Quarterly report pursuant to Section 13 or 15(d)

DEBT AND CREDIT FACILITIES - Schedule of Extinguishment of Debt (Details)

v3.20.2
DEBT AND CREDIT FACILITIES - Schedule of Extinguishment of Debt (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Apr. 24, 2020
Mar. 27, 2020
Mar. 13, 2020
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount $ 736.4     $ 747.6 $ 714.0 $ 1,487.5 $ 724.0
Reduction of Principal Long-Term Debt $ 181.2            
Gain (loss) on extinguishment of debt       129.4 (17.9) 132.6 (18.2)
Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount       11.2      
7.625% 2021 AK Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount   $ 8.5 $ 364.2 0.0   372.7  
Gain (loss) on extinguishment of debt       0.0   0.4  
7.50% 2023 AK Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount   $ 56.5 $ 310.7 0.0   367.2  
Gain (loss) on extinguishment of debt       0.0   2.8  
4.875% 2024 Senior Secured Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount       5.5   5.5  
Gain (loss) on extinguishment of debt       0.5   0.5  
6.375% 2025 Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount       167.5   167.5  
Gain (loss) on extinguishment of debt       21.3   21.3  
1.50% 2025 Convertible Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount       20.0   20.0  
Gain (loss) on extinguishment of debt       1.3   1.3  
4.875% 2021 Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount         114.0   124.0
Gain (loss) on extinguishment of debt         (5.0)   (5.3)
5.75% 2025 Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount       77.1 600.0 77.1 600.0
Gain (loss) on extinguishment of debt       16.3 $ (12.9) 16.3 $ (12.9)
7.00% 2027 Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount       247.3   247.3  
Gain (loss) on extinguishment of debt       28.4   28.4  
5.875% 2027 Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount       194.5   194.5  
Gain (loss) on extinguishment of debt       48.7   48.7  
6.25% 2040 Senior Notes [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount       35.7   35.7  
Gain (loss) on extinguishment of debt       12.9   $ 12.9  
AK Steel Holding Corporation [Member] | Unsecured Industrial Revenue Bonds [Member]              
Extinguishment of Debt [Line Items]              
Extinguishment of Debt, Amount       $ 7.3