Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 6,096,624	$ 5,568,419
Earnings (loss) before income taxes and noncontrolling interests	689,616	515,912
Total assets	18,086,698		$ 17,920,588
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	3,949,402	3,580,694
Earnings (loss) before income taxes and noncontrolling interests	689,398	560,503
Total assets	9,135,256		9,244,086
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	1,654,522	1,468,711
Earnings (loss) before income taxes and noncontrolling interests	77,433	85,814
Total assets	4,774,332		4,734,636
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	492,700	519,014
Earnings (loss) before income taxes and noncontrolling interests	53,223	74,547
Total assets	3,405,968		3,492,126
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	902,224	898,326
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	62,805	35,770
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	2,423,869	2,608,944
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales	(3,388,898)	(3,543,040)
Earnings (loss) before income taxes and noncontrolling interests	(130,438)	$ (204,952)
Total assets	$ 771,142		$ 449,740