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Annual report pursuant to Section 13 and 15(d)

STOCK COMPENSATION PLANS (Narrative) (Details)

v3.3.1.900
STOCK COMPENSATION PLANS (Narrative) (Details)
 3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2014
USD ($)
shares
Sep. 30, 2014
USD ($)
Sep. 30, 2015
Dec. 31, 2015
USD ($)
Agreement
Plan
shares
Dec. 31, 2014
USD ($)
$ / shares
shares
Dec. 31, 2013
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award, Number of Plans | Plan Ìý Ìý Ìý 2 Ìý Ìý
Allocated Share-based Compensation Expense | $ Ìý Ìý Ìý $ 13,900,000 $ 21,500,000 $ 19,100,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense | $ Ìý Ìý Ìý $ 0 $ 7,500,000 $ 6,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Plan Year Agreements | Agreement Ìý Ìý Ìý 3 Ìý Ìý
Number of performance shares granted Ìý Ìý Ìý 3,769,700 Ìý Ìý
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $ Ìý Ìý Ìý $ 23,500,000 Ìý Ìý
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Ìý Ìý Ìý 2 years 6 months 20 days Ìý Ìý
Option Indexed to Issuer's Equity, Strike Price | $ / shares Ìý Ìý Ìý Ìý $ 13.83 Ìý
Common Stock, Shares Authorized 400,000,000 Ìý Ìý 400,000,000 400,000,000 Ìý
2015 Equity Plan [Member] | Maximum [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Maximum number of shares that may be issued (in shares) Ìý Ìý Ìý 12,900,000 Ìý Ìý
Two Thousand Twelve Equity Plan and Amended Equity Plan [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Performance/vesting period Ìý Ìý 3 years Ìý Ìý Ìý
Payout rate, as a percentage of the original grant Ìý Ìý Ìý Ìý Ìý 23.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Available for Issuance Proposed to be added to the Plan Ìý Ìý Ìý 5,000,000 Ìý Ìý
Directors Plan [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Stock Issued During Period Value Director Stock Award | $ $ 42,500 $ 42,500 Ìý Ìý $ 85,000 Ìý
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued | $ Ìý Ìý Ìý $ 85,000 250,000 Ìý
Directors Plan [Member] | Maximum [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Maximum number of shares that may be issued (in shares) Ìý Ìý Ìý 300,000 Ìý Ìý
2012 Equity Plan [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Number of shares granted under the award Ìý Ìý Ìý 900,000 Ìý Ìý
Number of performance shares granted Ìý Ìý Ìý 900,000 Ìý Ìý
Number of restricted shares granted Ìý Ìý Ìý 400,000 Ìý Ìý
Change in Control [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Allocated Share-based Compensation Expense | $ Ìý Ìý Ìý Ìý $ 11,700,000 Ìý
2015 to 2017 Performance Period [Member] | Two Thousand Twelve Equity Plan and Amended Equity Plan [Member] | Minimum [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Payout rate, as a percentage of the original grant Ìý Ìý 0.00% Ìý Ìý Ìý
2015 to 2017 Performance Period [Member] | Two Thousand Twelve Equity Plan and Amended Equity Plan [Member] | Maximum [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Payout rate, as a percentage of the original grant Ìý Ìý 200.00% Ìý Ìý Ìý
Restricted Stock Units (RSUs) [Member] | 2015 Equity Plan [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Number of restricted shares granted Ìý Ìý Ìý 1,500,000 Ìý Ìý
Cliffs Natural Resource Inc. 2015 Employee Stock Purchase Plan [Member] Ìý Ìý Ìý Ìý Ìý Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý
Common Stock, Shares Authorized Ìý Ìý Ìý 10,000,000 Ìý Ìý