Fair Value of Financial Instruments - Additional Information (Details) - Stelco - Minntac Mine $ in Millions		8 Months Ended
	Apr. 30, 2020 USD ($) installment	Dec. 31, 2020 USD ($)
Business Acquisition [Line Items]
Noncontrolling Interest, Purchase Option, Interest In Investment Offered Under Option	25.00%
Noncontrolling Interest, Purchase Option, Aggregate Value Of Option		$ 100
Noncontrolling Interest, Purchase Option, Number Of Installments | installment	5
Noncontrolling Interest, Purchase Option, Installment Amount		$ 20
Noncontrolling Interest, Purchase Option, Additional Contribution Upon Exercise	$ 500