XML 75 R54.htm IDEA: XBRL DOCUMENT
v3.21.2

ACQUISITIONS - AK Steel Intangible Assets and Liabilities (Details) - AK Steel $ in Millions | 9 Months Ended
--- | ---
Sep. 30, 2021 USD ($)
Acquired Finite-Lived Intangible Assets [Line Items] |
Total identifiable intangible assets | $ 148
Weighted Average Life (In Years) | 17 years
Above-market supply contracts | $ (71)
Above-market supply contract, Weighted Average Useful Life (in years) | 12 years
Customer relationships |
Acquired Finite-Lived Intangible Assets [Line Items] |
Total identifiable intangible assets | $ 77
Weighted Average Life (In Years) | 18 years
Developed technology |
Acquired Finite-Lived Intangible Assets [Line Items] |
Total identifiable intangible assets | $ 60
Weighted Average Life (In Years) | 17 years
Trade names and trademarks |
Acquired Finite-Lived Intangible Assets [Line Items] |
Total identifiable intangible assets | $ 11
Weighted Average Life (In Years) | 10 years

X
- Definition Weighted average amortization period of finite-lived intangible liabilities assumed either individually or as part of a group of liabilities, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | clf_AssumedFinitelivedIntangibleLiabilitiesWeightedAverageUsefulLife
Namespace Prefix: | clf_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of increase in liabilities, excluding financial liabilities, lacking physical substance with a definite life, from an acquisition. + References No definition available. + Details
Name: | clf_FinitelivedIntangibleLiabilityAssumed
Namespace Prefix: | clf_
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_AcquiredFiniteLivedIntangibleAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275 + Details
Name: | us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275 + Details
Name: | us-gaap_FinitelivedIntangibleAssetsAcquired1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=clf_AKSteelMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CustomerRelationshipsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TechnologyBasedIntangibleAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TrademarksAndTradeNamesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |