Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 5,464,502	$ 6,742,202	$ 17,457,112	$ 18,771,395
Earnings (loss) before income taxes and noncontrolling interests	380,339	922,502	1,604,577	2,352,115
Total assets	18,506,265		18,506,265		$ 17,920,588
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	3,244,473	4,401,610	10,897,322	12,151,843
Earnings (loss) before income taxes and noncontrolling interests	309,939	1,095,360	1,578,257	2,617,647
Total assets	9,117,610		9,117,610		9,244,086
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	1,820,359	1,849,218	5,225,064	5,056,299
Earnings (loss) before income taxes and noncontrolling interests	170,214	138,688	363,731	380,268
Total assets	4,730,410		4,730,410		4,734,636
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	399,670	491,374	1,334,726	1,563,253
Earnings (loss) before income taxes and noncontrolling interests	(10,599)	(29,074)	64,333	180,468
Total assets	3,225,367		3,225,367		3,492,126
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	825,237	1,055,093	2,542,008	3,019,199
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	57,517	56,185	174,718	142,862
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	2,063,167	2,923,196	6,917,523	8,687,408
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales	(2,945,921)	(4,034,474)	(9,634,249)	(11,849,469)
Earnings (loss) before income taxes and noncontrolling interests	(89,215)	$ (282,472)	(401,744)	$ (826,268)
Total assets	$ 1,432,878		$ 1,432,878		$ 449,740