Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2015	Jul. 05, 2014	Jul. 04, 2015	Jul. 05, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net sales	$ 4,357,609	$ 5,291,075	$ 8,757,049	$ 10,399,519
Earnings (loss) before income taxes and noncontrolling interests	216,222	241,865	335,267	449,366
Total assets	15,068,177		15,068,177		$ 15,615,927
Steel Mills [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes and noncontrolling interests	198,500	368,138	415,628	685,935
Total assets	7,900,573		7,900,573		8,528,623
Steel Products [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes and noncontrolling interests	70,636	42,612	103,094	44,332
Total assets	2,708,522		2,708,522		2,731,320
Raw Materials [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes and noncontrolling interests	(38,104)	(9,635)	(79,601)	(1,276)
Total assets	3,590,917		3,590,917		3,858,254
Net Sales to External Customers [Member]
Segment Reporting Information [Line Items]
Net sales	4,357,609	5,291,075	8,757,049	10,399,519
Net Sales to External Customers [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	2,968,644	3,674,140	6,021,983	7,281,904
Net Sales to External Customers [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	1,015,646	1,035,923	1,937,030	1,910,092
Net Sales to External Customers [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	373,319	581,012	798,036	1,207,523
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	577,271	742,200	1,152,254	1,451,066
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	21,020	26,542	40,517	48,042
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	1,687,941	2,443,492	3,520,859	4,971,498
Intercompany Eliminations [Member] | Corporate/Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales	(2,286,232)	(3,212,234)	(4,713,630)	(6,470,606)
Earnings (loss) before income taxes and noncontrolling interests	(14,810)	$ (159,250)	(103,854)	$ (279,625)
Total assets	$ 868,165		$ 868,165		$ 497,730