DEBT AND CREDIT FACILITIES - Schedule of Extinguishment of Debt (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | |||||||
---|---|---|---|---|---|---|---|---|---|
Jun. 01, 2020 |
Apr. 24, 2020 |
Mar. 27, 2020 |
Mar. 13, 2020 |
Sep. 30, 2020 |
Jun. 30, 2020 |
Sep. 30, 2019 |
Sep. 30, 2020 |
Sep. 30, 2019 |
|
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | $ 736.4 | Ìý | Ìý | Ìý | Ìý | Ìý | $ 1,487.5 | $ 724.0 |
Reduction of Principal Long-Term Debt | Ìý | $ 181.2 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | $ 0.0 | Ìý | $ 0.0 | 132.6 | (18.2) |
Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | Ìý | Ìý | Ìý | $ 11.2 | Ìý | Ìý | Ìý |
7.625% 2021 AK Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | $ 8.5 | $ 364.2 | Ìý | Ìý | Ìý | 372.7 | Ìý |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 0.4 | Ìý |
7.50% 2023 AK Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | $ 56.5 | $ 310.7 | Ìý | Ìý | Ìý | 367.2 | Ìý |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 2.8 | Ìý |
4.875% 2024 Senior Secured Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 5.5 | Ìý |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 0.5 | Ìý |
6.375% 2025 Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 167.5 | Ìý |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 21.3 | Ìý |
1.50% 2025 Convertible Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 20.0 | Ìý |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 1.3 | Ìý |
4.875% 2021 Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 124.0 |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | (5.3) |
5.75% 2025 Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 77.1 | 600.0 |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 16.3 | $ (12.9) |
7.00% 2027 Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 247.3 | Ìý |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 28.4 | Ìý |
5.875% 2027 Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 194.5 | Ìý |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 48.7 | Ìý |
6.25% 2040 Senior Notes [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 35.7 | Ìý |
Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 12.9 | Ìý |
AK Steel Holding Corporation [Member] | Unsecured Industrial Revenue Bonds [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Extinguishment of Debt, Amount | $ 7.3 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |