Intangible Contract Assets and Liabilities Textuals (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2017	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 01, 2017
Coal supply agreements
Coal Supply Agreements
Amortization of Intangible Assets	$ 121.3
Fresh Start Reporting [Member] | Coal supply agreements
Finite-Lived Intangible Assets [Line Items]
Intangible Assets							$ 314.9
Liabilities							58.7
Intangible Liabilities							$ 116.2
Successor
Finite-Lived Intangible Assets [Line Items]
Liabilities	4,525.4
Successor | Take Or Pay Contracts
Take-or-Pay Contracts
Amortization Of Intangible Liabilities	$ 22.5
Scenario, Forecast | Take Or Pay Contracts
Take-or-Pay Contracts
Finite-Lived Intangible Liabilities, Amortization Expense, Next Twelve Months						$ 30.0
Finite-Lived Intangible Liabilities, Amortization Expense, Year Two					$ 20.0
Finite-Lived Intangible Liabilities, Amortization Expense, Year Three				$ 10.0
Finite-Lived Intangible Liabilities, Amortization Expense, Year Four			$ 5.0
Finite-Lived Intangible Liabilities, Amortization Expense, Year Five		$ 5.0
Scenario, Forecast | Coal supply agreements
Coal Supply Agreements
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months						100.0
Finite-Lived Intangible Assets, Amortization Expense, Year Two						$ 25.0
Finite-Lived Intangible Assets, Amortization Expense, Year Three					$ 7.0
Finite-Lived Intangible Assets, Amortization Expense, Year Four				$ 1.0
Finite-Lived Intangible Assets, Amortization Expense, Year Five		$ 1.0