Revenue - Schedule of Net Sales Disaggregates by Major Source (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 29, 2018	Sep. 29, 2018
Revenue from Contract with Customers [Line Items]
Revenues	$ 6,742,202	$ 18,771,395
Sheet [Member]
Revenue from Contract with Customers [Line Items]
Revenues	2,051,634	5,692,281
Bar [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,243,890	3,592,475
Structural [Member]
Revenue from Contract with Customers [Line Items]
Revenues	503,733	1,348,987
Plate [Member]
Revenue from Contract with Customers [Line Items]
Revenues	602,353	1,518,100
Tubular Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	357,815	1,040,611
Rebar Fabrication [Member]
Revenue from Contract with Customers [Line Items]
Revenues	412,977	1,133,117
Other Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,078,426	2,882,571
Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	491,374	1,563,253
Steel Mills [Member]
Revenue from Contract with Customers [Line Items]
Revenues	4,401,610	12,151,843
Steel Mills [Member] | Sheet [Member]
Revenue from Contract with Customers [Line Items]
Revenues	2,051,634	5,692,281
Steel Mills [Member] | Bar [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,243,890	3,592,475
Steel Mills [Member] | Structural [Member]
Revenue from Contract with Customers [Line Items]
Revenues	503,733	1,348,987
Steel Mills [Member] | Plate [Member]
Revenue from Contract with Customers [Line Items]
Revenues	602,353	1,518,100
Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,849,218	5,056,299
Steel Products [Member] | Tubular Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	357,815	1,040,611
Steel Products [Member] | Rebar Fabrication [Member]
Revenue from Contract with Customers [Line Items]
Revenues	412,977	1,133,117
Steel Products [Member] | Other Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,078,426	2,882,571
Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	491,374	1,563,253
Raw Materials [Member] | Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	$ 491,374	$ 1,563,253