XML 98 R82.htm IDEA: XBRL DOCUMENT
v3.8.0.1

RELATED PARTIES (Summary Of Other Ownership Interests) (Details) - Hibbing [Member] | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Arcelor Mittal [Member] |  |
Related Party Transaction [Line Items] |  |
Ownership interest, equity method investment | 62.30% |
U. S. Steel Canada [Member] |  |
Related Party Transaction [Line Items] |  |
Ownership interest, equity method investment | 14.70% |
Other Noncurrent Assets [Member] |  |
Related Party Transaction [Line Items] |  |
Ownership interest, equity method investment | 23.00% | 23.00%

X
- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571 + Details
Name: | us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
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_RelatedPartyTransactionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=clf_HibbingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=clf_ArcelorMittalMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=clf_USSteelCanadaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_OtherNoncurrentAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |