Debt - Debt Redemption Percentages (Details)	Feb. 11, 2021	Sep. 18, 2020	Sep. 10, 2020	May 31, 2019
Big River Steel Environmental Revenue Bonds - Series 2020
Debt Instrument, Redemption [Line Items]
Redemption price			100.00%
Condition 1 | 2029 Senior Notes | Period One
Debt Instrument, Redemption [Line Items]
Redemption price	100.00%
Condition 1 | 2029 Senior Notes | Period Two
Debt Instrument, Redemption [Line Items]
Redemption price	103.438%
Condition 1 | 2029 Senior Notes | Period Three
Debt Instrument, Redemption [Line Items]
Redemption price	101.719%
Condition 1 | 2029 Senior Notes | Period Four
Debt Instrument, Redemption [Line Items]
Redemption price	100.00%
Condition 1 | 2029 Senior Secured Notes | Period One
Debt Instrument, Redemption [Line Items]
Redemption price		103.313%
Condition 1 | 2029 Senior Secured Notes | Period Two
Debt Instrument, Redemption [Line Items]
Redemption price		101.656%
Condition 1 | 2029 Senior Secured Notes | Period Three
Debt Instrument, Redemption [Line Items]
Redemption price		100.00%
Condition 1 | Big River Steel Environmental Revenue Bonds - Series 2019 | Period One
Debt Instrument, Redemption [Line Items]
Redemption price				103.00%
Condition 1 | Big River Steel Environmental Revenue Bonds - Series 2019 | Period Two
Debt Instrument, Redemption [Line Items]
Redemption price				102.00%
Condition 1 | Big River Steel Environmental Revenue Bonds - Series 2019 | Period Three
Debt Instrument, Redemption [Line Items]
Redemption price				101.00%
Condition 1 | Big River Steel Environmental Revenue Bonds - Series 2019 | Period Four
Debt Instrument, Redemption [Line Items]
Redemption price				100.00%
Condition 1 | Big River Steel Environmental Revenue Bonds - Series 2020 | Period One
Debt Instrument, Redemption [Line Items]
Redemption price			103.00%
Condition 1 | Big River Steel Environmental Revenue Bonds - Series 2020 | Period Two
Debt Instrument, Redemption [Line Items]
Redemption price			102.00%
Condition 1 | Big River Steel Environmental Revenue Bonds - Series 2020 | Period Three
Debt Instrument, Redemption [Line Items]
Redemption price			101.00%
Condition 1 | Big River Steel Environmental Revenue Bonds - Series 2020 | Period Four
Debt Instrument, Redemption [Line Items]
Redemption price			100.00%