Stock-Based Compensation - Summary of Nucor's RSU Activity (Detail) - Restricted Stock Units [Member] - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested at beginning of year, Shares	1,246	1,071	1,040
Granted, Shares	1,770	1,013	721
Vested, Shares	(1,207)	(827)	(677)
Canceled, Shares	(33)	(11)	(13)
Unvested at end of year, Shares	1,776	1,246	1,071
Unvested at beginning of year, Grant Date Fair Value	$ 59.09	$ 52.62	$ 48.47
Granted, Grant Date Fair Value	48.00	65.80	59.07
Vested, Grant Date Fair Value	52.43	58.98	53.17
Canceled, Grant Date Fair Value	57.09	55.02	50.21
Unvested at end of year, Grant Date Fair Value	$ 52.60	$ 59.09	$ 52.62