XML 84 R68.htm IDEA: XBRL DOCUMENT
v3.8.0.1

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 USD ($) T | Sep. 30, 2017 USD ($)
Accrual for Environmental Loss Contingencies, Period Increase (Decrease) | $ 9.2 |
Reserve increase (decrease), tons | T | 115,000,000 |
Selenium [Domain] |  |
Accrual for Environmental Loss Contingencies, Period Increase (Decrease) | $ 29.6 |
Eastern Canadian Iron Ore [Member] | Owned Or Operating Facilities [Member] |  |
Mine Reclamation and Closing Liability, current and noncurrent | $ 206.8 | $ 216.2

X
- Definition Mine Reclamation and Closing Liability, current and noncurrent + References No definition available. + Details
Name: | clf_MineReclamationAndClosingLiabilityCurrentAndNoncurrent
Namespace Prefix: | clf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Reserve increase (decrease), tons + References No definition available. + Details
Name: | clf_Reserveincreasedecreasetons
Namespace Prefix: | clf_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | duration

X
- Definition Increase (decrease) in the accrual for environmental loss contingencies during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
Name: | us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=clf_SeleniumDomain
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=clf_EasternCanadianIronOreMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=clf_OwnedOrOperatingFacilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |