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SHAREHOLDERS' EQUITY Schedule of Shareholders' Equity (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | Dec. 31, 2016 | Dec. 31, 2015
Stockholders' Equity Attributable to Parent | $ (833.3) |  | $ (833.3) |  | $ (1,464.3) |
Stockholders' Equity Attributable to Noncontrolling Interest | 0.2 |  | 0.2 |  | 133.8 |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest | (833.1) | $ (1,400.5) | (833.1) | $ (1,400.5) | (1,330.5) | $ (1,811.6)
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS | 53.4 | (25.8) | 57.1 | 95.0 |  |
Net Income (Loss) Attributable to Noncontrolling Interest | (0.5) | (2.0) | (3.9) | 23.5 |  |
Net Income (Loss) | 52.9 | (27.8) | 53.2 | 118.5 |  |
Other comprehensive income (loss) | 55.7 | (18.0) | 61.3 | 111.8 |  |
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest | 5.7 | 0.9 | 1.1 | 2.2 |  |
Other Comprehensive Income (Loss), Net of Tax | 8.0 | 8.7 | 5.3 | 19.0 |  |
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest |  |  | 58.5 | 137.5 |  |
Stock and Other Incentive Plans |  |  | 13.5 | 10.1 |  |
Distributions to partnership equity |  |  |  | (48.8) |  |
Distributions to noncontrolling interest |  |  | 1.8 | (2.9) |  |
Cliffs Shareholders Equity [Member] |  |  |  |  |  |
Stockholders' Equity Attributable to Parent | (833.3) | (1,544.3) | (833.3) | (1,544.3) | (1,464.3) | (1,981.4)
Net Income (Loss) Available to Common Stockholders, Basic |  |  | 57.1 | 95.0 |  |
Other comprehensive income (loss) |  |  | 4.2 | 16.8 |  |
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS |  |  | 61.3 | 111.8 |  |
Stock and Other Incentive Plans |  |  | 13.5 | 10.1 |  |
Distributions to partnership equity |  |  |  | 0.0 |  |
Distributions to noncontrolling interest |  |  | 0.0 | 0.0 |  |
Noncontrolling Interest [Member] |  |  |  |  |  |
Stockholders' Equity Attributable to Noncontrolling Interest | 0.2 | $ 143.8 | 0.2 | 143.8 | $ 133.8 | $ 169.8
Net Income (Loss) Attributable to Noncontrolling Interest |  |  | (3.9) | 23.5 |  |
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest |  |  | 1.1 | 2.2 |  |
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST |  |  | (2.8) | 25.7 |  |
Stock and Other Incentive Plans |  |  | 0.0 | 0.0 |  |
Distributions to partnership equity |  |  |  | (48.8) |  |
Distributions to noncontrolling interest |  |  | 1.8 | (2.9) |  |
Common Stock [Member] |  |  |  |  |  |
Stock Issued During Period, Value, New Issues |  |  | 661.3 | 315.2 |  |
Common Stock [Member] | Cliffs Shareholders Equity [Member] |  |  |  |  |  |
Stock Issued During Period, Value, New Issues |  |  | 661.3 | 315.2 |  |
Common Stock [Member] | Noncontrolling Interest [Member] |  |  |  |  |  |
Stock Issued During Period, Value, New Issues |  |  | 0.0 | $ 0.0 |  |
Tilden [Member] |  |  |  |  |  |
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests | 15.9 |  | (105.0) |  |  |
Tilden [Member] | Cliffs Shareholders Equity [Member] |  |  |  |  |  |
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests |  |  | (89.1) |  |  |
Tilden [Member] | Noncontrolling Interest [Member] |  |  |  |  |  |
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests |  |  | (15.9) |  |  |
Empire [Member] |  |  |  |  |  |
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests | $ 116.7 |  | (132.7) |  |  |
Empire [Member] | Cliffs Shareholders Equity [Member] |  |  |  |  |  |
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests |  |  | (16.0) |  |  |
Empire [Member] | Noncontrolling Interest [Member] |  |  |  |  |  |
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests |  |  | $ (116.7) |  |  |

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