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金融工具公允价值金融工具公允价值（非经常性公允价值计量）（详细信息）（美元）
除非另有说明，单位为百万
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3个月结束 |
12个月结束 |
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2015年3月31日
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2014年12月31日
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 商誉、减值损失 |
0美元us-gaap_GoodwillImpairmentLoss |
73.5美元us-gaap_GoodwillImpairmentLoss |
| 资产，公允价值披露，非经常性 |
397.2us-gaap_AssetsFairValueDisclosureNonrecurring |
79.4us-gaap_AssetsFairValueDisclosureNonrecurring |
| 商誉和其他长期资产的减值 |
269.5clf_ImpairmentCharges |
644.7clf_ImpairmentCharges |
| 公允价值，输入值，第1级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 资产，公允价值披露，非经常性 |
0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member |
0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member |
| 公允价值，输入值，第2级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 资产，公允价值披露，非经常性 |
397.2us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member |
0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member |
| 公允价值，输入值，第3级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 资产，公允价值披露，非经常性 |
0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member |
79.4us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member |
| 全球勘探投资风险[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 权益法投资，公允价值披露 |
|
0us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember |
| 权益法投资，临时减值除外 |
|
9.2us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember |
| 全球勘探风险投资[成员]|公允价值、投入、一级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 权益法投资，公允价值披露 |
|
0us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember |
| 全球勘探风险投资[成员]|公允价值、投入、第2级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 权益法投资，公允价值披露 |
|
0us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember |
| 全球勘探风险投资[成员]|公允价值，投入，第3级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 权益法投资，公允价值披露 |
|
0us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember |
| 亚太铁矿石〔成员〕 |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 商誉，公允价值披露 |
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0us-gaap_GoodwillFairValueDisclosure
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 商誉、减值损失 |
|
73.5us-gaap_GoodwillImpairmentLoss
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 亚太地区铁矿石[成员]|公允价值，投入，第一级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 商誉，公允价值披露 |
|
0us-gaap_GoodwillFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 亚太地区铁矿石[成员]|公允价值，投入，第2级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 商誉，公允价值披露 |
|
0us-gaap_GoodwillFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 亚太地区铁矿石[成员]|公允价值，投入，第3级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
|
|
| 商誉，公允价值披露 |
|
0us-gaap_GoodwillFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 其他报告单位〔成员〕 |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 财产、厂房和设备，公允价值披露 |
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0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember |
| 有形资产减值费用 |
|
11.3us-gaap_TangibleAssetImpairmentCharges
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember |
| 其他报告单位[成员]|公允价值，输入值，第1级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 财产、厂房和设备，公允价值披露 |
|
0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember |
| 其他报告单位[成员]|公允价值，输入值，第2层[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 财产、厂房和设备，公允价值披露 |
|
0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember |
| 其他报告单位[成员]|公允价值，输入值，第3级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
|
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| 财产、厂房和设备，公允价值披露 |
|
0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember |
| 亚太地区[会员]|亚太铁矿石[会员]|公允价值、投入、第2级[会员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 财产、厂房和设备，公允价值披露 |
|
0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_AssetgroupAxis
= us-gaap_AsiaPacificMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 有限寿命无形资产，公允价值披露 |
|
0us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure
/ clf_AssetgroupAxis
= us-gaap_AsiaPacificMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 亚太铁矿石[成员]|亚太铁矿石[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 财产、厂房和设备，公允价值披露 |
|
72.4us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 有形资产减值费用 |
|
526.5us-gaap_TangibleAssetImpairmentCharges
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 其他资产减值费用 |
|
24.2us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 有限寿命无形资产，公允价值披露 |
|
7.0us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 亚太地区铁矿石[成员]|00亚太地区铁矿石[成员]|公允价值，投入，第一级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 财产、厂房和设备，公允价值披露 |
|
0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 有限寿命无形资产，公允价值披露 |
|
0us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 亚太地区铁矿石[会员]|亚太地区铁矿石[会员]|公允价值、投入、三级[会员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 财产、厂房和设备，公允价值披露 |
|
72.4us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 有限寿命无形资产，公允价值披露 |
|
7.0us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember |
| 五亿四千四百万七亿七千二百二十二张留置权票[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
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| 债务工具，公允价值披露 |
397.2us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember |
|
| 新发行债券的收益 |
269.5clf_Gainonnewdebtissued
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember |
|
| 五亿四千四百万柒点柒点二十二秒留置权票据[成员]|公允价值，输入，第一级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
|
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| 债务工具，公允价值披露 |
0us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member |
|
| 五亿四千四百万柒点柒点二十二秒留置权票据[成员]|公允价值，输入，第二级[成员] |
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
|
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| 债务工具，公允价值披露 |
397.2us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member |
0us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member |
| 五亿四千四百万七亿七千二百二十二张留置权票据[成员]|公允价值，输入，第3级[成员] |
|
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| 公允价值、经常性和非经常性计量资产和负债[细目] |
|
|
| 债务工具，公允价值披露 |
0美元us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member |
|