Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Oct. 03, 2020	Jul. 04, 2020	Apr. 04, 2020	Dec. 31, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 5,260,055	$ 4,927,960	$ 4,327,306	$ 5,624,337	$ 5,131,746	$ 5,464,502	$ 5,895,986	$ 6,096,624	$ 20,139,658	$ 22,588,858	$ 25,067,279
Depreciation expense									702,110	648,911	630,879
Amortization expense									83,356	85,742	88,758
Earnings (loss) before income taxes and noncontrolling interests									835,538	1,782,807	3,229,391
Total assets	20,125,394				18,344,666				20,125,394	18,344,666	17,920,588
Capital expenditures									1,527,116	1,512,070	997,256
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales									12,109,307	13,933,950	16,245,218
Depreciation expense									449,290	401,609	378,146
Amortization expense									7,334	8,624	9,400
Earnings (loss) before income taxes and noncontrolling interests									720,151	1,790,694	3,500,085
Total assets	9,708,260				9,283,216				9,708,260	9,283,216	9,244,086
Capital expenditures									1,238,132	1,133,089	720,310
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales									6,623,068	6,990,064	6,796,501
Depreciation expense									93,184	85,276	80,681
Amortization expense									47,773	49,914	51,997
Earnings (loss) before income taxes and noncontrolling interests									690,547	511,145	467,105
Total assets	4,461,042				4,610,628				4,461,042	4,610,628	4,734,636
Capital expenditures									135,511	93,848	88,585
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales									1,407,283	1,664,844	2,025,560
Depreciation expense									150,474	151,124	161,666
Amortization expense									28,249	27,204	27,361
Earnings (loss) before income taxes and noncontrolling interests									23,621	(28,244)	236,241
Total assets	3,324,489				3,316,479				3,324,489	3,316,479	3,492,126
Capital expenditures									125,213	244,818	169,926
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales									3,036,790	3,304,437	3,924,160
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales									248,477	233,728	207,003
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales									8,153,841	8,784,397	11,460,645
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales									(11,439,108)	(12,322,562)	(15,591,808)
Earnings (loss) before income taxes and noncontrolling interests									(598,781)	(490,788)	(974,040)
Total assets	$ 2,631,603				$ 1,134,343				2,631,603	1,134,343	449,740
Corporate [Member]
Segment Reporting Information [Line Items]
Depreciation expense									9,163	10,902	10,386
Capital expenditures									$ 28,259	$ 40,315	$ 18,435