Cleveland-Cliffs Inc. Annual report pursuant to Section 13 and 15(d)

SEGMENT REPORTING SEGMENTS REPORTING (Revenue by Geographical Location) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 476.0	$ 593.2	$ 498.1	$ 446.0	$ 1,030.3	$ 979.7	$ 747.7	$ 615.5	$ 2,013.3	$ 3,373.2	$ 3,890.8
PROPERTY, PLANT AND EQUIPMENT, NET	1,059.0				1,070.5				1,059.0	1,070.5	1,870.8
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									1,206.4	1,923.2	1,543.9
PROPERTY, PLANT AND EQUIPMENT, NET	1,012.7				998.1				1,012.7	998.1	1,120.6
AUSTRALIA
Revenues from External Customers and Long-Lived Assets [Line Items]
PROPERTY, PLANT AND EQUIPMENT, NET	$ 46.3				$ 72.4				46.3	72.4	750.2
China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									370.8	662.7	1,165.3
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									282.4	430.5	758.5
Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 153.7	$ 356.8	$ 423.1