SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Operations and Comprehensive Income (Loss) (Details) - USD ($) $ in Millions |
3 Months Ended |
12 Months Ended |
Dec. 31, 2019 |
Sep. 30, 2019 |
Jun. 30, 2019 |
Mar. 31, 2019 |
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Revenues from product sales and services |
$ 534.1
|
$ 555.6
|
$ 743.2
|
$ 157.0
|
$ 696.3
|
$ 741.8
|
$ 714.3
|
$ 180.0
|
$ 1,989.9
|
$ 2,332.4
|
$ 1,866.0
|
Cost of goods sold and operating expenses |
|
|
|
|
|
|
|
|
(1,414.2)
|
(1,522.8)
|
(1,398.4)
|
Sales margin |
$ 126.9
|
$ 154.9
|
$ 263.0
|
$ 30.9
|
$ 202.0
|
$ 261.6
|
$ 284.5
|
$ 61.5
|
575.7
|
809.6
|
467.6
|
Other operating income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Selling, general and administrative expenses |
|
|
|
|
|
|
|
|
(119.4)
|
(113.5)
|
(102.9)
|
Miscellaneous - net |
|
|
|
|
|
|
|
|
(27.0)
|
(22.9)
|
25.5
|
Total other operating expense |
|
|
|
|
|
|
|
|
(146.4)
|
(136.4)
|
(77.4)
|
Operating income (loss) |
|
|
|
|
|
|
|
|
429.3
|
673.2
|
390.2
|
Other income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Interest income (expense), net |
|
|
|
|
|
|
|
|
(101.2)
|
(118.9)
|
(126.8)
|
Loss on extinguishment of debt |
|
|
|
|
|
|
|
|
(18.2)
|
(6.8)
|
(165.4)
|
Other non-operating income |
|
|
|
|
|
|
|
|
2.2
|
17.2
|
10.2
|
Total other expense |
|
|
|
|
|
|
|
|
(117.2)
|
(108.5)
|
(282.0)
|
Income (loss) from continuing operations before income taxes |
|
|
|
|
|
|
|
|
312.1
|
564.7
|
108.2
|
Income tax benefit (expense) |
|
|
|
|
|
|
|
|
(17.6)
|
475.2
|
252.4
|
Equity in income of subsidiaries |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Income from continuing operations |
|
|
|
|
|
|
|
|
294.5
|
1,039.9
|
360.6
|
Income (loss) from discontinued operations, net of tax |
|
|
|
|
|
|
|
|
(1.7)
|
88.2
|
2.5
|
Net income |
|
|
|
|
|
|
|
|
292.8
|
1,128.1
|
363.1
|
Net Income (Loss) Attributable to Noncontrolling Interest |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
(3.9)
|
Net income attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
292.8
|
1,128.1
|
367.0
|
Other comprehensive income (loss) |
|
|
|
|
|
|
|
|
(34.9)
|
(244.9)
|
(4.0)
|
Total comprehensive income (loss) attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
257.9
|
883.2
|
363.0
|
Consolidation, Eliminations [Member] |
|
|
|
|
|
|
|
|
|
|
|
Revenues from product sales and services |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Cost of goods sold and operating expenses |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Sales margin |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Other operating income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Selling, general and administrative expenses |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Miscellaneous - net |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Total other operating expense |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Operating income (loss) |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Other income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Interest income (expense), net |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Loss on extinguishment of debt |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Other non-operating income |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Total other expense |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Income (loss) from continuing operations before income taxes |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Income tax benefit (expense) |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Equity in income of subsidiaries |
|
|
|
|
|
|
|
|
(549.9)
|
(883.7)
|
(524.4)
|
Income from continuing operations |
|
|
|
|
|
|
|
|
(549.9)
|
(883.7)
|
(524.4)
|
Income (loss) from discontinued operations, net of tax |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Net income |
|
|
|
|
|
|
|
|
|
|
(524.4)
|
Net Income (Loss) Attributable to Noncontrolling Interest |
|
|
|
|
|
|
|
|
|
|
0.0
|
Net income attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
(549.9)
|
(883.7)
|
(524.4)
|
Other comprehensive income (loss) |
|
|
|
|
|
|
|
|
18.9
|
280.8
|
(8.1)
|
Total comprehensive income (loss) attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
(531.0)
|
(602.9)
|
(532.5)
|
Parent [Member] | Reportable Legal Entities [Member] |
|
|
|
|
|
|
|
|
|
|
|
Revenues from product sales and services |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Cost of goods sold and operating expenses |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Sales margin |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Other operating income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Selling, general and administrative expenses |
|
|
|
|
|
|
|
|
(100.7)
|
(86.1)
|
(77.2)
|
Miscellaneous - net |
|
|
|
|
|
|
|
|
0.1
|
(0.3)
|
(2.3)
|
Total other operating expense |
|
|
|
|
|
|
|
|
(100.6)
|
(86.4)
|
(79.5)
|
Operating income (loss) |
|
|
|
|
|
|
|
|
(100.6)
|
(86.4)
|
(79.5)
|
Other income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Interest income (expense), net |
|
|
|
|
|
|
|
|
(99.4)
|
(117.6)
|
(126.8)
|
Loss on extinguishment of debt |
|
|
|
|
|
|
|
|
(18.2)
|
(6.8)
|
(165.4)
|
Other non-operating income |
|
|
|
|
|
|
|
|
(4.0)
|
(3.5)
|
(4.0)
|
Total other expense |
|
|
|
|
|
|
|
|
(121.6)
|
(127.9)
|
(296.2)
|
Income (loss) from continuing operations before income taxes |
|
|
|
|
|
|
|
|
(222.2)
|
(214.3)
|
(375.7)
|
Income tax benefit (expense) |
|
|
|
|
|
|
|
|
(17.0)
|
474.7
|
251.4
|
Equity in income of subsidiaries |
|
|
|
|
|
|
|
|
531.6
|
858.2
|
512.6
|
Income from continuing operations |
|
|
|
|
|
|
|
|
292.4
|
1,118.6
|
388.3
|
Income (loss) from discontinued operations, net of tax |
|
|
|
|
|
|
|
|
0.4
|
9.5
|
(21.3)
|
Net income |
|
|
|
|
|
|
|
|
|
|
367.0
|
Net Income (Loss) Attributable to Noncontrolling Interest |
|
|
|
|
|
|
|
|
|
|
0.0
|
Net income attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
292.8
|
1,128.1
|
367.0
|
Other comprehensive income (loss) |
|
|
|
|
|
|
|
|
(34.9)
|
(244.9)
|
(4.0)
|
Total comprehensive income (loss) attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
257.9
|
883.2
|
363.0
|
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] |
|
|
|
|
|
|
|
|
|
|
|
Revenues from product sales and services |
|
|
|
|
|
|
|
|
1,989.9
|
2,332.4
|
1,866.0
|
Cost of goods sold and operating expenses |
|
|
|
|
|
|
|
|
(1,414.2)
|
(1,522.8)
|
(1,398.4)
|
Sales margin |
|
|
|
|
|
|
|
|
575.7
|
809.6
|
467.6
|
Other operating income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Selling, general and administrative expenses |
|
|
|
|
|
|
|
|
(18.3)
|
(27.1)
|
(19.9)
|
Miscellaneous - net |
|
|
|
|
|
|
|
|
(26.0)
|
(26.9)
|
11.0
|
Total other operating expense |
|
|
|
|
|
|
|
|
(44.3)
|
(54.0)
|
(8.9)
|
Operating income (loss) |
|
|
|
|
|
|
|
|
531.4
|
755.6
|
458.7
|
Other income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Interest income (expense), net |
|
|
|
|
|
|
|
|
(2.3)
|
(2.1)
|
(1.0)
|
Loss on extinguishment of debt |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Other non-operating income |
|
|
|
|
|
|
|
|
(12.9)
|
0.9
|
(3.0)
|
Total other expense |
|
|
|
|
|
|
|
|
(15.2)
|
(1.2)
|
(4.0)
|
Income (loss) from continuing operations before income taxes |
|
|
|
|
|
|
|
|
516.2
|
754.4
|
454.7
|
Income tax benefit (expense) |
|
|
|
|
|
|
|
|
(0.4)
|
0.0
|
1.3
|
Equity in income of subsidiaries |
|
|
|
|
|
|
|
|
18.3
|
25.5
|
11.8
|
Income from continuing operations |
|
|
|
|
|
|
|
|
534.1
|
779.9
|
467.8
|
Income (loss) from discontinued operations, net of tax |
|
|
|
|
|
|
|
|
(0.3)
|
12.3
|
1.7
|
Net income |
|
|
|
|
|
|
|
|
|
|
469.5
|
Net Income (Loss) Attributable to Noncontrolling Interest |
|
|
|
|
|
|
|
|
|
|
(3.9)
|
Net income attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
533.8
|
792.2
|
473.4
|
Other comprehensive income (loss) |
|
|
|
|
|
|
|
|
(35.8)
|
(24.1)
|
12.9
|
Total comprehensive income (loss) attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
498.0
|
768.1
|
486.3
|
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] |
|
|
|
|
|
|
|
|
|
|
|
Revenues from product sales and services |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Cost of goods sold and operating expenses |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Sales margin |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Other operating income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Selling, general and administrative expenses |
|
|
|
|
|
|
|
|
(0.4)
|
(0.3)
|
(5.8)
|
Miscellaneous - net |
|
|
|
|
|
|
|
|
(1.1)
|
4.3
|
16.8
|
Total other operating expense |
|
|
|
|
|
|
|
|
(1.5)
|
4.0
|
11.0
|
Operating income (loss) |
|
|
|
|
|
|
|
|
(1.5)
|
4.0
|
11.0
|
Other income (expense): |
|
|
|
|
|
|
|
|
|
|
|
Interest income (expense), net |
|
|
|
|
|
|
|
|
0.5
|
0.8
|
1.0
|
Loss on extinguishment of debt |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Other non-operating income |
|
|
|
|
|
|
|
|
19.1
|
19.8
|
17.2
|
Total other expense |
|
|
|
|
|
|
|
|
19.6
|
20.6
|
18.2
|
Income (loss) from continuing operations before income taxes |
|
|
|
|
|
|
|
|
18.1
|
24.6
|
29.2
|
Income tax benefit (expense) |
|
|
|
|
|
|
|
|
(0.2)
|
0.5
|
(0.3)
|
Equity in income of subsidiaries |
|
|
|
|
|
|
|
|
0.0
|
0.0
|
0.0
|
Income from continuing operations |
|
|
|
|
|
|
|
|
17.9
|
25.1
|
28.9
|
Income (loss) from discontinued operations, net of tax |
|
|
|
|
|
|
|
|
(1.8)
|
66.4
|
22.1
|
Net income |
|
|
|
|
|
|
|
|
|
|
51.0
|
Net Income (Loss) Attributable to Noncontrolling Interest |
|
|
|
|
|
|
|
|
|
|
0.0
|
Net income attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
16.1
|
91.5
|
51.0
|
Other comprehensive income (loss) |
|
|
|
|
|
|
|
|
16.9
|
(256.7)
|
(4.8)
|
Total comprehensive income (loss) attributable to Cliffs shareholders |
|
|
|
|
|
|
|
|
$ 33.0
|
$ (165.2)
|
$ 46.2
|