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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Tables) | 12 Months Ended
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Dec. 31, 2018
Schedule Of Subsidiaries | The consolidated financial statements include our accounts and the accounts of our wholly owned subsidiaries, including the following iron ore operations at December 31, 2018:
Name |  | Location |  | Status of Operations
Northshore |  | Minnesota |  | Active
United Taconite |  | Minnesota |  | Active
Tilden |  | Michigan |  | Active
Empire |  | Michigan |  | Indefinitely Idled
Depreciation Disclosure [Table Text Block] | Depreciation and depletion is provided over the following estimated useful lives:
Asset Class |  | Basis |  | Life
Office and information technology |  | Straight line |  | 3 to 15 years
Buildings |  | Straight line |  | 45 years
Mining equipment |  | Straight line/Double declining balance |  | 3 to 20 years
Processing equipment |  | Straight line |  | 10 to 45 years
Electric power facilities |  | Straight line |  | 10 to 45 years
Land improvements |  | Straight line |  | 20 to 45 years
Asset retirement obligation |  | Straight line |  | Life of mine
Mineral rights |  | Units of production |  | Life of mine
Estimated Useful Lives Of Intangible Assets Subject To Periodic Amortization On Straight Line Basis Table [Text Block] | Our mine permits are subject to periodic amortization on a straight line basis over their estimated useful life, which corresponds with the life of mine.
Contract with Customer, Asset and Liability [Table Text Block] | The table below summarizes our deferred revenue balances:
| (In Millions)
| Deferred Revenue (Current)1 |  | Deferred Revenue (Long-Term)
| Year Ended December 31, |  | Year Ended December 31,
| 2018 |  | 2017 |  | 2018 |  | 2017
Opening balance as of January 1 | $ | 23.8 |  |  | $ | 16.2 |  |  | $ | 51.4 |  |  | $ | 64.3 |
Closing balance as of December 31 | 21.0 |  |  | 22.4 |  |  | 38.5 |  |  | 51.4 |
Increase (Decrease) | $ | (2.8 | ) |  | $ | 6.2 |  |  | $ | (12.9 | ) |  | $ | (12.9 | )
1 The opening balance for the year ended December 31, 2018 includes a $1.4 million adjustment from the December 31, 2017 balance due to the adoption of Topic 606.
Reimbursements Revenue Disclosure [Table Text Block] | The following table is a summary of reimbursements in our operations:
|  | (In Millions)
|  | Year Ended December 31,
|  | 2018 |  | 2017 |  | 2016
Reimbursements for: |  |  |  |  |  |
Freight |  | $ | 160.1 |  |  | $ | 166.7 |  |  | $ | 106.8 |
Venture partners’ cost |  | — |  |  | 54.7 |  |  | 68.0 |
Total reimbursements |  | $ | 160.1 |  |  | $ | 221.4 |  |  | $ | 174.8 |
Foreign Currency Transaction [Table Text Block] | The following represents the net gain (loss) related to impact of transaction gains and losses from continuing operations resulting from remeasurement:
|  | (In Millions)
|  | 2018 |  | 2017 |  | 2016
Remeasurement of intercompany loans |  | $ | (0.7 | ) |  | $ | 16.6 |  |  | $ | (16.6 | )
Other remeasurement |  | (0.2 | ) |  | (2.7 | ) |  | (1.2 | )
Total |  | $ | (0.9 | ) |  | $ | 13.9 |  |  | $ | (17.8 | )

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- Definition Describes the methodology and periods of time over which an entity anticipates to receive utility from its property, plant and equipment (that is, the periods of time over which an entity allocates the initial cost of its property, plant and equipment and the estimated useful life of the asset in a systematic and rational manner.) + References No definition available. + Details
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- Definition Disclosure of subsidiaries or other investments that are consolidated. + References No definition available. + Details
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- Definition Tabular disclosure of contract balances and changes in contract balances. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045 + Details
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