Supplemental Guarantor Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010
Condensed Statements of Operations [Abstract]
Net sales	$ 1,463.5	$ 1,585.8	$ 4,510.6	$ 4,958.8
Cost of products sold (exclusive of items shown below)	1,385.0	1,482.6	4,186.4	4,585.2
Selling and administrative expenses (exclusive of items shown below)	51.9	54.6	158.5	161.6
Depreciation	48.2	46.1	144.9	139.3
Pension and OPEB expense (income)	(9.6)	(8.9)	(28.0)	(26.7)
Total operating costs	1,475.5	1,574.4	4,461.8	4,859.4
Operating profit (loss)	(12.0)	11.4	48.8	99.4
Interest expense	22.4	13.5	60.4	33.7
Other income (expense)	5.7	(4.7)	1.9	(1.3)
Income (loss) before income taxes	(28.7)	(6.8)	(9.7)	64.4
Income tax provision (benefit)	23.8	(0.7)	767.3	29.6
Equity in net income (loss) of subsidiaries	0	0	0	0
Net income (loss)	(52.5)	(6.1)	(777.0)	34.8
Less: Net income (loss) attributable to noncontrolling interests	8.4	(2.6)	19.9	(3.5)
Net income (loss) attributable to AK Steel Holding Corporation	(60.9)	(3.5)	(796.9)	38.3
Comprehensive income (loss)	(60.7)	(21.0)	(801.9)	(13.3)
Current assets:
Cash and cash equivalents	47.1	58.7	47.1	58.7
Accounts receivable, net	565.6		565.6		564.2
Inventory, net	727.8		727.8		418.7
Deferred tax assets, current	32.7		32.7		216.5
Other current assets	33.7		33.7		33.0
Total current assets	1,406.9		1,406.9		1,274.4
Property, plant and equipment	5,984.5		5,984.5		5,967.2
Accumulated depreciation	(3,942.5)		(3,942.5)		(3,797.0)
Property, plant and equipment, net	2,042.0		2,042.0		2,170.2
Other non-current assets:
Investment in AFSG Holdings, Inc.	55.6		55.6		55.6
Investment in Magnetation LLC	129.6		129.6		101.2
Investment in affiliates	0		0		0
Inter-company accounts	0		0		0
Goodwill	37.1		37.1		37.1
Deferred tax assets, non-current	146.6		146.6		716.5
Other non-current assets	102.9		102.9		94.9
TOTAL ASSETS	3,920.7		3,920.7		4,449.9
Current liabilities:
Short-term borrowings under credit facility	42.0		42.0		250.0
Accounts payable	603.2		603.2		583.6
Accrued liabilities	185.6		185.6		172.8
Current portion of long-term debt	0.7		0.7		0.7
Current portion of pension and other postretirement benefit obligations	125.4		125.4		130.0
Total current liabilities	956.9		956.9		1,137.1
Non-current liabilities:
Long-term debt, including $400.0 of credit facility borrowings at September 30, 2012	1,349.5		1,349.5		650.0
Pension and other postretirement benefit obligations	1,503.4		1,503.4		1,744.8
Other non-current liabilities	524.8		524.8		540.8
Total non-current liabilities	3,377.7		3,377.7		2,935.6
TOTAL LIABILITIES	4,334.6		4,334.6		4,072.7
TOTAL STOCKHOLDERS' EQUITY (DEFICIT)	(434.5)		(434.5)		388.5
Noncontrolling interests	20.6		20.6		(11.3)
TOTAL EQUITY (DEFICIT)	(413.9)	619.4	(413.9)	619.4	377.2	641.1
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,920.7		3,920.7		4,449.9
Condensed Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(387.9)	(355.4)
Cash flows from investing activities:
Capital investments			(49.3)	(251.2)
Investments in acquired businesses			(38.1)	0
Other investing items, net			4.6	0.7
Net cash flows from investing activities			(82.8)	(250.5)
Cash flows from financing activities:
Net borrowings under credit facility			192.0	295.0
Proceeds from issuance of long-term debt			373.3	0
Redemption of long-term debt			(73.9)	(0.5)
Debt issuance costs			(8.6)	(9.2)
Proceeds from exercise of stock options			0	0.2
Purchase of treasury stock			(1.7)	(1.4)
Common stock dividends paid			(11.0)	(16.5)
Inter-company activity			0	0
SunCoke Middletown advances from noncontrolling interest owner			5.5	180.3
Other financing items, net			0.2	(0.1)
Net cash flows from financing activities			475.8	447.8
Net increase (decrease) in cash and cash equivalents			5.1	(158.1)
Cash and cash equivalents, beginning of period			42.0	216.8
Cash and cash equivalents, end of period	47.1	58.7	47.1	58.7
AK Holding [Member]
Condensed Statements of Operations [Abstract]
Net sales	0	0	0	0
Cost of products sold (exclusive of items shown below)	0	0	0	0
Selling and administrative expenses (exclusive of items shown below)	0.9	1.0	3.6	3.6
Depreciation	0	0	0	0
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	0.9	1.0	3.6	3.6
Operating profit (loss)	(0.9)	(1.0)	(3.6)	(3.6)
Interest expense	0	0	0	0
Other income (expense)	0	0	0	0
Income (loss) before income taxes	(0.9)	(1.0)	(3.6)	(3.6)
Income tax provision (benefit)	0	(0.5)	0	(1.4)
Equity in net income (loss) of subsidiaries	(60.0)	(3.0)	(793.3)	40.5
Net income (loss)	(60.9)	(3.5)	(796.9)	38.3
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(60.9)	(3.5)	(796.9)	38.3
Comprehensive income (loss)	(69.1)	(18.4)	(821.8)	(9.8)
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	(2,454.5)		(2,454.5)		(1,589.1)
Inter-company accounts	2,019.8		2,019.8		1,977.4
Goodwill	0		0		0
Deferred tax assets, non-current	0		0		0
Other non-current assets	0		0		0
TOTAL ASSETS	(434.5)		(434.5)		388.5
Current liabilities:
Short-term borrowings under credit facility	0		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, including $400.0 of credit facility borrowings at September 30, 2012	0		0		0
Pension and other postretirement benefit obligations	0		0		0
Other non-current liabilities	0		0		0
Total non-current liabilities	0		0		0
TOTAL LIABILITIES	0		0		0
TOTAL STOCKHOLDERS' EQUITY (DEFICIT)	(434.5)		(434.5)		388.5
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	(434.5)		(434.5)		388.5
TOTAL LIABILITIES AND EQUITY (DEFICIT)	(434.5)		(434.5)		388.5
Condensed Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(2.9)	(1.5)
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
Redemption of long-term debt			0	0
Debt issuance costs			0	0
Proceeds from exercise of stock options				0.2
Purchase of treasury stock			(1.7)	(1.4)
Common stock dividends paid			(11.0)	(16.5)
Inter-company activity			15.6	19.2
SunCoke Middletown advances from noncontrolling interest owner			0	0
Other financing items, net			0	0
Net cash flows from financing activities			2.9	1.5
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 Statements of Operations [Abstract]
Net sales	1,409.2	1,529.1	4,319.0	4,756.0
Cost of products sold (exclusive of items shown below)	1,365.9	1,443.6	4,095.7	4,441.5
Selling and administrative expenses (exclusive of items shown below)	52.5	54.1	161.7	168.3
Depreciation	43.3	44.5	130.6	134.6
Pension and OPEB expense (income)	(9.6)	(8.9)	(28.0)	(26.7)
Total operating costs	1,452.1	1,533.3	4,360.0	4,717.7
Operating profit (loss)	(42.9)	(4.2)	(41.0)	38.3
Interest expense	22.2	13.5	59.8	33.7
Other income (expense)	(2.1)	(2.3)	(7.4)	(5.7)
Income (loss) before income taxes	(67.2)	(20.0)	(108.2)	(1.1)
Income tax provision (benefit)	8.5	(6.9)	727.6	3.5
Equity in net income (loss) of subsidiaries	15.7	10.1	42.5	45.1
Net income (loss)	(60.0)	(3.0)	(793.3)	40.5
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	(60.0)	(3.0)	(793.3)	40.5
Comprehensive income (loss)	(68.2)	(17.9)	(818.2)	(7.6)
Current assets:
Cash and cash equivalents	27.3	35.3	27.3	35.3
Accounts receivable, net	579.8		579.8		587.5
Inventory, net	611.5		611.5		304.6
Deferred tax assets, current	32.4		32.4		216.3
Other current assets	30.2		30.2		31.9
Total current assets	1,281.2		1,281.2		1,160.2
Property, plant and equipment	5,402.2		5,402.2		5,377.2
Accumulated depreciation	(3,857.5)		(3,857.5)		(3,726.9)
Property, plant and equipment, net	1,544.7		1,544.7		1,650.3
Other non-current assets:
Investment in AFSG Holdings, Inc.	0		0		0
Investment in Magnetation LLC	0		0		0
Investment in affiliates	2,454.5		2,454.5		1,589.1
Inter-company accounts	(4,069.0)		(4,069.0)		(3,207.3)
Goodwill	0		0		0
Deferred tax assets, non-current	146.4		146.4		716.3
Other non-current assets	65.7		65.7		64.4
TOTAL ASSETS	1,423.5		1,423.5		1,973.0
Current liabilities:
Short-term borrowings under credit facility	42.0		42.0		250.0
Accounts payable	583.7		583.7		525.4
Accrued liabilities	175.0		175.0		162.3
Current portion of long-term debt	0.7		0.7		0.7
Current portion of pension and other postretirement benefit obligations	125.0		125.0		129.6
Total current liabilities	926.4		926.4		1,068.0
Non-current liabilities:
Long-term debt, including $400.0 of credit facility borrowings at September 30, 2012	1,349.5		1,349.5		650.0
Pension and other postretirement benefit obligations	1,499.5		1,499.5		1,740.7
Other non-current liabilities	102.6		102.6		103.4
Total non-current liabilities	2,951.6		2,951.6		2,494.1
TOTAL LIABILITIES	3,878.0		3,878.0		3,562.1
TOTAL STOCKHOLDERS' EQUITY (DEFICIT)	(2,454.5)		(2,454.5)		(1,589.1)
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	(2,454.5)		(2,454.5)		(1,589.1)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,423.5		1,423.5		1,973.0
Condensed Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(431.6)	(366.7)
Cash flows from investing activities:
Capital investments			(29.7)	(87.8)
Investments in acquired businesses			0
Other investing items, net			5.3	1.5
Net cash flows from investing activities			(24.4)	(86.3)
Cash flows from financing activities:
Net borrowings under credit facility			192.0	295.0
Proceeds from issuance of long-term debt			373.3
Redemption of long-term debt			(73.9)	(0.5)
Debt issuance costs			(8.6)	(9.2)
Proceeds from exercise of stock options				0
Purchase of treasury stock			0	0
Common stock dividends paid			0	0
Inter-company activity			(19.2)	1.7
SunCoke Middletown advances from noncontrolling interest owner			0	0
Other financing items, net			(0.2)	(0.1)
Net cash flows from financing activities			463.4	286.9
Net increase (decrease) in cash and cash equivalents			7.4	(166.1)
Cash and cash equivalents, beginning of period			19.9	201.4
Cash and cash equivalents, end of period	27.3	35.3	27.3	35.3
Other [Member]
Condensed Statements of Operations [Abstract]
Net sales	224.8	193.0	705.4	569.0
Cost of products sold (exclusive of items shown below)	182.8	161.3	578.5	475.9
Selling and administrative expenses (exclusive of items shown below)	9.4	11.2	26.8	26.6
Depreciation	4.9	1.6	14.3	4.7
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	197.1	174.1	619.6	507.2
Operating profit (loss)	27.7	18.9	85.8	61.8
Interest expense	0.2	0	0.6	0
Other income (expense)	7.8	(1.4)	9.3	6.4
Income (loss) before income taxes	35.3	17.5	94.5	68.2
Income tax provision (benefit)	13.6	7.9	36.6	27.2
Equity in net income (loss) of subsidiaries	0	0	0	0
Net income (loss)	21.7	9.6	57.9	41.0
Less: Net income (loss) attributable to noncontrolling interests	8.4	(2.6)	19.9	(3.5)
Net income (loss) attributable to AK Steel Holding Corporation	13.3	12.2	38.0	44.5
Comprehensive income (loss)	22.4	8.1	58.2	41.0
Current assets:
Cash and cash equivalents	19.8	23.4	19.8	23.4
Accounts receivable, net	91.9		91.9		69.8
Inventory, net	125.4		125.4		122.1
Deferred tax assets, current	0.3		0.3		0.2
Other current assets	3.3		3.3		0.9
Total current assets	240.7		240.7		215.1
Property, plant and equipment	582.3		582.3		590.0
Accumulated depreciation	(85.0)		(85.0)		(70.1)
Property, plant and equipment, net	497.3		497.3		519.9
Other non-current assets:
Investment in AFSG Holdings, Inc.	55.6		55.6		55.6
Investment in Magnetation LLC	129.6		129.6		101.2
Investment in affiliates	1,243.2		1,243.2		1,204.3
Inter-company accounts	(416.5)		(416.5)		(401.7)
Goodwill	37.1		37.1		37.1
Deferred tax assets, non-current	0.2		0.2		0.2
Other non-current assets	37.2		37.2		30.5
TOTAL ASSETS	1,824.4		1,824.4		1,762.2
Current liabilities:
Short-term borrowings under credit facility	0		0		0
Accounts payable	43.4		43.4		59.4
Accrued liabilities	10.6		10.6		10.5
Current portion of long-term debt	0		0		0
Current portion of pension and other postretirement benefit obligations	0.4		0.4		0.4
Total current liabilities	54.4		54.4		70.3
Non-current liabilities:
Long-term debt, including $400.0 of credit facility borrowings at September 30, 2012	0		0		0
Pension and other postretirement benefit obligations	3.9		3.9		4.1
Other non-current liabilities	422.2		422.2		437.4
Total non-current liabilities	426.1		426.1		441.5
TOTAL LIABILITIES	480.5		480.5		511.8
TOTAL STOCKHOLDERS' EQUITY (DEFICIT)	1,323.3		1,323.3		1,261.7
Noncontrolling interests	20.6		20.6		(11.3)
TOTAL EQUITY (DEFICIT)	1,343.9		1,343.9		1,250.4
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,824.4		1,824.4		1,762.2
Condensed Statements of Cash Flows [Abstract]
Net cash flows from operating activities			50.7	11.1
Cash flows from investing activities:
Capital investments			(19.6)	(163.4)
Investments in acquired businesses			(38.1)
Other investing items, net			(0.7)	(0.8)
Net cash flows from investing activities			(58.4)	(164.2)
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
Proceeds from exercise of stock options				0
Purchase of treasury stock			0	0
Common stock dividends paid			0	0
Inter-company activity			(0.5)	(19.2)
SunCoke Middletown advances from noncontrolling interest owner			5.5	180.3
Other financing items, net			0.4	0
Net cash flows from financing activities			5.4	161.1
Net increase (decrease) in cash and cash equivalents			(2.3)	8.0
Cash and cash equivalents, beginning of period			22.1	15.4
Cash and cash equivalents, end of period	19.8	23.4	19.8	23.4
Eliminations [Member]
Condensed Statements of Operations [Abstract]
Net sales	(170.5)	(136.3)	(513.8)	(366.2)
Cost of products sold (exclusive of items shown below)	(163.7)	(122.3)	(487.8)	(332.2)
Selling and administrative expenses (exclusive of items shown below)	(10.9)	(11.7)	(33.6)	(36.9)
Depreciation	0	0	0	0
Pension and OPEB expense (income)	0	0	0	0
Total operating costs	(174.6)	(134.0)	(521.4)	(369.1)
Operating profit (loss)	4.1	(2.3)	7.6	2.9
Interest expense	0	0	0	0
Other income (expense)	0	(1.0)	0	(2.0)
Income (loss) before income taxes	4.1	(3.3)	7.6	0.9
Income tax provision (benefit)	1.7	(1.2)	3.1	0.3
Equity in net income (loss) of subsidiaries	44.3	(7.1)	750.8	(85.6)
Net income (loss)	46.7	(9.2)	755.3	(85.0)
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to AK Steel Holding Corporation	46.7	(9.2)	755.3	(85.0)
Comprehensive income (loss)	54.2	7.2	779.9	(36.9)
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	(106.1)		(106.1)		(93.1)
Inventory, net	(9.1)		(9.1)		(8.0)
Deferred tax assets, current	0		0		0
Other current assets	0		0		0
Total current assets	(115.2)		(115.2)		(101.1)
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	(1,243.2)		(1,243.2)		(1,204.3)
Inter-company accounts	2,465.7		2,465.7		1,631.6
Goodwill	0		0		0
Deferred tax assets, non-current	0		0		0
Other non-current assets	0		0		0
TOTAL ASSETS	1,107.3		1,107.3		326.2
Current liabilities:
Short-term borrowings under credit facility	0		0		0
Accounts payable	(23.9)		(23.9)		(1.2)
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	(23.9)		(23.9)		(1.2)
Non-current liabilities:
Long-term debt, including $400.0 of credit facility borrowings at September 30, 2012	0		0		0
Pension and other postretirement benefit obligations	0		0		0
Other non-current liabilities	0		0		0
Total non-current liabilities	0		0		0
TOTAL LIABILITIES	(23.9)		(23.9)		(1.2)
TOTAL STOCKHOLDERS' EQUITY (DEFICIT)	1,131.2		1,131.2		327.4
Noncontrolling interests	0		0		0
TOTAL EQUITY (DEFICIT)	1,131.2		1,131.2		327.4
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,107.3		1,107.3		326.2
Condensed Statements of Cash Flows [Abstract]
Net cash flows from operating activities			(4.1)	1.7
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
Redemption of long-term debt			0	0
Debt issuance costs			0	0
Proceeds from exercise of stock options				0
Purchase of treasury stock			0	0
Common stock dividends paid			0	0
Inter-company activity			4.1	(1.7)
SunCoke Middletown advances from noncontrolling interest owner			0	0
Other financing items, net			0	0
Net cash flows from financing activities			4.1	(1.7)
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