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Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details)

v2.4.0.6
FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 12 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Mar. 31, 2013
Empire [Member]
Dec. 31, 2012
Empire [Member]
Dec. 31, 2002
Empire [Member]
Dec. 31, 2002
Prior [Member]
Empire [Member]
Dec. 31, 2002
Current [Member]
Empire [Member]
Mar. 31, 2013
Other Current Assets [Member]
Empire [Member]
Dec. 31, 2012
Other Current Assets [Member]
Empire [Member]
Mar. 31, 2013
U.S. Iron Ore [Member]
Dec. 31, 2012
U.S. Iron Ore [Member]
Dec. 31, 2012
Amapa [Member]
Dec. 31, 2012
Equity Method Investments [Member]
Amapa [Member]
Mar. 31, 2013
Equity Method Investments [Member]
Amapa [Member]
Fair Value, Assets And Liabilities Components [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Transfer of derivative assets from level 3 to level 2 $ 0 $ 0 Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Transfer of derivative assets from level 2 to level 3 0 0 Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Management Estimate of 62% Fe 62.00% Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Maximum deferred portion of supplemental payments Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 22.3 Ìý Ìý Ìý Ìý
Supply agreement, customer receivable, stated interest rate 9.00% Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Supply agreement, customer receivable, description of variable rate basis prime rate Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Other current assets 297.9 Ìý 321.6 Ìý Ìý Ìý Ìý Ìý Ìý Ìý 16.7 22.3 Ìý Ìý Ìý
Supply agreement, customer receivable, basis spread on variable rate 3.50% Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Fair value of the receivable Ìý Ìý Ìý 19.1 21.3 Ìý Ìý Ìý Ìý Ìý 16.1 21.3 Ìý Ìý Ìý
Estimated credit-adjusted risk-free interest rate Ìý Ìý Ìý 2.24% 2.85% Ìý Ìý Ìý Ìý Ìý 2.14% 2.81% Ìý Ìý Ìý
Interest Percentage Ìý Ìý Ìý Ìý Ìý Ìý 46.70% Ìý Ìý Ìý Ìý Ìý Ìý Ìý 30.00%
Equity Method Investments, Fair Value Disclosure Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 72.5 Ìý Ìý
Percent ownership interest after transaction Ìý Ìý Ìý Ìý Ìý Ìý Ìý 79.00% Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Long term accounts notes and loans receivable net noncurrent Ìý Ìý Ìý 17.4 19.3 120.0 Ìý Ìý 10.0 10.0 Ìý Ìý Ìý Ìý Ìý
Impairment of equity method investment Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý $ 365.4 Ìý