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

DEBT AND CREDIT FACILITIES (Schedule Of Long-Term Debt) (Details)

DEBT AND CREDIT FACILITIES (Schedule Of Long-Term Debt) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 19, 2017
Debt Instrument [Line Items]
Debt redemption premiums paid	$ 110,000,000	$ 17,400,000
Long-term Debt		2,192,600,000
Long-term Debt, Current Maturities		17,500,000
LONG-TERM DEBT	$ 2,304,200,000	$ 2,175,100,000
$400 Million 4.875% 2024 Senior Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Imputed interest rate	5.00%
Debt Instrument, Par Value	$ 400,000,000
Unamortized Debt Issuance Expense	(7,100,000)
Debt Instrument, Unamortized Discount	(2,600,000)
Long-term Debt	$ 390,300,000
$540 Million 8.25% 2020 First Lien Notes [Member]
Debt Instrument [Line Items]
Imputed interest rate		9.97%
Debt Instrument, Par Value		$ 540,000,000
Unamortized Debt Issuance Expense		(8,000,000)
Debt Instrument, Unamortized Discount		(25,700,000)
Long-term Debt		506,300,000
$218.5 Million 8.00% 2020 1.5 Lien Notes [Member]
Debt Instrument [Line Items]
Imputed interest rate	8.00%
Debt Instrument, Par Value		218,500,000
Unamortized Debt Issuance Expense		0
Debt Instrument, Unamortized Discount		(65,700,000)
Long-term Debt		$ 284,200,000
$544.2 Million 7.75% 2020 Second Lien Notes [Member]
Debt Instrument [Line Items]
Imputed interest rate		15.55%
Debt Instrument, Par Value		$ 430,100,000
Unamortized Debt Issuance Expense		(5,800,000)
Debt Instrument, Unamortized Discount		(85,200,000)
Long-term Debt		$ 339,100,000
$500 Million 3.95% 2018 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.95%
$400 Million 5.90% 2020 Senior Notes [Member]
Debt Instrument [Line Items]
Imputed interest rate	5.98%	5.98%
Debt Instrument, Par Value	$ 88,900,000	$ 225,600,000
Unamortized Debt Issuance Expense	(200,000)	(600,000)
Debt Instrument, Unamortized Discount	(100,000)	(500,000)
Long-term Debt	$ 88,600,000	$ 224,500,000
$500 Million 4.80% 2020 Senior Notes[Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.80%
Imputed interest rate	4.83%	4.83%
Debt Instrument, Par Value	$ 122,400,000	$ 236,800,000
Unamortized Debt Issuance Expense	(300,000)	(700,000)
Debt Instrument, Unamortized Discount	(100,000)	(200,000)
Long-term Debt	$ 122,000,000	$ 235,900,000
$700 Million 4.875% 2021 Senior Notes[Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Imputed interest rate	4.89%	4.89%
Debt Instrument, Par Value	$ 138,400,000	$ 309,400,000
Unamortized Debt Issuance Expense	(300,000)	(1,000,000)
Debt Instrument, Unamortized Discount	(100,000)	(200,000)
Long-term Debt	$ 138,000,000	$ 308,200,000
$316 Million 1.5% 2025 Senior Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.50%
Imputed interest rate	6.26%
Debt Instrument, Par Value	$ 316,300,000
Unamortized Debt Issuance Expense	(6,600,000)		$ (9,100,000)
Debt Instrument, Unamortized Discount	(85,600,000)
Long-term Debt	$ 224,100,000
$1.075 Billion 5.75% 2025 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.75%
Imputed interest rate	6.01%
Debt Instrument, Par Value	$ 1,075,000,000
Unamortized Debt Issuance Expense	(11,300,000)
Debt Instrument, Unamortized Discount	(16,500,000)
Long-term Debt	$ 1,047,200,000
$800 Million 6.25% 2040 Senior Notes [Member]
Debt Instrument [Line Items]
Imputed interest rate	6.34%	6.34%
Debt Instrument, Par Value	$ 298,400,000	$ 298,400,000
Unamortized Debt Issuance Expense	(2,400,000)	(2,500,000)
Debt Instrument, Unamortized Discount	(3,400,000)	(3,400,000)
Long-term Debt	292,600,000	292,500,000
ABL Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Par Value	550,000,000
Credit facility, amount outstanding	0	0
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Fair Value Adjustment to Interest Rate Hedge	$ 1,400,000	$ 1,900,000