Supplemental Guarantor Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	$ 1,404.5	$ 1,538.4	$ 2,774.3	$ 3,047.1
Cost of products sold (exclusive of items shown separately below)	1,309.2	1,392.4	2,561.5	2,801.4
Selling and administrative expenses (exclusive of items shown separately below)	50.2	50.8	101.8	106.6
Depreciation	47.9	48.4	96.5	96.7
Pension and OPEB expense (income)	(16.5)	(9.9)	(32.4)	(18.4)
Total operating costs	1,390.8	1,481.7	2,727.4	2,986.3
Operating profit (loss)	13.7	56.7	46.9	60.8
Interest expense	32.0	21.8	63.0	38.0
Other income (expense)	2.5	(4.7)	4.3	(3.8)
Income (loss) before income taxes	(15.8)	30.2	(11.8)	19.0
Income tax provision (benefit)	9.7	747.8	6.9	743.5
Equity in net income (loss) of subsidiaries	0	0	0	0
Net income (loss)	(25.5)	(717.6)	(18.7)	(724.5)
Less: Net income attributable to noncontrolling interests	14.9	6.6	31.6	11.5
Net income (loss) attributable to AK Steel Holding Corporation	(40.4)	(724.2)	(50.3)	(736.0)
Other comprehensive income (loss)	(28.9)	(4.6)	(48.6)	(16.7)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(69.3)	(728.8)	(98.9)	(752.7)
Current assets:
Cash and cash equivalents	58.4	37.4	58.4	37.4
Accounts receivable, net	515.8		515.8		473.9
Inventory, net	677.0		677.0		609.2
Deferred tax assets, current	74.9		74.9		73.2
Other current assets	30.1		30.1		59.4
Total current assets	1,356.2		1,356.2		1,442.7
Property, plant and equipment	5,966.7		5,966.7		5,943.9
Accumulated depreciation	(4,028.0)		(4,028.0)		(3,931.6)
Property, plant and equipment, net	1,938.7		1,938.7		2,012.3
Other non-current assets:
Investment in AFSG Holdings, Inc.	55.6		55.6		55.6
Investment in Magnetation LLC	193.8		193.8		150.0
Investment in affiliates	0		0		0
Inter-company accounts	0		0		0
Goodwill	37.1		37.1		37.1
Deferred tax assets, non-current	81.0		81.0		88.2
Other non-current assets	110.3		110.3		117.2
TOTAL ASSETS	3,772.7		3,772.7		3,903.1
Current liabilities:
Short-term borrowings under credit facility	40.0		40.0		0
Accounts payable	595.3		595.3		538.3
Accrued liabilities	141.7		141.7		164.8
Current portion of long-term debt	0.7		0.7		0.7
Current portion of pension and other postretirement benefit obligations	105.2		105.2		108.6
Total current liabilities	882.9		882.9		812.4
Non-current liabilities:
Long-term debt	1,414.7		1,414.7		1,411.2
Pension and other postretirement benefit obligations	1,548.1		1,548.1		1,661.7
Other non-current liabilities	108.0		108.0		108.8
TOTAL LIABILITIES	3,953.7		3,953.7		3,994.1
Total stockholders' equity (deficit)	(599.2)		(599.2)		(505.3)
Noncontrolling interests	418.2		418.2		414.3
TOTAL EQUITY (DEFICIT)	(181.0)	(360.6)	(181.0)	(360.6)	(91.0)	377.2
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,772.7		3,772.7		3,903.1
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(104.5)	(310.1)
Cash flows from investing activities:
Capital investments			(32.4)	(35.5)
Investments in acquired businesses			(50.0)	0
Other investing items, net			4.8	0.7
Net cash flows from investing activities			(77.6)	(34.8)
Cash flows from financing activities:
Net borrowings under credit facility			40.0	75.0
Proceeds from issuance of long-term debt			31.9	373.3
Redemption of long-term debt			(27.0)	(73.7)
Debt issuance costs			(2.4)	(8.4)
Purchase of treasury stock			(0.7)	(1.7)
Common stock dividends paid			0	(11.0)
Inter-company activity			0	0
SunCoke Middletown distributions to noncontrolling interest owners			(27.6)	(12.8)
Other financing items, net			(0.7)	(0.4)
Net cash flows from financing activities			13.5	340.3
Net increase (decrease) in cash and cash equivalents			(168.6)	(4.6)
Cash and cash equivalents, beginning of period			227.0	42.0
Cash and cash equivalents, end of period	58.4	37.4	58.4	37.4
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	1.3	2.5	2.7
Depreciation	0	0	0	0
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	1.0	1.3	2.5	2.7
Operating profit (loss)	(1.0)	(1.3)	(2.5)	(2.7)
Interest expense	0	0	0	0
Other income (expense)	0	0	0	0
Income (loss) before income taxes	(1.0)	(1.3)	(2.5)	(2.7)
Income tax provision (benefit)	0	0.6	0	0
Equity in net income (loss) of subsidiaries	(39.4)	(722.3)	(47.8)	(733.3)
Net income (loss)	(40.4)	(724.2)	(50.3)	(736.0)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(40.4)	(724.2)	(50.3)	(736.0)
Other comprehensive income (loss)	(28.9)	(4.6)	(48.6)	(16.7)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(69.3)	(728.8)	(98.9)	(752.7)
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		0.2
Total current assets	0.2		0.2		0.2
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 AFSG Holdings, Inc.	0		0		0
Investment in Magnetation LLC	0		0		0
Investment in affiliates	(2,799.8)		(2,799.8)		(2,660.7)
Inter-company accounts	2,200.4		2,200.4		2,155.2
Goodwill	0		0		0
Deferred tax assets, non-current	0		0		0
Other non-current assets	0		0		0
TOTAL ASSETS	(599.2)		(599.2)		(505.3)
Current liabilities:
Short-term borrowings under credit facility	0		0
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)	(599.2)		(599.2)		(505.3)
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	(599.2)		(599.2)		(505.3)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	(599.2)		(599.2)		(505.3)
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(2.1)	(2.2)
Cash flows from investing activities:
Capital investments			0	0
Investments in acquired businesses			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	0
Redemption of long-term debt			0	0
Debt issuance costs			0	0
Purchase of treasury stock			(0.7)	(1.7)
Common stock dividends paid				(11.0)
Inter-company activity			2.8	14.9
SunCoke Middletown distributions to noncontrolling interest owners			0	0
Other financing items, net			0	0
Net cash flows from financing activities			2.1	2.2
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	1,349.5	1,476.6	2,633.2	2,909.8
Cost of products sold (exclusive of items shown separately below)	1,282.2	1,366.3	2,482.4	2,729.8
Selling and administrative expenses (exclusive of items shown separately below)	50.8	51.9	101.4	109.2
Depreciation	43.0	43.7	86.7	87.3
Pension and OPEB expense (income)	(16.5)	(9.9)	(32.4)	(18.4)
Total operating costs	1,359.5	1,452.0	2,638.1	2,907.9
Operating profit (loss)	(10.0)	24.6	(4.9)	1.9
Interest expense	31.7	21.6	62.4	37.6
Other income (expense)	1.4	(2.7)	(0.7)	(5.3)
Income (loss) before income taxes	(40.3)	0.3	(68.0)	(41.0)
Income tax provision (benefit)	5.5	739.7	(4.2)	719.1
Equity in net income (loss) of subsidiaries	6.4	17.1	16.0	26.8
Net income (loss)	(39.4)	(722.3)	(47.8)	(733.3)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(39.4)	(722.3)	(47.8)	(733.3)
Other comprehensive income (loss)	(28.9)	(4.6)	(48.6)	(16.7)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(68.3)	(726.9)	(96.4)	(750.0)
Current assets:
Cash and cash equivalents	26.0	19.5	26.0	19.5
Accounts receivable, net	502.5		502.5		484.4
Inventory, net	599.1		599.1		504.2
Deferred tax assets, current	74.7		74.7		73.0
Other current assets	27.2		27.2		57.6
Total current assets	1,229.5		1,229.5		1,322.8
Property, plant and equipment	5,368.1		5,368.1		5,355.1
Accumulated depreciation	(3,928.6)		(3,928.6)		(3,841.9)
Property, plant and equipment, net	1,439.5		1,439.5		1,513.2
Other non-current assets:
Investment in AFSG Holdings, Inc.	0		0		0
Investment in Magnetation LLC	0		0		0
Investment in affiliates	1,363.2		1,363.2		1,337.4
Inter-company accounts	(3,092.6)		(3,092.6)		(3,066.5)
Goodwill	0		0		0
Deferred tax assets, non-current	80.6		80.6		87.9
Other non-current assets	71.0		71.0		79.8
TOTAL ASSETS	1,091.2		1,091.2		1,274.6
Current liabilities:
Short-term borrowings under credit facility	40.0		40.0
Accounts payable	544.4		544.4		494.8
Accrued liabilities	135.2		135.2		155.0
Current portion of long-term debt	0.7		0.7		0.7
Current portion of pension and other postretirement benefit obligations	104.7		104.7		108.1
Total current liabilities	825.0		825.0		758.6
Non-current liabilities:
Long-term debt	1,414.7		1,414.7		1,411.2
Pension and other postretirement benefit obligations	1,543.8		1,543.8		1,657.2
Other non-current liabilities	107.5		107.5		108.3
TOTAL LIABILITIES	3,891.0		3,891.0		3,935.3
Total stockholders' equity (deficit)	(2,799.8)		(2,799.8)		(2,660.7)
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	(2,799.8)		(2,799.8)		(2,660.7)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,091.2		1,091.2		1,274.6
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(167.8)	(362.4)
Cash flows from investing activities:
Capital investments			(22.5)	(16.4)
Investments in acquired businesses			(50.0)
Other investing items, net			5.1	0.8
Net cash flows from investing activities			(67.4)	(15.6)
Cash flows from financing activities:
Net borrowings under credit facility			40.0	75.0
Proceeds from issuance of long-term debt			31.9	373.3
Redemption of long-term debt			(27.0)	(73.7)
Debt issuance costs			(2.4)	(8.4)
Purchase of treasury stock			0	0
Common stock dividends paid				0
Inter-company activity			15.2	11.4
SunCoke Middletown distributions to noncontrolling interest owners			0	0
Other financing items, net			(0.1)	0
Net cash flows from financing activities			57.6	377.6
Net increase (decrease) in cash and cash equivalents			(177.6)	(0.4)
Cash and cash equivalents, beginning of period			203.6	19.9
Cash and cash equivalents, end of period	26.0	19.5	26.0	19.5
Other Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	209.5	243.6	426.3	480.6
Cost of products sold (exclusive of items shown separately below)	170.8	199.3	344.6	395.7
Selling and administrative expenses (exclusive of items shown separately below)	8.8	9.1	18.5	17.4
Depreciation	4.9	4.7	9.8	9.4
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	184.5	213.1	372.9	422.5
Operating profit (loss)	25.0	30.5	53.4	58.1
Interest expense	0.3	0.2	0.6	0.4
Other income (expense)	1.1	(2.0)	5.0	1.5
Income (loss) before income taxes	25.8	28.3	57.8	59.2
Income tax provision (benefit)	4.3	6.3	10.7	23.0
Equity in net income (loss) of subsidiaries	0	0	0	0
Net income (loss)	21.5	22.0	47.1	36.2
Less: Net income attributable to noncontrolling interests	14.9	6.6	31.6	11.5
Net income (loss) attributable to AK Steel Holding Corporation	6.6	15.4	15.5	24.7
Other comprehensive income (loss)	0.4	(1.2)	(0.7)	(0.4)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	7.0	14.2	14.8	24.3
Current assets:
Cash and cash equivalents	32.4	17.9	32.4	17.9
Accounts receivable, net	67.9		67.9		54.3
Inventory, net	86.3		86.3		114.4
Deferred tax assets, current	0.2		0.2		0.2
Other current assets	2.7		2.7		1.6
Total current assets	189.5		189.5		193.9
Property, plant and equipment	598.6		598.6		588.8
Accumulated depreciation	(99.4)		(99.4)		(89.7)
Property, plant and equipment, net	499.2		499.2		499.1
Other non-current assets:
Investment in AFSG Holdings, Inc.	55.6		55.6		55.6
Investment in Magnetation LLC	193.8		193.8		150.0
Investment in affiliates	0		0		0
Inter-company accounts	836.7		836.7		843.8
Goodwill	37.1		37.1		37.1
Deferred tax assets, non-current	0.4		0.4		0.3
Other non-current assets	39.3		39.3		37.4
TOTAL ASSETS	1,851.6		1,851.6		1,817.2
Current liabilities:
Short-term borrowings under credit facility	0		0
Accounts payable	52.5		52.5		44.4
Accrued liabilities	7.2		7.2		9.8
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	60.2		60.2		54.7
Non-current liabilities:
Long-term debt	0		0		0
Pension and other postretirement benefit obligations	4.3		4.3		4.5
Other non-current liabilities	0.5		0.5		0.5
TOTAL LIABILITIES	65.0		65.0		59.7
Total stockholders' equity (deficit)	1,368.4		1,368.4		1,343.2
Noncontrolling interests	418.2		418.2		414.3
TOTAL EQUITY (DEFICIT)	1,786.6		1,786.6		1,757.5
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,851.6		1,851.6		1,817.2
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			77.5	55.7
Cash flows from investing activities:
Capital investments			(9.9)	(19.1)
Investments in acquired businesses			0
Other investing items, net			(0.3)	(0.1)
Net cash flows from investing activities			(10.2)	(19.2)
Cash flows from financing activities:
Net borrowings under credit facility			0	0
Proceeds from issuance of long-term debt			0	0
Redemption of long-term debt			0	0
Debt issuance costs			0	0
Purchase of treasury stock			0	0
Common stock dividends paid				0
Inter-company activity			(30.1)	(27.5)
SunCoke Middletown distributions to noncontrolling interest owners			(27.6)	(12.8)
Other financing items, net			(0.6)	(0.4)
Net cash flows from financing activities			(58.3)	(40.7)
Net increase (decrease) in cash and cash equivalents			9.0	(4.2)
Cash and cash equivalents, beginning of period			23.4	22.1
Cash and cash equivalents, end of period	32.4	17.9	32.4	17.9
Eliminations [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	(154.5)	(181.8)	(285.2)	(343.3)
Cost of products sold (exclusive of items shown separately below)	(143.8)	(173.2)	(265.5)	(324.1)
Selling and administrative expenses (exclusive of items shown separately below)	(10.4)	(11.5)	(20.6)	(22.7)
Depreciation	0	0	0	0
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	(154.2)	(184.7)	(286.1)	(346.8)
Operating profit (loss)	(0.3)	2.9	0.9	3.5
Interest expense	0	0	0	0
Other income (expense)	0	0	0	0
Income (loss) before income taxes	(0.3)	2.9	0.9	3.5
Income tax provision (benefit)	(0.1)	1.2	0.4	1.4
Equity in net income (loss) of subsidiaries	33.0	705.2	31.8	706.5
Net income (loss)	32.8	706.9	32.3	708.6
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	32.8	706.9	32.3	708.6
Other comprehensive income (loss)	28.5	5.8	49.3	17.1
Comprehensive income (loss) attributable to AK Steel Holding Corporation	61.3	712.7	81.6	725.7
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	(54.6)		(54.6)		(64.8)
Inventory, net	(8.4)		(8.4)		(9.4)
Deferred tax assets, current	0		0		0
Other current assets	0		0		0
Total current assets	(63.0)		(63.0)		(74.2)
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 AFSG Holdings, Inc.	0		0		0
Investment in Magnetation LLC	0		0		0
Investment in affiliates	1,436.6		1,436.6		1,323.3
Inter-company accounts	55.5		55.5		67.5
Goodwill	0		0		0
Deferred tax assets, non-current	0		0		0
Other non-current assets	0		0		0
TOTAL ASSETS	1,429.1		1,429.1		1,316.6
Current liabilities:
Short-term borrowings under credit facility	0		0
Accounts payable	(1.6)		(1.6)		(0.9)
Accrued liabilities	(0.7)		(0.7)		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	(2.3)		(2.3)		(0.9)
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	(2.3)		(2.3)		(0.9)
Total stockholders' equity (deficit)	1,431.4		1,431.4		1,317.5
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	1,431.4		1,431.4		1,317.5
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,429.1		1,429.1		1,316.6
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(12.1)	(1.2)
Cash flows from investing activities:
Capital investments			0	0
Investments in acquired businesses			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	0
Redemption of long-term debt			0	0
Debt issuance costs			0	0
Purchase of treasury stock			0	0
Common stock dividends paid				0
Inter-company activity			12.1	1.2
SunCoke Middletown distributions to noncontrolling interest owners			0	0
Other financing items, net			0	0
Net cash flows from financing activities			12.1	1.2
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