Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 5,895,986	$ 6,460,774	$ 11,992,610	$ 12,029,193
Earnings (loss) before income taxes and noncontrolling interests	534,622	913,701	1,224,238	1,429,613
Total assets	18,126,480		18,126,480		$ 17,920,588
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	3,703,447	4,169,539	7,652,849	7,750,233
Earnings (loss) before income taxes and noncontrolling interests	578,920	961,784	1,268,318	1,522,287
Total assets	9,204,020		9,204,020		9,244,086
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	1,750,183	1,738,370	3,404,705	3,207,081
Earnings (loss) before income taxes and noncontrolling interests	116,084	155,766	193,517	241,580
Total assets	4,770,901		4,770,901		4,734,636
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	442,356	552,865	935,056	1,071,879
Earnings (loss) before income taxes and noncontrolling interests	21,709	134,995	74,932	209,542
Total assets	3,259,940		3,259,940		3,492,126
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	814,548	1,065,780	1,716,771	1,964,106
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	54,396	50,907	117,201	86,677
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	2,430,487	3,155,268	4,854,356	5,764,212
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales	(3,299,431)	(4,271,955)	(6,688,328)	(7,814,995)
Earnings (loss) before income taxes and noncontrolling interests	(182,091)	$ (338,844)	(312,529)	$ (543,796)
Total assets	$ 891,619		$ 891,619		$ 449,740