Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Apr. 01, 2017	Apr. 02, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net sales	$ 4,815,179	$ 3,715,576
Earnings (loss) before income taxes and noncontrolling interests	548,975	169,563
Total assets	15,875,460		$ 15,223,518
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	3,542,789	2,634,589
Earnings (loss) before income taxes and noncontrolling interests	684,161	280,372
Total assets	9,054,369		8,084,773
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	860,075	828,376
Earnings (loss) before income taxes and noncontrolling interests	26,922	42,367
Total assets	2,596,029		2,544,344
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	412,315	252,611
Earnings (loss) before income taxes and noncontrolling interests	26,391	(63,372)
Total assets	3,395,099		3,235,237
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales	(2,866,700)	(1,662,831)
Earnings (loss) before income taxes and noncontrolling interests	(188,499)	(89,804)
Total assets	829,963		$ 1,359,164
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	660,918	470,263
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	27,143	21,206
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	$ 2,178,639	$ 1,171,362