Intangible Assets - Goodwill (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
Indefinite-lived Intangible Assets [Line Items]
Balance at December 31, 2020	$ 4
Additions	920
Balance at December 31, 2021	916
Flat-Rolled
Indefinite-lived Intangible Assets [Line Items]
Balance at December 31, 2020	0
Additions	0
Balance at December 31, 2021	0
Mini Mill (a)
Indefinite-lived Intangible Assets [Line Items]
Balance at December 31, 2020	0
Additions	916
Balance at December 31, 2021	916
USSE
Indefinite-lived Intangible Assets [Line Items]
Balance at December 31, 2020	4
Additions	4
Balance at December 31, 2021	0
Tubular
Indefinite-lived Intangible Assets [Line Items]
Balance at December 31, 2020	0
Additions	0
Balance at December 31, 2021	$ 0