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

Annual report pursuant to Section 13 and 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS (Carrying Value And Fair Value Of Financial Instruments Disclosure) (Details)

FAIR VALUE OF FINANCIAL INSTRUMENTS (Carrying Value And Fair Value Of Financial Instruments Disclosure) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Interest Rate Swap [Member]
Long-term debt:
Fair Value Adjustment to Interest Rate Hedge	$ 0.2	$ 1.4
Reported Value Measurement [Member]
Long-term debt:
Long-term Debt, Fair Value	2,092.9	2,304.2
Reported Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swap [Member]
Long-term debt:
Fair Value Adjustment to Interest Rate Hedge	0.2	1.4
Estimate of Fair Value Measurement [Member]
Long-term debt:
Long-term Debt, Fair Value	2,039.9	2,346.3
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swap [Member]
Long-term debt:
Fair Value Adjustment to Interest Rate Hedge	0.2	1.4
Senior Notes [Member] \| Reported Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $400 Million 4.875% 2024 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	392.1	390.3
Senior Notes [Member] \| Reported Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $400 Million 5.90% 2020 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	0.0	88.6
Senior Notes [Member] \| Reported Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $500 Million 4.80% 2020 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	0.0	122.0
Senior Notes [Member] \| Reported Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $700 Million 4.875% 2021 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	123.8	138.0
Senior Notes [Member] \| Reported Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $316 Million 1.5% 2025 Senior Notes [Domain]
Long-term debt:
Long-term Debt, Fair Value	235.2	224.1
Senior Notes [Member] \| Reported Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $1.075 Billion 5.75% 2025 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	1,048.8	1,047.2
Senior Notes [Member] \| Reported Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $800 Million 6.25% 2040 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	292.8	292.6
Senior Notes [Member] \| Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $400 Million 4.875% 2024 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	370.2	398.0
Senior Notes [Member] \| Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $400 Million 5.90% 2020 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	0.0	88.0
Senior Notes [Member] \| Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $500 Million 4.80% 2020 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	0.0	118.8
Senior Notes [Member] \| Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $700 Million 4.875% 2021 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	122.3	130.8
Senior Notes [Member] \| Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $316 Million 1.5% 2025 Senior Notes [Domain]
Long-term debt:
Long-term Debt, Fair Value	352.4	352.9
Senior Notes [Member] \| Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $1.075 Billion 5.75% 2025 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	962.0	1,029.3
Senior Notes [Member] \| Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| $800 Million 6.25% 2040 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	232.8	227.1
Line of Credit [Member] \| Reported Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| ABL Facility [Member]
Long-term debt:
Long-term Debt, Fair Value	0.0	0.0
Line of Credit [Member] \| Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| ABL Facility [Member]
Long-term debt:
Long-term Debt, Fair Value	$ 0.0	$ 0.0