)	27.3	28.5	51.5	49.3
Comprehensive income (loss) attributable to AK Steel Holding Corporation	34.2	61.3	134.2	81.6
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	(32.4)		(32.4)		(28.3)
Inventory, net	(10.0)		(10.0)		(11.1)
Deferred tax assets, current	0		0		0
Other current assets	0		0		0
Total current assets	(42.4)		(42.4)		(39.4)
Property, plant and equipment	0		0		0
Accumulated depreciation	0		0		0
Property, plant and equipment, net	0		0		0
Other non-current assets:
Investment in Magnetation LLC	0		0		0
Investment in affiliates	1,510.3		1,510.3		1,378.6
Inter-company accounts	36.2		36.2		31.9
Other non-current assets	0		0		0
TOTAL ASSETS	1,504.1		1,504.1		1,371.1
Current liabilities:
Accounts payable	0		0		(0.6)
Accrued liabilities	0		0		0
Current portion of long-term debt	0		0		0
Current portion of pension and other postretirement benefit obligations	0		0		0
Total current liabilities	0		0		(0.6)
Non-current liabilities:
Long-term debt	0		0		0
Pension and other postretirement benefit obligations	0		0		0
Other non-current liabilities	0		0		0
TOTAL LIABILITIES	0		0		(0.6)
Total stockholders' equity (deficit)	1,504.1		1,504.1		1,371.7
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	1,504.1		1,504.1		1,371.7
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,504.1		1,504.1		1,371.1
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			4.3	(12.1)
Cash flows from investing activities:
Capital investments			0	0
Investments in acquired businesses			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	0
Proceeds from issuance of long-term debt				0
Redemption of long-term debt			0	0
Debt issuance costs			0	0
Inter-company activity			(4.3)	12.1
SunCoke Middletown distributions to noncontrolling interest owners			0	0
Other financing items, net			0	0
Net cash flows from financing activities			(4.3)	12.1
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	$ 0	$ 0
Senior Secured Notes Due December 2018 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	8.75%		8.75%		8.75%
Senior Notes Due May 2020 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.625%		7.625%		7.625%
Senior Notes Due April 2022 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	8.375%		8.375%		8.375%
Exchangeable Senior Notes Due November 2019 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.00%		5.00%		5.00%