SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Cash Flows) (Details) - USD ($)
$ in Millions |
9 Months Ended |
|
|
Sep. 30, 2018 |
Sep. 30, 2017 |
Dec. 31, 2017 |
Dec. 31, 2016 |
| Net cash provided (used) by operating activities |
$ 188.7
|
$ 206.7
|
Ìý
|
Ìý
|
| Purchase of property, plant and equipment |
(111.4)
|
(62.7)
|
Ìý
|
Ìý
|
| Deposits for property, plant and equipment |
(83.3)
|
(16.2)
|
Ìý
|
Ìý
|
| Intercompany investing |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Proceeds from Sale of Other Assets, Investing Activities |
18.5
|
2.2
|
Ìý
|
Ìý
|
| Proceeds on sales of assets |
2.5
|
(7.7)
|
Ìý
|
Ìý
|
| Net cash used by investing activities |
(173.7)
|
(84.4)
|
Ìý
|
Ìý
|
| Net proceeds from issuance of common shares |
0.0
|
661.3
|
Ìý
|
Ìý
|
| Proceeds from issuance of debt |
0.0
|
1,057.8
|
Ìý
|
Ìý
|
| Debt issuance costs |
(1.5)
|
(12.0)
|
Ìý
|
Ìý
|
| For the Nine Months Ended September 30, 2018 |
(16.3)
|
(1,720.7)
|
Ìý
|
Ìý
|
| Payments for Repurchase of Redeemable Noncontrolling Interest |
0.0
|
105.0
|
Ìý
|
Ìý
|
| Distributions of partnership equity |
(44.2)
|
(53.0)
|
Ìý
|
Ìý
|
| Intercompany financing |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Other financing activities |
(45.7)
|
(17.0)
|
Ìý
|
Ìý
|
| Net cash used by financing activities |
(107.7)
|
(188.6)
|
Ìý
|
Ìý
|
| EFFECT OF EXCHANGE RATE CHANGES ON CASH |
(2.3)
|
3.7
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(95.0)
|
(62.6)
|
Ìý
|
Ìý
|
| LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(13.8)
|
23.1
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(81.2)
|
(85.7)
|
Ìý
|
Ìý
|
| Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale |
897.1
|
227.1
|
$ 978.3
|
$ 312.8
|
| Reportable Legal Entities [Member] | Cliffs Shareholders Equity [Member] |
Ìý
|
Ìý
|
Ìý
|
Ìý
|
| Net cash provided (used) by operating activities |
(100.6)
|
(162.9)
|
Ìý
|
Ìý
|
| Purchase of property, plant and equipment |
(1.1)
|
(1.8)
|
Ìý
|
Ìý
|
| Deposits for property, plant and equipment |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Intercompany investing |
185.7
|
160.6
|
Ìý
|
Ìý
|
| Proceeds from Sale of Other Assets, Investing Activities |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Proceeds on sales of assets |
0.0
|
(7.7)
|
Ìý
|
Ìý
|
| Net cash used by investing activities |
184.6
|
151.1
|
Ìý
|
Ìý
|
| Net proceeds from issuance of common shares |
Ìý
|
661.3
|
Ìý
|
Ìý
|
| Proceeds from issuance of debt |
Ìý
|
1,057.8
|
Ìý
|
Ìý
|
| Debt issuance costs |
(1.5)
|
(12.0)
|
Ìý
|
Ìý
|
| For the Nine Months Ended September 30, 2018 |
(16.3)
|
(1,720.7)
|
Ìý
|
Ìý
|
| Payments for Repurchase of Redeemable Noncontrolling Interest |
Ìý
|
105.0
|
Ìý
|
Ìý
|
| Distributions of partnership equity |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Intercompany financing |
(120.7)
|
45.0
|
Ìý
|
Ìý
|
| Other financing activities |
(1.9)
|
(0.6)
|
Ìý
|
Ìý
|
| Net cash used by financing activities |
(140.4)
|
(74.2)
|
Ìý
|
Ìý
|
| EFFECT OF EXCHANGE RATE CHANGES ON CASH |
0.0
|
0.0
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(56.4)
|
(86.0)
|
Ìý
|
Ìý
|
| LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
0.0
|
0.0
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(56.4)
|
(86.0)
|
Ìý
|
Ìý
|
| Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale |
892.5
|
197.4
|
948.9
|
283.4
|
| Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] |
Ìý
|
Ìý
|
Ìý
|
Ìý
|
| Net cash provided (used) by operating activities |
425.6
|
293.9
|
Ìý
|
Ìý
|
| Purchase of property, plant and equipment |
(110.2)
|
(59.4)
|
Ìý
|
Ìý
|
| Deposits for property, plant and equipment |
(78.1)
|
(11.3)
|
Ìý
|
Ìý
|
| Intercompany investing |
(6.3)
|
(6.5)
|
Ìý
|
Ìý
|
| Proceeds from Sale of Other Assets, Investing Activities |
0.6
|
2.2
|
Ìý
|
Ìý
|
| Proceeds on sales of assets |
2.5
|
0.0
|
Ìý
|
Ìý
|
| Net cash used by investing activities |
(191.5)
|
(75.0)
|
Ìý
|
Ìý
|
| Net proceeds from issuance of common shares |
Ìý
|
0.0
|
Ìý
|
Ìý
|
| Proceeds from issuance of debt |
Ìý
|
0.0
|
Ìý
|
Ìý
|
| Debt issuance costs |
0.0
|
0.0
|
Ìý
|
Ìý
|
| For the Nine Months Ended September 30, 2018 |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Payments for Repurchase of Redeemable Noncontrolling Interest |
Ìý
|
0.0
|
Ìý
|
Ìý
|
| Distributions of partnership equity |
(44.2)
|
(53.0)
|
Ìý
|
Ìý
|
| Intercompany financing |
(188.6)
|
(162.2)
|
Ìý
|
Ìý
|
| Other financing activities |
(1.5)
|
(3.8)
|
Ìý
|
Ìý
|
| Net cash used by financing activities |
(234.3)
|
(219.0)
|
Ìý
|
Ìý
|
| EFFECT OF EXCHANGE RATE CHANGES ON CASH |
0.0
|
0.0
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(0.2)
|
(0.1)
|
Ìý
|
Ìý
|
| LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
0.0
|
0.0
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(0.2)
|
(0.1)
|
Ìý
|
Ìý
|
| Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale |
1.9
|
2.4
|
2.1
|
2.5
|
| Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member] |
Ìý
|
Ìý
|
Ìý
|
Ìý
|
| Net cash provided (used) by operating activities |
(136.3)
|
75.7
|
Ìý
|
Ìý
|
| Purchase of property, plant and equipment |
(0.1)
|
(1.5)
|
Ìý
|
Ìý
|
| Deposits for property, plant and equipment |
(5.2)
|
(4.9)
|
Ìý
|
Ìý
|
| Intercompany investing |
120.7
|
(45.0)
|
Ìý
|
Ìý
|
| Proceeds from Sale of Other Assets, Investing Activities |
17.9
|
0.0
|
Ìý
|
Ìý
|
| Proceeds on sales of assets |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Net cash used by investing activities |
133.3
|
(51.4)
|
Ìý
|
Ìý
|
| Net proceeds from issuance of common shares |
Ìý
|
0.0
|
Ìý
|
Ìý
|
| Proceeds from issuance of debt |
Ìý
|
0.0
|
Ìý
|
Ìý
|
| Debt issuance costs |
0.0
|
0.0
|
Ìý
|
Ìý
|
| For the Nine Months Ended September 30, 2018 |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Payments for Repurchase of Redeemable Noncontrolling Interest |
Ìý
|
0.0
|
Ìý
|
Ìý
|
| Distributions of partnership equity |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Intercompany financing |
9.2
|
8.1
|
Ìý
|
Ìý
|
| Other financing activities |
(42.3)
|
(12.6)
|
Ìý
|
Ìý
|
| Net cash used by financing activities |
(33.1)
|
(4.5)
|
Ìý
|
Ìý
|
| EFFECT OF EXCHANGE RATE CHANGES ON CASH |
(2.3)
|
3.7
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(38.4)
|
23.5
|
Ìý
|
Ìý
|
| LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(13.8)
|
(23.1)
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
(24.6)
|
0.4
|
Ìý
|
Ìý
|
| Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale |
2.7
|
27.3
|
27.3
|
26.9
|
| Consolidation, Eliminations [Member] |
Ìý
|
Ìý
|
Ìý
|
Ìý
|
| Net cash provided (used) by operating activities |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Purchase of property, plant and equipment |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Deposits for property, plant and equipment |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Intercompany investing |
(300.1)
|
(109.1)
|
Ìý
|
Ìý
|
| Proceeds from Sale of Other Assets, Investing Activities |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Proceeds on sales of assets |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Net cash used by investing activities |
(300.1)
|
(109.1)
|
Ìý
|
Ìý
|
| Net proceeds from issuance of common shares |
Ìý
|
0.0
|
Ìý
|
Ìý
|
| Proceeds from issuance of debt |
Ìý
|
0.0
|
Ìý
|
Ìý
|
| Debt issuance costs |
0.0
|
0.0
|
Ìý
|
Ìý
|
| For the Nine Months Ended September 30, 2018 |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Payments for Repurchase of Redeemable Noncontrolling Interest |
Ìý
|
0.0
|
Ìý
|
Ìý
|
| Distributions of partnership equity |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Intercompany financing |
300.1
|
109.1
|
Ìý
|
Ìý
|
| Other financing activities |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Net cash used by financing activities |
300.1
|
109.1
|
Ìý
|
Ìý
|
| EFFECT OF EXCHANGE RATE CHANGES ON CASH |
0.0
|
0.0
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
0.0
|
0.0
|
Ìý
|
Ìý
|
| LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
0.0
|
0.0
|
Ìý
|
Ìý
|
| DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS |
0.0
|
0.0
|
Ìý
|
Ìý
|
| Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale |
$ 0.0
|
$ 0.0
|
$ 0.0
|
$ 0.0
|