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Transactions with Related Parties - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 15, 2021	Feb. 29, 2020
Related Party Transaction [Line Items]
Related party sales and service transactions	$ 1,311	$ 976	$ 1,431
Accounts payable to related parties	99	105
PRO-TEC Coating Company, LLC
Related Party Transaction [Line Items]
Accounts payable to related parties	98	86
Other related parties
Related Party Transaction [Line Items]
Accounts payable to related parties	1	19
Outside processing services
Related Party Transaction [Line Items]
Purchases from related parties	38	90	31
Taconite pellets
Related Party Transaction [Line Items]
Purchases from related parties	$ 111	$ 78	$ 104
Big River Steel
Related Party Transaction [Line Items]
Due from related parties				$ 27
UPI
Related Party Transaction [Line Items]
Due to related parties					$ 135