Quarterly report pursuant to Section 13 or 15(d)

INVENTORIES (Schedule Of Inventories) (Details)

v2.4.1.9
INVENTORIES (Schedule Of Inventories) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Inventory, Net [Abstract]    
Finished Goods $ 309.6us-gaap_InventoryFinishedGoodsNetOfReserves $ 158.5us-gaap_InventoryFinishedGoodsNetOfReserves
Work-in Process 98.9us-gaap_InventoryWorkInProcessNetOfReserves 101.6us-gaap_InventoryWorkInProcessNetOfReserves
Total Inventory 408.5us-gaap_InventoryNet 260.1us-gaap_InventoryNet
U.S. Iron Ore [Member]    
Inventory, Net [Abstract]    
Finished Goods 294.5us-gaap_InventoryFinishedGoodsNetOfReserves
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
132.1us-gaap_InventoryFinishedGoodsNetOfReserves
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Work-in Process 13.9us-gaap_InventoryWorkInProcessNetOfReserves
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
13.5us-gaap_InventoryWorkInProcessNetOfReserves
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Total Inventory 308.4us-gaap_InventoryNet
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
145.6us-gaap_InventoryNet
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Asia Pacific Iron Ore [Member]    
Inventory, Net [Abstract]    
Finished Goods 15.1us-gaap_InventoryFinishedGoodsNetOfReserves
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
26.4us-gaap_InventoryFinishedGoodsNetOfReserves
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Work-in Process 85.0us-gaap_InventoryWorkInProcessNetOfReserves
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
88.1us-gaap_InventoryWorkInProcessNetOfReserves
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Total Inventory $ 100.1us-gaap_InventoryNet
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
$ 114.5us-gaap_InventoryNet
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember