Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 6,742,202	$ 5,170,117	$ 18,771,395	$ 15,160,065
Earnings (loss) before income taxes and noncontrolling interests	922,502	370,605	2,352,115	1,427,716
Total assets	17,962,893		17,962,893		$ 15,841,258
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	4,401,610	3,214,921	12,151,843	9,809,492
Earnings (loss) before income taxes and noncontrolling interests	1,095,360	405,097	2,617,647	1,628,800
Total assets	8,764,717		8,764,717		7,671,217
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	1,849,218	1,514,086	5,056,299	4,093,136
Earnings (loss) before income taxes and noncontrolling interests	138,688	86,908	380,268	237,463
Total assets	4,828,354		4,828,354		4,323,907
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	491,374	441,110	1,563,253	1,257,437
Earnings (loss) before income taxes and noncontrolling interests	(29,074)	9,957	180,468	102,575
Total assets	3,318,424		3,318,424		3,396,110
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales	(4,034,474)	(3,129,645)	(11,849,469)	(9,241,606)
Earnings (loss) before income taxes and noncontrolling interests	(282,472)	(131,357)	(826,268)	(541,122)
Total assets	1,051,398		1,051,398		$ 450,024
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	1,055,093	764,977	3,019,199	2,182,582
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	56,185	30,828	142,862	87,193
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	$ 2,923,196	$ 2,333,840	$ 8,687,408	$ 6,971,831