Quarterly Information - Schedule of Quarterly Information (Unaudited) (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended						12 Months Ended
	Dec. 31, 2020	Oct. 03, 2020	Apr. 04, 2020	Dec. 31, 2019	Dec. 31, 2019	Mar. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information [Line Items]
Losses and impairments of assets							$ 613,640	$ 66,916	$ 110,000
Net benefit related to state tax credits	$ 39,700
Net benefit related to CARES Act carryback provision	48,200
Duferdofin Nucor S.r.l. [Member]
Quarterly Financial Information [Line Items]
Losses and impairments of assets	184,000		$ 287,800				483,500
Tax benefit related to investment	201,900
Aggregate Assets Impaired [Member]
Quarterly Financial Information [Line Items]
Impairment of assets	130,200				$ 66,900
Steel Products [Member]
Quarterly Financial Information [Line Items]
Restructuring charge		$ 16,400
Impairment of assets					11,900
Steel Mills [Member]
Quarterly Financial Information [Line Items]
Losses and impairments of assets	103,200			$ 20,000			$ 103,200	$ 20,000
Impairment of assets					20,000
Steel Mills [Member] | Inventory and Long-lived Assets [Member]
Quarterly Financial Information [Line Items]
Impairment of assets	103,200
Raw Materials [Member]
Quarterly Financial Information [Line Items]
Gain on the sale of an equity method investment						$ 33,700
Raw Materials [Member] | Unproved Natural Gas Well Assets [Member]
Quarterly Financial Information [Line Items]
Impairment of assets	$ 27,000
Raw Materials [Member] | Proved Producing Natural Gas Well Assets [Member]
Quarterly Financial Information [Line Items]
Impairment of assets					$ 35,000