Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 03, 2020	Sep. 28, 2019	Oct. 03, 2020	Sep. 28, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net sales	$ 4,927,960	$ 5,464,502	$ 14,879,603	$ 17,457,112
Earnings (loss) before income taxes and noncontrolling interests	290,418	380,339	617,772	1,604,577
Total assets	19,519,277		19,519,277		$ 18,344,666
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	2,842,625	3,244,473	8,875,856	10,897,322
Earnings (loss) before income taxes and noncontrolling interests	205,152	309,939	512,082	1,578,257
Total assets	9,251,790		9,251,790		9,283,216
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	1,738,004	1,820,359	4,988,026	5,225,064
Earnings (loss) before income taxes and noncontrolling interests	186,976	170,214	502,409	363,731
Total assets	4,399,501		4,399,501		4,610,628
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	347,331	399,670	1,015,721	1,334,726
Earnings (loss) before income taxes and noncontrolling interests	6,232	(10,599)	(3,068)	64,333
Total assets	3,172,464		3,172,464		3,316,479
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	731,942	825,237	2,264,278	2,542,008
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	51,029	57,517	197,603	174,718
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	1,863,796	2,063,167	5,772,583	6,917,523
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales	(2,646,767)	(2,945,921)	(8,234,464)	(9,634,249)
Earnings (loss) before income taxes and noncontrolling interests	(107,942)	$ (89,215)	(393,651)	$ (401,744)
Total assets	$ 2,695,522		$ 2,695,522		$ 1,134,343