XML 91 R77.htm IDEA: XBRL DOCUMENT
v3.10.0.1

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Loss Contingencies [Line Items] |  |
Environmental | $ 2.7 | $ 2.9
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent | 177.3 | 171.3
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current | 2.9 | 3.6
Environmental Loss Contingency And Mine Reclamation And Closing Liability Noncurrent | 174.4 | 167.7
Owned Or Operating Facilities [Member] |  |
Loss Contingencies [Line Items] |  |
Mine Reclamation and Closing Liability, current and noncurrent | $ 174.6 | $ 168.4

X
- Definition Environmental Loss Contingency And Mine Reclamation And Closing Liability Current + References No definition available. + Details
Name: | clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrent
Namespace Prefix: | clf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent + References No definition available. + Details
Name: | clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrentAndNoncurrent
Namespace Prefix: | clf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of environmental loss contingencies, such as presence of hazardous waste, relevant information from reports issued by regulators, and estimated costs to achieve compliance with regulatory requirements. As well as, the amount of a reclamation and mine closing liability that is associated with a legal obligation for the closure and reclamation of a mine including the removal of buildings, equipment, machinery and other physical remnants of mining, closure of tailings impoundments, leach pads and other mine features, and contouring, covering and revegetation of waste rock piles and other disturbed areas. + References No definition available. + Details
Name: | clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityNoncurrent
Namespace Prefix: | clf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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 Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 + Details
Name: | us-gaap_AccrualForEnvironmentalLossContingencies
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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