Supplemental Guarantor Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	$ 1,331.3	$ 1,463.5	$ 4,105.6	$ 4,510.6
Cost of products sold (exclusive of items shown separately below)	1,222.4	1,385.0	3,783.9	4,186.4
Selling and administrative expenses (exclusive of items shown separately below)	51.5	51.9	153.3	158.5
Depreciation	48.4	48.2	144.9	144.9
Pension and OPEB expense (income)	(16.9)	(9.6)	(49.3)	(28.0)
Total operating costs	1,305.4	1,475.5	4,032.8	4,461.8
Operating profit (loss)	25.9	(12.0)	72.8	48.8
Interest expense	32.1	22.4	95.1	60.4
Other income (expense)	(2.8)	5.7	1.5	1.9
Income (loss) before income taxes	(9.0)	(28.7)	(20.8)	(9.7)
Income tax provision (benefit)	6.7	23.8	13.6	767.3
Equity in net income (loss) of subsidiaries	0	0	0	0
Net income (loss)	(15.7)	(52.5)	(34.4)	(777.0)
Less: Net income attributable to noncontrolling interests	16.0	8.4	47.6	19.9
Net income (loss) attributable to AK Steel Holding Corporation	(31.7)	(60.9)	(82.0)	(796.9)
Other comprehensive income (loss)	(3.4)	(8.2)	(52.0)	(24.9)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(35.1)	(69.1)	(134.0)	(821.8)
Current assets:
Cash and cash equivalents	65.7	47.1	65.7	47.1
Accounts receivable, net	536.6		536.6		473.9
Inventory, net	684.6		684.6		609.2
Deferred tax assets, current	70.8		70.8		73.2
Other current assets	44.8		44.8		59.4
Total current assets	1,402.5		1,402.5		1,442.7
Property, plant and equipment	5,974.0		5,974.0		5,943.9
Accumulated depreciation	(4,068.3)		(4,068.3)		(3,931.6)
Property, plant and equipment, net	1,905.7		1,905.7		2,012.3
Other non-current assets:
Investment in AFSG Holdings, Inc.	55.6		55.6		55.6
Investment in Magnetation LLC	190.4		190.4		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	79.6		79.6		88.2
Other non-current assets	95.5		95.5		117.2
TOTAL ASSETS	3,766.4		3,766.4		3,903.1
Current liabilities:
Short-term borrowings under credit facility	185.0		185.0		0
Accounts payable	563.9		563.9		538.3
Accrued liabilities	179.1		179.1		164.8
Current portion of long-term debt	0.7		0.7		0.7
Current portion of pension and other postretirement benefit obligations	78.9		78.9		108.6
Total current liabilities	1,007.6		1,007.6		812.4
Non-current liabilities:
Long-term debt	1,415.4		1,415.4		1,411.2
Pension and other postretirement benefit obligations	1,447.1		1,447.1		1,661.7
Other non-current liabilities	108.1		108.1		108.8
TOTAL LIABILITIES	3,978.2		3,978.2		3,994.1
Total stockholders' equity (deficit)	(632.6)		(632.6)		(505.3)
Noncontrolling interests	420.8		420.8		414.3
TOTAL EQUITY (DEFICIT)	(211.8)	(413.9)	(211.8)	(413.9)	(91.0)	377.2
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,766.4		3,766.4		3,903.1
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(223.7)	(387.9)
Cash flows from investing activities:
Capital investments			(48.1)	(49.3)
Investments in acquired businesses			(50.0)	(38.1)
Other investing items, net			15.1	4.6
Net cash flows from investing activities			(83.0)	(82.8)
Cash flows from financing activities:
Net borrowings under credit facility			185.0	192.0
Proceeds from issuance of long-term debt			31.9	373.3
Redemption of long-term debt			(27.2)	(73.9)
Debt issuance costs			(3.1)	(8.6)
Purchase of treasury stock			(0.7)	(1.7)
Common stock dividends paid			0	(11.0)
Inter-company activity			0	0
SunCoke Middletown advances from (distributions to) noncontrolling interest owners			(41.1)	5.5
Other financing items, net			0.6	0.2
Net cash flows from financing activities			145.4	475.8
Net increase (decrease) in cash and cash equivalents			(161.3)	5.1
Cash and cash equivalents, beginning of period			227.0	42.0
Cash and cash equivalents, end of period	65.7	47.1	65.7	47.1
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	0.9	3.5	3.6
Depreciation	0	0	0	0
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	1.0	0.9	3.5	3.6
Operating profit (loss)	(1.0)	(0.9)	(3.5)	(3.6)
Interest expense	0	0	0	0
Other income (expense)	0	0	0	0
Income (loss) before income taxes	(1.0)	(0.9)	(3.5)	(3.6)
Income tax provision (benefit)	0	0	0	0
Equity in net income (loss) of subsidiaries	(30.7)	(60.0)	(78.5)	(793.3)
Net income (loss)	(31.7)	(60.9)	(82.0)	(796.9)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(31.7)	(60.9)	(82.0)	(796.9)
Other comprehensive income (loss)	(3.4)	(8.2)	(52.0)	(24.9)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(35.1)	(69.1)	(134.0)	(821.8)
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	(2,814.9)		(2,814.9)		(2,660.7)
Inter-company accounts	2,182.1		2,182.1		2,155.2
Goodwill	0		0		0
Deferred tax assets, non-current	0		0		0
Other non-current assets	0		0		0
TOTAL ASSETS	(632.6)		(632.6)		(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)	(632.6)		(632.6)		(505.3)
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	(632.6)		(632.6)		(505.3)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	(632.6)		(632.6)		(505.3)
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(2.8)	(2.9)
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	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			3.5	15.6
SunCoke Middletown advances from (distributions to) noncontrolling interest owners			0	0
Other financing items, net			0	0
Net cash flows from financing activities			2.8	2.9
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	1,284.1	1,409.2	3,917.3	4,319.0
Cost of products sold (exclusive of items shown separately below)	1,206.4	1,365.9	3,688.8	4,095.7
Selling and administrative expenses (exclusive of items shown separately below)	50.8	52.5	152.2	161.7
Depreciation	43.1	43.3	129.8	130.6
Pension and OPEB expense (income)	(16.9)	(9.6)	(49.3)	(28.0)
Total operating costs	1,283.4	1,452.1	3,921.5	4,360.0
Operating profit (loss)	0.7	(42.9)	(4.2)	(41.0)
Interest expense	31.7	22.2	94.1	59.8
Other income (expense)	(1.9)	(2.1)	(2.6)	(7.4)
Income (loss) before income taxes	(32.9)	(67.2)	(100.9)	(108.2)
Income tax provision (benefit)	3.6	8.5	(0.6)	727.6
Equity in net income (loss) of subsidiaries	5.8	15.7	21.8	42.5
Net income (loss)	(30.7)	(60.0)	(78.5)	(793.3)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(30.7)	(60.0)	(78.5)	(793.3)
Other comprehensive income (loss)	(3.4)	(8.2)	(52.0)	(24.9)
Comprehensive income (loss) attributable to AK Steel Holding Corporation	(34.1)	(68.2)	(130.5)	(818.2)
Current assets:
Cash and cash equivalents	28.1	27.3	28.1	27.3
Accounts receivable, net	528.3		528.3		484.4
Inventory, net	596.3		596.3		504.2
Deferred tax assets, current	70.6		70.6		73.0
Other current assets	41.3		41.3		57.6
Total current assets	1,264.6		1,264.6		1,322.8
Property, plant and equipment	5,368.2		5,368.2		5,355.1
Accumulated depreciation	(3,963.6)		(3,963.6)		(3,841.9)
Property, plant and equipment, net	1,404.6		1,404.6		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	1,359.4		1,359.4		1,337.4
Inter-company accounts	(3,075.3)		(3,075.3)		(3,066.5)
Goodwill	0		0		0
Deferred tax assets, non-current	79.3		79.3		87.9
Other non-current assets	65.7		65.7		79.8
TOTAL ASSETS	1,098.3		1,098.3		1,274.6
Current liabilities:
Short-term borrowings under credit facility	185.0		185.0
Accounts payable	514.4		514.4		494.8
Accrued liabilities	169.0		169.0		155.0
Current portion of long-term debt	0.7		0.7		0.7
Current portion of pension and other postretirement benefit obligations	78.4		78.4		108.1
Total current liabilities	947.5		947.5		758.6
Non-current liabilities:
Long-term debt	1,415.4		1,415.4		1,411.2
Pension and other postretirement benefit obligations	1,442.8		1,442.8		1,657.2
Other non-current liabilities	107.5		107.5		108.3
TOTAL LIABILITIES	3,913.2		3,913.2		3,935.3
Total stockholders' equity (deficit)	(2,814.9)		(2,814.9)		(2,660.7)
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	(2,814.9)		(2,814.9)		(2,660.7)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,098.3		1,098.3		1,274.6
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(325.4)	(431.6)
Cash flows from investing activities:
Capital investments			(31.6)	(29.7)
Investments in acquired businesses			0	0
Other investing items, net			4.8	5.3
Net cash flows from investing activities			(26.8)	(24.4)
Cash flows from financing activities:
Net borrowings under credit facility			185.0	192.0
Proceeds from issuance of long-term debt			31.9	373.3
Redemption of long-term debt			(27.2)	(73.9)
Debt issuance costs			(3.1)	(8.6)
Purchase of treasury stock			0	0
Common stock dividends paid				0
Inter-company activity			(9.9)	(19.2)
SunCoke Middletown advances from (distributions to) noncontrolling interest owners			0	0
Other financing items, net			0	(0.2)
Net cash flows from financing activities			176.7	463.4
Net increase (decrease) in cash and cash equivalents			(175.5)	7.4
Cash and cash equivalents, beginning of period			203.6	19.9
Cash and cash equivalents, end of period	28.1	27.3	28.1	27.3
Other Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	200.3	224.8	626.6	705.4
Cost of products sold (exclusive of items shown separately below)	158.4	182.8	503.0	578.5
Selling and administrative expenses (exclusive of items shown separately below)	9.4	9.4	27.9	26.8
Depreciation	5.3	4.9	15.1	14.3
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	173.1	197.1	546.0	619.6
Operating profit (loss)	27.2	27.7	80.6	85.8
Interest expense	0.4	0.2	1.0	0.6
Other income (expense)	(0.9)	7.8	4.1	9.3
Income (loss) before income taxes	25.9	35.3	83.7	94.5
Income tax provision (benefit)	3.6	13.6	14.3	36.6
Equity in net income (loss) of subsidiaries	0	0	0	0
Net income (loss)	22.3	21.7	69.4	57.9
Less: Net income attributable to noncontrolling interests	16.0	8.4	47.6	19.9
Net income (loss) attributable to AK Steel Holding Corporation	6.3	13.3	21.8	38.0
Other comprehensive income (loss)	1.2	0.7	0.5	0.3
Comprehensive income (loss) attributable to AK Steel Holding Corporation	7.5	14.0	22.3	38.3
Current assets:
Cash and cash equivalents	37.6	19.8	37.6	19.8
Accounts receivable, net	66.9		66.9		54.3
Inventory, net	97.8		97.8		114.4
Deferred tax assets, current	0.2		0.2		0.2
Other current assets	3.3		3.3		1.6
Total current assets	205.8		205.8		193.9
Property, plant and equipment	605.8		605.8		588.8
Accumulated depreciation	(104.7)		(104.7)		(89.7)
Property, plant and equipment, net	501.1		501.1		499.1
Other non-current assets:
Investment in AFSG Holdings, Inc.	55.6		55.6		55.6
Investment in Magnetation LLC	190.4		190.4		150.0
Investment in affiliates	0		0		0
Inter-company accounts	831.7		831.7		843.8
Goodwill	37.1		37.1		37.1
Deferred tax assets, non-current	0.3		0.3		0.3
Other non-current assets	29.8		29.8		37.4
TOTAL ASSETS	1,851.8		1,851.8		1,817.2
Current liabilities:
Short-term borrowings under credit facility	0		0
Accounts payable	50.2		50.2		44.4
Accrued liabilities	10.1		10.1		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	60.8		60.8		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	0.6		0.6		0.5
TOTAL LIABILITIES	65.7		65.7		59.7
Total stockholders' equity (deficit)	1,365.3		1,365.3		1,343.2
Noncontrolling interests	420.8		420.8		414.3
TOTAL EQUITY (DEFICIT)	1,786.1		1,786.1		1,757.5
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,851.8		1,851.8		1,817.2
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			110.4	50.7
Cash flows from investing activities:
Capital investments			(16.5)	(19.6)
Investments in acquired businesses			(50.0)	(38.1)
Other investing items, net			10.3	(0.7)
Net cash flows from investing activities			(56.2)	(58.4)
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			0.5	(0.5)
SunCoke Middletown advances from (distributions to) noncontrolling interest owners			(41.1)	5.5
Other financing items, net			0.6	0.4
Net cash flows from financing activities			(40.0)	5.4
Net increase (decrease) in cash and cash equivalents			14.2	(2.3)
Cash and cash equivalents, beginning of period			23.4	22.1
Cash and cash equivalents, end of period	37.6	19.8	37.6	19.8
Eliminations [Member]
Condensed Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net sales	(153.1)	(170.5)	(438.3)	(513.8)
Cost of products sold (exclusive of items shown separately below)	(142.4)	(163.7)	(407.9)	(487.8)
Selling and administrative expenses (exclusive of items shown separately below)	(9.7)	(10.9)	(30.3)	(33.6)
Depreciation	0	0	0	0
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	(152.1)	(174.6)	(438.2)	(521.4)
Operating profit (loss)	(1.0)	4.1	(0.1)	7.6
Interest expense	0	0	0	0
Other income (expense)	0	0	0	0
Income (loss) before income taxes	(1.0)	4.1	(0.1)	7.6
Income tax provision (benefit)	(0.5)	1.7	(0.1)	3.1
Equity in net income (loss) of subsidiaries	24.9	44.3	56.7	750.8
Net income (loss)	24.4	46.7	56.7	755.3
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	24.4	46.7	56.7	755.3
Other comprehensive income (loss)	2.2	7.5	51.5	24.6
Comprehensive income (loss) attributable to AK Steel Holding Corporation	26.6	54.2	108.2	779.9
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	(58.6)		(58.6)		(64.8)
Inventory, net	(9.5)		(9.5)		(9.4)
Deferred tax assets, current	0		0		0
Other current assets	0		0		0
Total current assets	(68.1)		(68.1)		(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	1,455.5		1,455.5		1,323.3
Inter-company accounts	61.5		61.5		67.5
Goodwill	0		0		0
Deferred tax assets, non-current	0		0		0
Other non-current assets	0		0		0
TOTAL ASSETS	1,448.9		1,448.9		1,316.6
Current liabilities:
Short-term borrowings under credit facility	0		0
Accounts payable	(0.7)		(0.7)		(0.9)
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	(0.7)		(0.7)		(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	(0.7)		(0.7)		(0.9)
Total stockholders' equity (deficit)	1,449.6		1,449.6		1,317.5
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	1,449.6		1,449.6		1,317.5
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,448.9		1,448.9		1,316.6
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(5.9)	(4.1)
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	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			5.9	4.1
SunCoke Middletown advances from (distributions to) noncontrolling interest owners			0	0
Other financing items, net			0	0
Net cash flows from financing activities			5.9	4.1
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