XML 94 R52.htm IDEA: XBRL DOCUMENT
v3.20.1

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Equity Method Investments) (Details) (Details) | Mar. 31, 2020
--- | ---
Combined Metals of Chicago, LLC [Member] |
Schedule of Equity Method Investments [Line Items] |
Equity Method Investment, Ownership Percentage | 40.00%
Hibbing Taconite Company [Member] |
Schedule of Equity Method Investments [Line Items] |
Equity Method Investment, Ownership Percentage | 23.00%
Spartan Steel Coating, LLC [Member] |
Schedule of Equity Method Investments [Line Items] |
Equity Method Investment, Ownership Percentage | 48.00%

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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=114001798&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_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=clf_CombinedMetalsofChicagoLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=clf_HibbingTaconiteCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=clf_SpartanSteelCoatingLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |