Quarterly report pursuant to Section 13 or 15(d)

SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Cash Flows) (Details)

v3.19.1
SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Cash Flows) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Repurchase of common shares $ (124.3) $ 0.0    
Net cash provided (used) by operating activities (111.2) (142.9)    
Purchase of property, plant and equipment (132.7) (12.4)    
Deposits for property, plant and equipment (1.4) (59.0)    
Intercompany investing 0.0 0.0    
Other investing activities 8.5 0.0    
Net cash used by investing activities (125.6) (71.4)    
Dividends paid (14.8) 0.0    
Repurchase of debt (10.3) 0.0    
Intercompany financing 0.0 0.0    
Other financing activities (8.4) (7.0)    
Net cash used by financing activities (157.8) (7.0)    
EFFECT OF EXCHANGE RATE CHANGES ON CASH 0.0 0.2    
Increase/Decrease in Cash and Cash Equivalents, Including Cash Classified Within Other Current Assets Related to Discontinued Operations (394.6) (221.1)    
Increase/Decrease in Cash and Cash Equivalents from Discontinued Operations, Classified within Other Current Assets 1.6 0.0    
DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS (393.0) (221.1)    
Cash and cash equivalents 430.2 757.2 $ 823.2 $ 978.3
Reportable Legal Entities [Member] | Cliffs Shareholders Equity [Member]        
Repurchase of common shares (124.3)      
Net cash provided (used) by operating activities (71.6) (54.7)    
Purchase of property, plant and equipment (0.3) 0.0    
Deposits for property, plant and equipment 0.0 0.0    
Intercompany investing (157.6) (137.7)    
Other investing activities 0.0      
Net cash used by investing activities (157.9) (137.7)    
Dividends paid (14.8)      
Repurchase of debt (10.3)      
Intercompany financing 0.0 0.0    
Other financing activities (14.1) (2.9)    
Net cash used by financing activities (163.5) (2.9)    
EFFECT OF EXCHANGE RATE CHANGES ON CASH   0.0    
Increase/Decrease in Cash and Cash Equivalents, Including Cash Classified Within Other Current Assets Related to Discontinued Operations (393.0) (195.3)    
Increase/Decrease in Cash and Cash Equivalents from Discontinued Operations, Classified within Other Current Assets 0.0 0.0    
DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS (393.0) (195.3)    
Cash and cash equivalents 426.8 753.6 819.8 948.9
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]        
Repurchase of common shares 0.0      
Net cash provided (used) by operating activities (38.4) (64.7)    
Purchase of property, plant and equipment (132.4) (12.3)    
Deposits for property, plant and equipment (1.3) (54.4)    
Intercompany investing (0.4) (4.8)    
Other investing activities 8.4      
Net cash used by investing activities (125.7) (71.5)    
Dividends paid 0.0      
Repurchase of debt 0.0      
Intercompany financing 157.5 135.6    
Other financing activities 6.6 (0.5)    
Net cash used by financing activities 164.1 135.1    
EFFECT OF EXCHANGE RATE CHANGES ON CASH   0.0    
Increase/Decrease in Cash and Cash Equivalents, Including Cash Classified Within Other Current Assets Related to Discontinued Operations 0.0 (1.1)    
Increase/Decrease in Cash and Cash Equivalents from Discontinued Operations, Classified within Other Current Assets 0.0 0.0    
DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS 0.0 (1.1)    
Cash and cash equivalents 0.7 1.0 0.7 2.1
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]        
Repurchase of common shares 0.0      
Net cash provided (used) by operating activities (1.2) (23.5)    
Purchase of property, plant and equipment 0.0 (0.1)    
Deposits for property, plant and equipment (0.1) (4.6)    
Intercompany investing 0.0 0.0    
Other investing activities 0.1      
Net cash used by investing activities 0.0 (4.7)    
Dividends paid 0.0      
Repurchase of debt 0.0      
Intercompany financing 0.5 6.9    
Other financing activities (0.9) (3.6)    
Net cash used by financing activities (0.4) 3.3    
EFFECT OF EXCHANGE RATE CHANGES ON CASH   0.2    
Increase/Decrease in Cash and Cash Equivalents, Including Cash Classified Within Other Current Assets Related to Discontinued Operations (1.6) (24.7)    
Increase/Decrease in Cash and Cash Equivalents from Discontinued Operations, Classified within Other Current Assets 1.6 0.0    
DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS 0.0 (24.7)    
Cash and cash equivalents 2.7 2.6 2.7 27.3
Consolidation, Eliminations [Member]        
Repurchase of common shares 0.0      
Net cash provided (used) by operating activities 0.0 0.0    
Purchase of property, plant and equipment 0.0 0.0    
Deposits for property, plant and equipment 0.0 0.0    
Intercompany investing 158.0 142.5    
Other investing activities 0.0      
Net cash used by investing activities 158.0 142.5    
Dividends paid 0.0      
Repurchase of debt 0.0      
Intercompany financing (158.0) (142.5)    
Other financing activities 0.0 0.0    
Net cash used by financing activities (158.0) (142.5)    
EFFECT OF EXCHANGE RATE CHANGES ON CASH   0.0    
Increase/Decrease in Cash and Cash Equivalents, Including Cash Classified Within Other Current Assets Related to Discontinued Operations 0.0 0.0    
Increase/Decrease in Cash and Cash Equivalents from Discontinued Operations, Classified within Other Current Assets 0.0 0.0    
DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS 0.0 0.0    
Cash and cash equivalents $ 0.0 $ 0.0 $ 0.0 $ 0.0