Stock-Based Compensation - Summary of Nucor's RSU Activity (Detail) - Restricted Stock Units [Member] - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested at beginning of year, Shares	1,776	1,246	1,071
Granted, Shares	1,246	1,770	1,013
Vested, Shares	(1,166)	(1,207)	(827)
Canceled, Shares	(26)	(33)	(11)
Unvested at end of year, Shares	1,830	1,776	1,246
Unvested at beginning of year, Grant Date Fair Value	$ 52.60	$ 59.09	$ 52.62
Granted, Grant Date Fair Value	42.46	48.00	65.80
Vested, Grant Date Fair Value	50.10	52.43	58.98
Canceled, Grant Date Fair Value	49.75	57.09	55.02
Unvested at end of year, Grant Date Fair Value	$ 47.33	$ 52.60	$ 59.09