SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
Jun. 29, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements for Cornerstone Building Brands, Inc. 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, 2019 through June 29, 2019 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2019.
Reporting Periods	Reporting Periods On November 16, 2018, the Company’s Board of Directors approved a change to the Company’s fiscal year end from a 52/53 week year with the Company’s fiscal year end on the Sunday closest to October 31 to a calendar year of the twelve-month period from January 1 to December 31. The Company elected to change its fiscal year end in connection with the Merger (as defined below) to align the Company’s fiscal year end with Ply Gem’s (as defined below). As a result of this change, the Company filed a Transition Report on Form 10-Q that included the financial information for the transition period from October 29, 2018 to December 31, 2018, which period is referred to herein as the “Transition Period”. The financial statements contained herein are being filed as part of a Quarterly Report on Form 10-Q for the period from March 31, 2019 through June 29, 2019. References in this Quarterly Report on Form 10-Q to “fiscal year 2018” or “fiscal 2018” refer to the period from October 30, 2017 through October 28, 2018. The results of operations for the three and six months ended April 29, 2018 are presented herein as the comparable period to the three and six months ended June 29, 2019. The Company did not recast the consolidated financial statements for the period from March 31, 2018 to June 29, 2018 or January 1, 2018 to June 29, 2018, because the financial reporting processes in place at that time included certain procedures that were completed only on a quarterly basis. Consequently, to recast this period would have been impractical. 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.
Adopted Accounting Pronouncements and Recent Accounting Pronouncements	Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases, to increase transparency and comparability among organizations by recognizing right-of-use assets and lease liabilities on the balance sheet and disclosing key information about leasing transactions. Effective January 1, 2019, the Company adopted the guidance initially applying the standard to leases existing at, or entered into after, the January 1, 2019 adoption date. The Company has elected only the package of three transition practical expedients available under the new standard. The short-term lease recognition exemption has been elected for all leases that qualify as well as the practical expedient to not separate lease and non-lease components for all leases other than leases of durable tooling. The adoption of the new standard resulted in the recognition of additional operating liabilities of $304.1 million with corresponding right-of-use (“ROU”) assets of $304.1 million, based on the present value of the remaining minimum rental payments. The Company recognized no adjustment to opening balance of accumulated deficit as of January 1, 2019. The new standard also provides for practice expedients for an entity’s ongoing accounting. Additional disclosures on leases are included in Note 8 — Leases. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software—General (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract, which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The accounting for the service element of a hosting arrangement that is a service contract is not affected by these amendments. Effective January 1, 2019, the Company early adopted this guidance on a prospective basis. The application of ASU 2018-15 did not have a material impact on our consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) as subsequently amended. ASU 2014-09 supersedes the revenue recognition requirements in ASC Topic 605, Revenue Recognition, and most industry-specific guidance. The core principle of the guidance 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. We performed an assessment of the differences between the new revenue standard and current accounting practices. As part of our implementation process, we identified significant revenue streams and evaluated a sample of contracts within each significant revenue stream in order to determine the effect of the standard on our revenue recognition practices. We completed this evaluation and have established new policies, procedures, and internal controls in our adoption of the new revenue standard. We adopted this guidance on a modified retrospective basis, pursuant to which we recorded a $2.6 million adjustment to increase the opening balance of accumulated deficit as of October 29, 2018 (the first day of the Transition Period) for the impact of applying the new revenue standard. The adjustment related to changes in the timing of revenue recognition for our weathertightness warranties in our Commercial segment. Additional disaggregated revenue disclosures are included in Note 1 — Summary of Significant Accounting Policies. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, which provides guidance on eight cash flow classification issues with the objective of reducing differences in practice. We adopted this guidance on a retrospective basis in the Transition Period. The application of ASU 2016-15 did not have a material impact on our consolidated financial statements. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other than Inventory, which eliminates the exception that prohibits the recognition of current and deferred income tax effects for intra-entity transfers of assets other than inventory until the asset has been sold to an outside party. We adopted this guidance on a modified retrospective basis, pursuant to which we recorded a $0.7 million adjustment to increase the opening balance of accumulated deficit as of October 29, 2018 (the first day of the Transition Period) for the impact of applying the new standard. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (a consensus of the FASB Emerging Issues Task Force), which clarifies how entities should present restricted cash and restricted cash equivalents in the statement of cash flows. Entities will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. An entity with a material balance of restricted cash and restricted cash equivalents must disclose information about the nature of the restrictions. We adopted this guidance on a retrospective basis in the Transition Period. The adoption of this guidance resulted in restricted cash activity previously included in financing activities on our consolidated statement of cash flows to be included as part of the beginning and ending balances of cash and cash equivalents and restricted cash in our consolidated statements of cash flows. In March 2017, the FASB issued ASU 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, which amends the requirements related to the income statement presentation of the components of net periodic benefit cost for employer sponsored defined benefit pension and other postretirement benefit plans. Under the new guidance, an entity must disaggregate and present the service cost component of net periodic benefit cost in the same income statement line items as other employee compensation costs arising from services rendered during the period, and only the service cost component will be eligible for capitalization. Other components of net periodic benefit cost will be presented separately from the line items that include the service cost. We adopted this guidance in the Transition Period on a retrospective basis to adopt the requirement for separate presentation of the income statement service cost and other components, and on a prospective transition method to adopt the requirement to limit the capitalization of benefit cost to the service component. The adoption of ASU 2017-07 did not have a material impact on our consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting, which provides clarity on the accounting for modifications of stock-based awards. The Company adopted this guidance on a prospective basis in the Transition Period for share-based payment awards modified on or after the adoption date. The adoption of ASU 2017-09 did not have a material impact on our consolidated financial statements. In August 2017, the FASB issued ASU No. 2017-12, Targeted Improvements to Accounting for Hedging Activities. This ASU’s objectives are to (1) improve the transparency and understandability of information conveyed to financial statement users about an entity’s risk management activities by better aligning the entity’s financial reporting for hedging relationships with those risk management activities; and (2) reduce the complexity of and simplify the application of hedge accounting by preparers. ASU No. 2017-12 is effective for interim and annual reporting periods beginning after December 15, 2018. The Company adopted this guidance on a prospective basis for fiscal 2019. The adoption of ASU 2017-12 did not have a material impact on our consolidated financial statements. Recent Accounting Pronouncements In June 2016, the 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. ASU 2016-13 will be effective for our fiscal year ending December 31, 2020, including interim periods within that fiscal year. We are evaluating the impact that the adoption of this ASU will have on our consolidated financial position, result of operations and cash flows. 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 ASC 820, Fair Value Measurement. We will be required to adopt this guidance retrospectively in the annual and interim periods for our fiscal year ending December 31, 2020, with early adoption permitted. We are evaluating the impact of adopting this guidance. 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. We will be required to adopt this guidance for our fiscal year ending December 31, 2020, with early adoption permitted. Certain provisions are applied prospectively while others are applied retrospectively. We are evaluating the impact of adopting 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	Effective January 1, 2019, the Company adopted ASU 2016-02, Leases, applying the standard to leases existing at the effective date. For arrangements entered into following the transition date, applicability of the standard is determined at inception. 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 payments, 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 these contracts, an estimated incremental borrowing rate (“IBR”) is utilized, based on information available at the inception of the lease. The Company’s IBR is determined based on securing borrowings, further described in Note 13 - Long-term Debt and Note Payable.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

6 Months Ended

Jun. 29, 2019

The accompanying unaudited consolidated financial statements for Cornerstone Building Brands, Inc. 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, 2019 through June 29, 2019 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2019.

Reporting Periods

On November 16, 2018, the Company’s Board of Directors approved a change to the Company’s fiscal year end from a 52/53 week year with the Company’s fiscal year end on the Sunday closest to October 31 to a calendar year of the twelve-month period from January 1 to December 31. The Company elected to change its fiscal year end in connection with the Merger (as defined below) to align the Company’s fiscal year end with Ply Gem’s (as defined below). As a result of this change, the Company filed a Transition Report on Form 10-Q that included the financial information for the transition period from October 29, 2018 to December 31, 2018, which period is referred to herein as the “Transition Period”. The financial statements contained herein are being filed as part of a Quarterly Report on Form 10-Q for the period from March 31, 2019 through June 29, 2019. References in this Quarterly Report on Form 10-Q to “fiscal year 2018” or “fiscal 2018” refer to the period from October 30, 2017 through October 28, 2018. The results of operations for the three and six months ended April 29, 2018 are presented herein as the comparable period to the three and six months ended June 29, 2019. The Company did not recast the consolidated financial statements for the period from March 31, 2018 to June 29, 2018 or January 1, 2018 to June 29, 2018, because the financial reporting processes in place at that time included certain procedures that were completed only on a quarterly basis. Consequently, to recast this period would have been impractical.

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.

Adopted Accounting Pronouncements and Recent Accounting Pronouncements

Adopted Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02, Leases, to increase transparency and comparability among organizations by recognizing right-of-use assets and lease liabilities on the balance sheet and disclosing key information about leasing transactions. Effective January 1, 2019, the Company adopted the guidance initially applying the standard to leases existing at, or entered into after, the January 1, 2019 adoption date. The Company has elected only the package of three transition practical expedients available under the new standard. The short-term lease recognition exemption has been elected for all leases that qualify as well as the practical expedient to not separate lease and non-lease components for all leases other than leases of durable tooling.

The adoption of the new standard resulted in the recognition of additional operating liabilities of $304.1 million with corresponding right-of-use (“ROU”) assets of $304.1 million, based on the present value of the remaining minimum rental payments. The Company recognized no adjustment to opening balance of accumulated deficit as of January 1, 2019. The new standard also provides for practice expedients for an entity’s ongoing accounting. Additional disclosures on leases are included in Note 8 — Leases.

In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software—General (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract, which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The accounting for the service element of a hosting arrangement that is a service contract is not affected by these amendments. Effective January 1, 2019, the Company early adopted this guidance on a prospective basis. The application of ASU 2018-15 did not have a material impact on our consolidated financial statements.

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) as subsequently amended. ASU 2014-09 supersedes the revenue recognition requirements in ASC Topic 605, Revenue Recognition, and most industry-specific guidance. The core principle of the guidance 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. We performed an assessment of the differences between the new revenue standard and current accounting practices. As part of our implementation process, we identified significant revenue streams and evaluated a sample of contracts within each significant revenue stream in order to determine the effect of the standard on our revenue recognition practices. We completed this evaluation and have established new policies, procedures, and internal controls in our adoption of the new revenue standard. We adopted this guidance on a modified retrospective basis, pursuant to which we recorded a $2.6 million adjustment to increase the opening balance of accumulated deficit as of October 29, 2018 (the first day of the Transition Period) for the impact of applying the new revenue standard. The adjustment related to changes in the timing of revenue recognition for our weathertightness warranties in our Commercial segment. Additional disaggregated revenue disclosures are included in Note 1 — Summary of Significant Accounting Policies.

In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, which provides guidance on eight cash flow classification issues with the objective of reducing differences in practice. We adopted this guidance on a retrospective basis in the Transition Period. The application of ASU 2016-15 did not have a material impact on our consolidated financial statements.

In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other than Inventory, which eliminates the exception that prohibits the recognition of current and deferred income tax effects for intra-entity transfers of assets other than inventory until the asset has been sold to an outside party. We adopted this guidance on a modified retrospective basis, pursuant to which we recorded a $0.7 million adjustment to increase the opening balance of accumulated deficit as of October 29, 2018 (the first day of the Transition Period) for the impact of applying the new standard.

In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (a consensus of the FASB Emerging Issues Task Force), which clarifies how entities should present restricted cash and restricted cash equivalents in the statement of cash flows. Entities will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. An entity with a material balance of restricted cash and restricted cash equivalents must disclose information about the nature of the restrictions. We adopted this guidance on a retrospective basis in the Transition Period. The adoption of this guidance resulted in restricted cash activity previously included in financing activities on our consolidated statement of cash flows to be included as part of the beginning and ending balances of cash and cash equivalents and restricted cash in our consolidated statements of cash flows.

In March 2017, the FASB issued ASU 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, which amends the requirements related to the income statement presentation of the components of net periodic benefit cost for employer sponsored defined benefit pension and other postretirement benefit plans. Under the new guidance, an entity must disaggregate and present the service cost component of net periodic benefit cost in the same income statement line items as other employee compensation costs arising from services rendered during the period, and only the service cost component will be eligible for capitalization. Other components of net periodic benefit cost will be presented separately from the line items that include the service cost. We adopted this guidance in the Transition Period on a retrospective basis to adopt the requirement for separate presentation of the income statement service cost and other components, and on a prospective transition method to adopt the requirement to limit the capitalization of benefit cost to the service component. The adoption of ASU 2017-07 did not have a material impact on our consolidated financial statements.

In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting, which provides clarity on the accounting for modifications of stock-based awards. The Company adopted this guidance on a prospective basis in the Transition Period for share-based payment awards modified on or after the adoption date. The adoption of ASU 2017-09 did not have a material impact on our consolidated financial statements.

In August 2017, the FASB issued ASU No. 2017-12, Targeted Improvements to Accounting for Hedging Activities. This ASU’s objectives are to (1) improve the transparency and understandability of information conveyed to financial statement users about an entity’s risk management activities by better aligning the entity’s financial reporting for hedging relationships with those risk management activities; and (2) reduce the complexity of and simplify the application of hedge accounting by preparers. ASU No. 2017-12 is effective for interim and annual reporting periods beginning after December 15, 2018. The Company adopted this guidance on a prospective basis for fiscal 2019. The adoption of ASU 2017-12 did not have a material impact on our consolidated financial statements.

Recent Accounting Pronouncements

In June 2016, the 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. ASU 2016-13 will be effective for our fiscal year ending December 31, 2020, including interim periods within that fiscal year. We are evaluating the impact that the adoption of this ASU will have on our consolidated financial position, result of operations and cash flows.

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 ASC 820, Fair Value Measurement. We will be required to adopt this guidance retrospectively in the annual and interim periods for our fiscal year ending December 31, 2020, with early adoption permitted. We are evaluating the impact of adopting this guidance.

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. We will be required to adopt this guidance for our fiscal year ending December 31, 2020, with early adoption permitted. Certain provisions are applied prospectively while others are applied retrospectively. We are evaluating the impact of adopting 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

Effective January 1, 2019, the Company adopted ASU 2016-02, Leases, applying the standard to leases existing at the effective date. For arrangements entered into following the transition date, applicability of the standard is determined at inception.

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 payments, 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 these contracts, an estimated incremental borrowing rate (“IBR”) is utilized, based on information available at the inception of the lease. The Company’s IBR is determined based on securing borrowings, further described in Note 13 - Long-term Debt and Note Payable.