Segment Information - Other Footnote (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating income (loss)
Corporate SG & A									$ (327,626)	$ (316,214)	$ (272,777)
Profit sharing									(23,064)	(42,126)	(27,764)
Operating income (loss)	$ (381,143)	$ 131,029	$ 77,559	$ 99,771	$ (81,160)	$ 188,643	$ 131,905	$ 80,932	(72,784)	320,320	386,525
Impairment charges									(428,500)	(260,000)	(308)
Assets
Cash and equivalents	727,032				361,363				727,032	361,363	395,156	$ 375,917
Accounts receivable	613,605				902,825				613,605	902,825
Inventories	1,149,390				1,618,419				1,149,390	1,618,419
Property, plant and equipment, net	2,951,210				3,123,906				2,951,210	3,123,906
Other	36,501				55,164				36,501	55,164
Total assets	6,202,082				7,233,159				6,202,082	7,233,159	5,888,534
Liabilities
Accounts payable	283,355				511,056				283,355	511,056
Income taxes payable	2,023				6,086				2,023	6,086
Accrued interest	38,502				50,405				38,502	50,405
Long-term debt	2,594,656				2,981,849				2,594,656	2,981,849
Deferred income taxes	400,770				506,482				400,770	506,482
Liabilities	3,530,631				4,311,292				3,530,631	4,311,292	3,276,165
Minnesota Ironmaking Operations
Operating income (loss)
Operating income (loss)					(260,000)
Other | Minnesota Ironmaking Operations
Operating income (loss)
Impairment charges					(260,000)
Severstal Columbus LLC
Acquisitions
Acquisition and related costs						$ 25,200				25,200
Operating Segment | Other
Operating income (loss)
Corporate SG & A									(34,700)	(42,000)	(36,000)
Company-wide equity- based compensation									(27,400)	(22,800)	(15,200)
Profit sharing									(17,700)	(36,800)	(23,400)
Other, net									(13,300)	(14,100)	(10,000)
Operating income (loss)									(148,784)	(445,549)	(177,939)
Assets
Cash and equivalents	641,900				272,300				641,900	272,300	328,300
Accounts receivable	18,800				36,800				18,800	36,800	24,700
Inventories	35,100				95,200				35,100	95,200	91,200
Property, plant and equipment, net	306,000				313,600				306,000	313,600	579,900
Intra-company debt	6,200				7,100				6,200	7,100	8,000
Other	42,500				68,400				42,500	68,400	74,800
Total assets	1,050,506				793,389				1,050,506	793,389	1,106,856
Liabilities
Accounts payable	102,300				126,900				102,300	126,900	82,800
Income taxes payable	2,200				6,100				2,200	6,100	4,000
Accrued interest	38,300				50,200				38,300	50,200	31,200
Accrued profit sharing	17,700				36,800				17,700	36,800	23,400
Long-term debt	2,588,700				2,975,000				2,588,700	2,975,000	2,074,800
Deferred income taxes	(109,000)								(109,000)
Deferred income taxes					36,900					36,900	139,100
Other	27,000				39,000				27,000	39,000	38,800
Liabilities	2,667,189				3,270,878				2,667,189	3,270,878	2,394,072
Operating Segment | Other | MINNESOTA | Minnesota Ironmaking Operations
Operating income (loss)
Operating income (loss)									(55,700)	(69,800)	(93,300)
Impairment charges										(260,000)
Operating Segment | Metals Recycling Operations
Operating income (loss)
Operating income (loss)									(448,137)	26,014	41,949
Impairment charges	(428,500)								(428,500)
Assets
Total assets	1,067,672				1,767,820				1,067,672	1,767,820	1,840,490
Liabilities
Liabilities	$ 250,719				$ 352,271				$ 250,719	$ 352,271	$ 364,231