Revenue - Schedule of Net Sales Disaggregates by Major Source (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2020	Jun. 29, 2019	Jul. 04, 2020	Jun. 29, 2019
Revenue from Contract with Customers [Line Items]
Revenues	$ 4,327,306	$ 5,895,986	$ 9,951,643	$ 11,992,610
Sheet [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,065,004	1,749,840	2,643,433	3,557,143
Bar [Member]
Revenue from Contract with Customers [Line Items]
Revenues	811,054	1,079,077	1,873,720	2,194,207
Structural [Member]
Revenue from Contract with Customers [Line Items]
Revenues	347,258	401,756	797,757	835,685
Plate [Member]
Revenue from Contract with Customers [Line Items]
Revenues	290,645	472,774	718,321	1,065,814
Tubular Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	250,311	293,321	555,368	623,192
Rebar Fabrication [Member]
Revenue from Contract with Customers [Line Items]
Revenues	413,916	438,677	837,232	780,732
Other Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	858,941	1,018,185	1,857,422	2,000,781
Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	290,177	442,356	668,390	935,056
Steel Mills [Member]
Revenue from Contract with Customers [Line Items]
Revenues	2,513,961	3,703,447	6,033,231	7,652,849
Steel Mills [Member] | Sheet [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,065,004	1,749,840	2,643,433	3,557,143
Steel Mills [Member] | Bar [Member]
Revenue from Contract with Customers [Line Items]
Revenues	811,054	1,079,077	1,873,720	2,194,207
Steel Mills [Member] | Structural [Member]
Revenue from Contract with Customers [Line Items]
Revenues	347,258	401,756	797,757	835,685
Steel Mills [Member] | Plate [Member]
Revenue from Contract with Customers [Line Items]
Revenues	290,645	472,774	718,321	1,065,814
Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,523,168	1,750,183	3,250,022	3,404,705
Steel Products [Member] | Tubular Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	250,311	293,321	555,368	623,192
Steel Products [Member] | Rebar Fabrication [Member]
Revenue from Contract with Customers [Line Items]
Revenues	413,916	438,677	837,232	780,732
Steel Products [Member] | Other Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	858,941	1,018,185	1,857,422	2,000,781
Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	290,177	442,356	668,390	935,056
Raw Materials [Member] | Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	$ 290,177	$ 442,356	$ 668,390	$ 935,056