SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
Oct. 03, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements for Cornerstone Building Brands, Inc. (together with its subsidiaries, unless otherwise indicated, the “Company,” “Cornerstone,” “NCI”, “we,” “us” or “our”) have been prepared in accordance with generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by generally accepted accounting principles (“GAAP”) for complete financial statements. In the opinion of management, the unaudited consolidated financial statements included herein contain all adjustments, which consist of normal recurring adjustments, necessary to fairly present the Company’s financial position, results of operations and cash flows for the periods indicated. Operating results for the period from January 1, 2020 through October 3, 2020 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2020. Certain reclassifications have been made to the prior period disaggregated revenue amounts in the notes to the consolidated financial statements to conform to the current presentation. The net effect of these reclassifications was not material to the consolidated financial statements (see disaggregated revenue table below).
Reporting Periods	Reporting Periods The Company’s current fiscal quarters are based on a four-four-five week calendar with periods ending on the Saturday of the last week in the quarter except that December 31st will always be the year-end date. Therefore, the financial results of certain fiscal quarters may not be comparable to prior fiscal quarters.
Accounts Receivables and Related Allowance	Accounts Receivables and Related Allowance The Company reports accounts receivable net of the allowance for expected credit losses. Trade accounts receivable are the result of sales of metal building products, insulated metal panels, metal coating, vinyl siding, metal siding, injection molded products, vinyl windows, aluminum windows, and other products and services to customers throughout the United States and Canada and affiliated territories, including international builders who resell to end users. Sales are primarily denominated in U.S. dollars. Credit sales do not normally require a pledge of collateral; however, various types of liens may be filed to enhance the collection process and we require payment prior to shipment for certain international shipments. The Company establishes reserves for doubtful accounts on a customer by customer basis when we believe the required payment of specific amounts owed is unlikely to occur. Bad debt provisions are included in selling, general and administrative expenses. In establishing these reserves, the Company considers changes in the financial position of a customer, availability of security, unusual macroeconomic conditions, lien rights and bond rights as well as disputes, if any, with our customers. Our allowance for doubtful accounts reflects reserves for customer receivables to reduce receivables to amounts expected to be collected. We determine past due status as of the contractual payment date. Interest on delinquent accounts receivable is included in the trade accounts receivable balance and recognized as interest income when earned and collectability is reasonably assured. Uncollectible accounts are written off when a settlement is reached for an amount that is less than the outstanding historical balance, all collection efforts have been exhausted and/or any legal action taken by the Company has concluded.
Net Sales	Net Sales The Company adopted Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), as of October 29, 2018. ASU 2014-09 provides enhancements to the quality and consistency of how revenue is reported while also improving comparability in the financial statements of companies reporting using International Financial Reporting Standards and GAAP. The core principle of this update is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The Company enters into contracts that pertain to products, which are accounted for as separate performance obligations and are typically one year or less in duration. The Company does not exercise significant judgment in determining the timing for the satisfaction of performance obligations or the transaction price. Revenue is measured as the amount of consideration expected to be received in exchange for our products. The Company has elected to apply the practical expedient provided for in ASU No. 2014-09 and has not disclosed information regarding remaining performance obligations that have original expected durations of one year or less. Revenue is generally recognized when the product has shipped from our facility and control has transferred to the customer. For a portion of our business, when we process customer owned material, control is deemed to transfer to the customer as the processing is being completed. Our revenues are adjusted for variable consideration, which includes customer volume rebates and prompt payment discounts. We measure variable consideration by estimating expected outcomes using analysis and inputs based upon anticipated performance, historical data, and current and forecasted information. Customer returns are recorded as a reduction to sales on an actual basis throughout the year and also include an estimate at the end of each reporting period for future customer returns related to sales recorded prior to the end of the period. The Company generally estimates customer returns based upon the time lag that historically occurs between the sale date and the return date while also factoring in any new business conditions that might impact the historical analysis such as new product introduction. Measurement of variable consideration is reviewed by management periodically and revenue is adjusted accordingly. We do not have significant financing components. Shipping and handling activities performed by us are considered activities to fulfill the sales of our products. Amounts billed for shipping and handling are included in net sales, while costs incurred for shipping and handling are included in cost of sales. In accordance with certain contractual arrangements, we receive payment from our customers in advance related to performance obligations that are to be satisfied in the future and recognize such payments as deferred revenue, primarily related to the Company's weathertightness warranties (see Note 12 — Warranty).
Fair Value Measurements	Fair Value Measurements ASC Subtopic 820-10, Fair Value Measurements and Disclosures, requires us to use valuation techniques to measure fair value that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs are prioritized as follows: Level 1: Observable inputs such as quoted prices for identical assets or liabilities in active markets. Level 2: Other inputs that are observable directly or indirectly, such as quoted prices for similar assets or liabilities or market-corroborated inputs. Level 3: Unobservable inputs for which there is little or no market data and which require us to develop our own assumptions about how market participants would price the assets or liabilities. The following is a description of the valuation methodologies used for assets and liabilities measured at fair value. There have been no changes in the methodologies used as of October 3, 2020 and December 31, 2019. Money market: Money market funds have original maturities of three months or less. The original cost of these assets approximates fair value due to their short-term maturity. Mutual funds: Mutual funds are valued at the closing price reported in the active market in which the mutual fund is traded. Assets held for sale: Assets held for sale are valued based on current market conditions, prices of similar assets in similar condition and expected proceeds from the sale of the assets, representative of Level 3 inputs. Deferred compensation plan liability: Deferred compensation plan liability is comprised of phantom investments in the deferred compensation plan and is valued at the closing price reported in the active markets in which the money market and mutual funds are traded. Interest rate swap liability: Interest rate swap liabilities are based on cash flow hedge contracts that have fixed rate structures and are measured against market-based LIBOR yield curves. These interest rate swaps were classified within Level 2 of the fair value hierarchy because they were valued using alternative pricing sources or models that utilized market observable inputs, including current and forward interest rates.
Adopted Accounting Pronouncements and Recent Accounting Pronouncements	Adopted Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This ASU requires an entity to measure all expected credit losses for financial assets, including trade receivables, held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. Entities will now incorporate forward-looking information based on expected losses to estimate credit losses. Effective January 1, 2020, the Company adopted this guidance on a modified retrospective basis, pursuant to which it recorded a $0.7 million adjustment to increase the opening balance of accumulated deficit as of January 1, 2020 for the impact of applying the new standard. The adjustment related to recording an incremental credit loss to the accounts receivable allowance for doubtful accounts at the beginning of the first period in which the accounting standard is effective. Additional credit loss disclosures are included in Note 1 — Summary of Significant Accounting Policies. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which modifies disclosure requirements for fair value measurements under FASB Accounting Standards Codification ("ASC") 820, Fair Value Measurement. Effective January 1, 2020, the Company adopted this guidance. The application of ASU 2018-13 did not have a material effect on consolidated financial statements. In August 2018, the FASB issued ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans, which removes disclosures no longer considered cost beneficial, clarifies the specific requirements of disclosures and adds disclosure requirements identified as relevant. Effective January 1, 2020, the Company adopted this guidance. The application of ASU 2018-14 did not have a material effect on consolidated financial statements. Recent Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740 and also improves consistent application of and simplifies GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The Company will be required to adopt this guidance in the annual and interim periods for our fiscal year ending December 31, 2021, with early adoption permitted. The Company is evaluating the impact of adopting this guidance. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional guidance to ease the potential burden in accounting for reference rate reform on financial reporting. The amendments in this ASU are elective, apply to all entities that have contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of rate reform, and are effective as of March 12, 2020 through December 31, 2022. The Company is evaluating the impact of electing to apply the amendments in this guidance. Additionally, there were various other accounting standards and interpretations issued that the Company has not yet been required to adopt, none of which is expected to have a material impact on the Company’s consolidated financial statements going forward.
Leases	The Company leases certain manufacturing, warehouse and distribution locations, vehicles and equipment, including fleet vehicles. Many of these leases have options to terminate prior to or extend beyond the end of the term. The exercise of the majority of lease renewal options is at the Company’s sole discretion. Some lease agreements have variable payment terms, the majority of these are real estate agreements in which future increases in rent are based on an index. Lease agreements do not contain any material residual value guarantees or material restrictive covenants. Operating lease liabilities are recognized based on the present value of the future minimum lease payments over the reasonably expected holding period at commencement date. Few of the Company’s lease contracts provide a readily determinable implicit rate. For lease contracts without a readily determinable implicit rate, an estimated incremental borrowing rate (“IBR”) is utilized, based on information available at the inception of the lease. The IBR represents an estimate of the interest rate we would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of the lease.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

9 Months Ended

Oct. 03, 2020

The accompanying unaudited consolidated financial statements for Cornerstone Building Brands, Inc. (together with its subsidiaries, unless otherwise indicated, the “Company,” “Cornerstone,” “NCI”, “we,” “us” or “our”) have been prepared in accordance with generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by generally accepted accounting principles (“GAAP”) for complete financial statements. In the opinion of management, the unaudited consolidated financial statements included herein contain all adjustments, which consist of normal recurring adjustments, necessary to fairly present the Company’s financial position, results of operations and cash flows for the periods indicated. Operating results for the period from January 1, 2020 through October 3, 2020 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2020.

Certain reclassifications have been made to the prior period disaggregated revenue amounts in the notes to the consolidated financial statements to conform to the current presentation. The net effect of these reclassifications was not material to the consolidated financial statements (see disaggregated revenue table below).

Reporting Periods

The Company’s current fiscal quarters are based on a four-four-five week calendar with periods ending on the Saturday of the last week in the quarter except that December 31st will always be the year-end date. Therefore, the financial results of certain fiscal quarters may not be comparable to prior fiscal quarters.

Accounts Receivables and Related Allowance

The Company reports accounts receivable net of the allowance for expected credit losses. Trade accounts receivable are the result of sales of metal building products, insulated metal panels, metal coating, vinyl siding, metal siding, injection molded products, vinyl windows, aluminum windows, and other products and services to customers throughout the United States and Canada and affiliated territories, including international builders who resell to end users. Sales are primarily denominated in U.S. dollars. Credit sales do not normally require a pledge of collateral; however, various types of liens may be filed to enhance the collection process and we require payment prior to shipment for certain international shipments.

The Company establishes reserves for doubtful accounts on a customer by customer basis when we believe the required payment of specific amounts owed is unlikely to occur. Bad debt provisions are included in selling, general and administrative expenses. In establishing these reserves, the Company considers changes in the financial position of a customer, availability of security, unusual macroeconomic conditions, lien rights and bond rights as well as disputes, if any, with our customers. Our allowance for doubtful accounts reflects reserves for customer receivables to reduce receivables to amounts expected to be collected. We determine past due status as of the contractual payment date. Interest on delinquent accounts receivable is included in the trade accounts receivable balance and recognized as interest income when earned and collectability is reasonably assured. Uncollectible accounts are written off when a settlement is reached for an amount that is less than the outstanding historical balance, all collection efforts have been exhausted and/or any legal action taken by the Company has concluded.

Net Sales

The Company adopted Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), as of October 29, 2018. ASU 2014-09 provides enhancements to the quality and consistency of how revenue is reported while also improving comparability in the financial statements of companies reporting using International Financial Reporting Standards and GAAP. The core principle of this update is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services.

The Company enters into contracts that pertain to products, which are accounted for as separate performance obligations and are typically one year or less in duration. The Company does not exercise significant judgment in determining the timing for the satisfaction of performance obligations or the transaction price. Revenue is measured as the amount of consideration expected to be received in exchange for our products. The Company has elected to apply the practical expedient provided for in ASU No. 2014-09 and has not disclosed information regarding remaining performance obligations that have original expected durations of one year or less. Revenue is generally recognized when the product has shipped from our facility and control has transferred to the customer. For a portion of our business, when we process customer owned material, control is deemed to transfer to the customer as the processing is being completed.

Our revenues are adjusted for variable consideration, which includes customer volume rebates and prompt payment discounts. We measure variable consideration by estimating expected outcomes using analysis and inputs based upon anticipated performance, historical data, and current and forecasted information. Customer returns are recorded as a reduction to sales on an actual basis throughout the year and also include an estimate at the end of each reporting period for future customer returns related to sales recorded prior to the end of the period. The Company generally estimates customer returns based upon the time lag that historically occurs between the sale date and the return date while also factoring in any new business conditions that might impact the historical analysis such as new product introduction. Measurement of variable consideration is reviewed by management periodically and revenue is adjusted accordingly. We do not have significant financing components.

Shipping and handling activities performed by us are considered activities to fulfill the sales of our products. Amounts billed for shipping and handling are included in net sales, while costs incurred for shipping and handling are included in cost of sales.

In accordance with certain contractual arrangements, we receive payment from our customers in advance related to performance obligations that are to be satisfied in the future and recognize such payments as deferred revenue, primarily related to the Company's weathertightness warranties (see Note 12 — Warranty).

Fair Value Measurements

ASC Subtopic 820-10, Fair Value Measurements and Disclosures, requires us to use valuation techniques to measure fair value that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs are prioritized as follows:

Level 1: Observable inputs such as quoted prices for identical assets or liabilities in active markets.

Level 2: Other inputs that are observable directly or indirectly, such as quoted prices for similar assets or liabilities or market-corroborated inputs.

Level 3: Unobservable inputs for which there is little or no market data and which require us to develop our own assumptions about how market participants would price the assets or liabilities.

The following is a description of the valuation methodologies used for assets and liabilities measured at fair value. There have been no changes in the methodologies used as of October 3, 2020 and December 31, 2019.

Money market: Money market funds have original maturities of three months or less. The original cost of these assets approximates fair value due to their short-term maturity.

Mutual funds: Mutual funds are valued at the closing price reported in the active market in which the mutual fund is traded.

Assets held for sale: Assets held for sale are valued based on current market conditions, prices of similar assets in similar condition and expected proceeds from the sale of the assets, representative of Level 3 inputs.

Deferred compensation plan liability: Deferred compensation plan liability is comprised of phantom investments in the deferred compensation plan and is valued at the closing price reported in the active markets in which the money market and mutual funds are traded.

Interest rate swap liability: Interest rate swap liabilities are based on cash flow hedge contracts that have fixed rate structures and are measured against market-based LIBOR yield curves. These interest rate swaps were classified within Level 2 of the fair value hierarchy because they were valued using alternative pricing sources or models that utilized market observable inputs, including current and forward interest rates.

Adopted Accounting Pronouncements and Recent Accounting Pronouncements

Adopted Accounting Pronouncements

In June 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This ASU requires an entity to measure all expected credit losses for financial assets, including trade receivables, held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. Entities will now incorporate forward-looking information based on expected losses to estimate credit losses. Effective January 1, 2020, the Company adopted this guidance on a modified retrospective basis, pursuant to which it recorded a $0.7 million adjustment to increase the opening balance of accumulated deficit as of January 1, 2020 for the impact of applying the new standard. The adjustment related to recording an incremental credit loss to the accounts receivable allowance for doubtful accounts at the beginning of the first period in which the accounting standard is effective. Additional credit loss disclosures are included in Note 1 — Summary of Significant Accounting Policies.

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which modifies disclosure requirements for fair value measurements under FASB Accounting Standards Codification ("ASC") 820, Fair Value Measurement. Effective January 1, 2020, the Company adopted this guidance. The application of ASU 2018-13 did not have a material effect on consolidated financial statements.

In August 2018, the FASB issued ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans, which removes disclosures no longer considered cost beneficial, clarifies the specific requirements of disclosures and adds disclosure requirements identified as relevant. Effective January 1, 2020, the Company adopted this guidance. The application of ASU 2018-14 did not have a material effect on consolidated financial statements.

Recent Accounting Pronouncements

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740 and also improves consistent application of and simplifies GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The Company will be required to adopt this guidance in the annual and interim periods for our fiscal year ending December 31, 2021, with early adoption permitted. The Company is evaluating the impact of adopting this guidance.

In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional guidance to ease the potential burden in accounting for reference rate reform on financial reporting. The amendments in this ASU are elective, apply to all entities that have contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of rate reform, and are effective as of March 12, 2020 through December 31, 2022. The Company is evaluating the impact of electing to apply the amendments in this guidance.

Additionally, there were various other accounting standards and interpretations issued that the Company has not yet been required to adopt, none of which is expected to have a material impact on the Company’s consolidated financial statements going forward.

Leases

The Company leases certain manufacturing, warehouse and distribution locations, vehicles and equipment, including fleet vehicles. Many of these leases have options to terminate prior to or extend beyond the end of the term. The exercise of the

majority of lease renewal options is at the Company’s sole discretion. Some lease agreements have variable payment terms, the majority of these are real estate agreements in which future increases in rent are based on an index. Lease agreements do not contain any material residual value guarantees or material restrictive covenants.

Operating lease liabilities are recognized based on the present value of the future minimum lease payments over the reasonably expected holding period at commencement date. Few of the Company’s lease contracts provide a readily determinable implicit rate. For lease contracts without a readily determinable implicit rate, an estimated incremental borrowing rate (“IBR”) is utilized, based on information available at the inception of the lease. The IBR represents an estimate of the interest rate we would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of the lease.