Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
Mar. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation—The Condensed and Consolidated Financial Statements include the accounts of the Company and its wholly owned subsidiaries and have been prepared in United States dollars ("USD") in accordance with generally accepted accounting principles in the United States of America ("GAAP"). The Condensed and Consolidated Financial Statements included herein are unaudited, but in the opinion of management, such financial statements include all adjustments, consisting of normal recurring adjustments, necessary to summarize fairly the Company's financial position, results of operations, and cash flows for the interim periods presented. The interim results reported in these Condensed and Consolidated Financial Statements should not be taken as indicative of results that may be expected for the entire year. For a more comprehensive understanding of ADT and its Condensed and Consolidated Financial Statements, please review these interim financial statements in conjunction with the Company's audited financial statements included in its Annual Report on Form 10-K for the fiscal year ended September 25, 2015 ("2015 Form 10-K"), which was filed with the SEC on November 12, 2015. Historically, the Company had a 52- or 53-week fiscal year that ended on the last Friday in September. Fiscal year 2015 was a 52-week fiscal year. On October 14, 2015, the Company's Board of Directors approved a change to the Company's fiscal year end from the last Friday in September to September 30 of each year, and thereafter the end of each fiscal quarter will be the last day of the calendar month end. The fiscal year change is effective for the 2016 fiscal year, which began on September 26, 2015, the day after the last day of the 2015 fiscal year, and will end on September 30, 2016. This change better aligns the Company's external reporting with the monthly recurring nature of revenues and expenses associated with its customer base. The Company conducts business through its operating entities. During the fourth quarter of fiscal year 2015, the Company changed its segment reporting structure in connection with a change in the manner in which the Chief Executive Officer, who is the chief operating decision maker ("CODM"), evaluates performance and makes decisions about how to allocate resources. This change resulted in the reorganization of the Company's single operating segment into two operating segments, United States and Canada. These operating segments are also the Company's reportable segments and are identified by the Company based on how resources are allocated and operating decisions are made. Where applicable, presentation of the Company's operating segments and prior period amounts reported herein are based on the new segment structure. Refer to Note 9 for segment data. All intercompany transactions have been eliminated. The results of companies acquired are included in the Condensed and Consolidated Financial Statements from the effective date of acquisition.
Inventories	Inventories—Inventories are recorded at the lower of cost (average cost) or market value.
Financial Instruments	Financial Instruments—The Company's financial instruments consist primarily of cash and cash equivalents, accounts receivable, accounts payable, debt, and derivative financial instruments. Due to their short-term nature, the fair value of cash and cash equivalents, accounts receivable, and accounts payable approximated carrying value as of March 31, 2016 and September 25, 2015. Long-Term Debt Instruments—The fair value of the Company's unsecured notes was determined using broker-quoted market prices, which are considered Level 2 inputs. The carrying amount of debt outstanding under the Company's revolving credit facility approximates fair value as interest rates on these borrowings approximate current market rates, which are considered Level 2 inputs.
Derivatives Instruments	Derivative Instruments—All derivative financial instruments are reported on the Condensed and Consolidated Balance Sheets at fair value. For derivative financial instruments designated as fair value hedges, the changes in fair value of both the derivatives and the hedged items are recognized in the Condensed and Consolidated Statements of Operations.
Recent Accounting Pronouncements	Recent Accounting Pronouncements—In May 2014, the Financial Accounting Standards Board ("FASB") issued authoritative guidance which sets forth a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. Companies may use either a full retrospective or a modified retrospective approach to adopt this guidance. In August 2015, the FASB issued an amendment to defer the effective date of this guidance by one year to December 15, 2017, for annual reporting periods, including interim reporting periods within those periods, beginning after that date. Early adoption is permitted, but not before the original effective date of December 15, 2016. This guidance, including all subsequently issued amendments by the FASB to this guidance, will be effective for the Company in the first quarter of fiscal year 2019. The Company is currently evaluating the impact of this guidance. In April 2015, the FASB issued authoritative guidance to simplify the presentation of debt issuance costs and require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. The recognition and measurement guidance for debt issuance costs are not affected by the amendments in this guidance. This guidance is to be applied on a retrospective basis and is effective for financial statements issued for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015. This guidance will be effective for the Company in the first quarter of fiscal year 2017. Early adoption is permitted for financial statements that have not been previously issued. The adoption of this guidance is not expected to have a material impact on the Company's financial position, results of operations, or cash flows. In April 2015, the FASB issued authoritative guidance regarding the accounting for fees paid in a cloud computing arrangement. The new standard provides guidance to customers about whether a cloud computing arrangement includes a software license. If a cloud computing arrangement includes a software license, then the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015. This guidance will be effective for the Company in the first quarter of fiscal year 2017. Early adoption is permitted. Companies may elect to adopt this guidance using either (1) a prospective approach for all arrangements entered into or materially modified after the effective date, or (2) a retrospective approach. The Company is currently evaluating the impact of this guidance. In July 2015, the FASB issued authoritative guidance to simplify the subsequent measurement of inventory. Under this new standard, an entity should measure inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2016, and will be effective for the Company in the first quarter of fiscal year 2018. The amendments in this guidance should be applied prospectively with earlier application permitted as of the beginning of an interim or annual reporting period. The Company is currently evaluating the impact of this guidance. In November 2015, the FASB issued authoritative guidance to simplify the presentation of deferred income taxes, and require that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. The current requirement that deferred tax liabilities and assets be offset and presented as a single amount for each jurisdiction is not affected by the amendments in this guidance. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2016, and will be effective for the Company in the first quarter of fiscal year 2018. The amendments in this guidance may be applied either prospectively to all deferred tax liabilities and assets or retrospectively to all periods presented. Early adoption is permitted as of the beginning of an interim or annual reporting period. The Company is currently evaluating the impact of this guidance. In January 2016, the FASB issued authoritative guidance related to the accounting for equity investments, financial liabilities under the fair value option, and the presentation and disclosure requirements for financial instruments. In addition, this update clarifies the guidance related to the valuation allowance assessment when recognizing deferred tax assets resulting from the unrealized losses on available-for-sale debt securities. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017, and will be effective for the Company in the first quarter of fiscal year 2019. Entities may early adopt the provision within this guidance to record fair value changes for financial liabilities under the fair value option resulting from instrument-specific credit risk in other comprehensive income. An entity should apply the amendments in the standard by means of a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption. The amendments in the standard that address equity securities without readily determinable fair values should be applied prospectively to equity investments that exist as of the date of adoption of the standard. The Company is currently evaluating the impact of this guidance. In February 2016, the FASB issued authoritative guidance on accounting for leases. This new guidance requires lessees to recognize a right-to-use asset and a lease liability for substantially all leases and to disclose key information about leasing arrangements. The recognition, measurement, and presentation of expenses and cash flows for lessees will remain significantly unchanged from current guidance. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018, and will be effective for the Company in the first quarter of fiscal year 2020. Early adoption is permitted. The guidance is to be adopted using a modified retrospective approach as of the earliest period presented. The Company is currently evaluating the impact of this guidance. In March 2016, the FASB issued authoritative guidance to simplify the accounting for employee share-based payment transactions. The new guidance simplifies the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as simplifies the classification of transactions related to share-based payments in the statement of cash flows. The guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods, and will be effective for the Company in the first quarter of fiscal year 2018. Early adoption is permitted, provided that all amendments are adopted in the same period. The guidance also includes the acceptable or required transition methods for each of the various amendments included in the new standard. The Company is currently evaluating the impact of this guidance.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)

6 Months Ended

Mar. 31, 2016

Basis of Presentation—The Condensed and Consolidated Financial Statements include the accounts of the Company and its wholly owned subsidiaries and have been prepared in United States dollars ("USD") in accordance with generally accepted accounting principles in the United States of America ("GAAP"). The Condensed and Consolidated Financial Statements included herein are unaudited, but in the opinion of management, such financial statements include all adjustments, consisting of normal recurring adjustments, necessary to summarize fairly the Company's financial position, results of operations, and cash flows for the interim periods presented. The interim results reported in these Condensed and Consolidated Financial Statements should not be taken as indicative of results that may be expected for the entire year. For a more comprehensive understanding of ADT and its Condensed and Consolidated Financial Statements, please review these interim financial statements in conjunction with the Company's audited financial statements included in its Annual Report on Form 10-K for the fiscal year ended September 25, 2015 ("2015 Form 10-K"), which was filed with the SEC on November 12, 2015.

Historically, the Company had a 52- or 53-week fiscal year that ended on the last Friday in September. Fiscal year 2015 was a 52-week fiscal year. On October 14, 2015, the Company's Board of Directors approved a change to the Company's fiscal year end from the last Friday in September to September 30 of each year, and thereafter the end of each fiscal quarter will be the last day of the calendar month end. The fiscal year change is effective for the 2016 fiscal year, which began on September 26, 2015, the day after the last day of the 2015 fiscal year, and will end on September 30, 2016. This change better aligns the Company's external reporting with the monthly recurring nature of revenues and expenses associated with its customer base.

The Company conducts business through its operating entities. During the fourth quarter of fiscal year 2015, the Company changed its segment reporting structure in connection with a change in the manner in which the Chief Executive Officer, who is the chief operating decision maker ("CODM"), evaluates performance and makes decisions about how to allocate resources. This change resulted in the reorganization of the Company's single operating segment into two operating segments, United States and Canada. These operating segments are also the Company's reportable segments and are identified by the Company based on how resources are allocated and operating decisions are made. Where applicable, presentation of the Company's operating segments and prior period amounts reported herein are based on the new segment structure. Refer to Note 9 for segment data.

All intercompany transactions have been eliminated. The results of companies acquired are included in the Condensed and Consolidated Financial Statements from the effective date of acquisition.

Inventories

Inventories—Inventories are recorded at the lower of cost (average cost) or market value.

Financial Instruments

Financial Instruments—The Company's financial instruments consist primarily of cash and cash equivalents, accounts receivable, accounts payable, debt, and derivative financial instruments. Due to their short-term nature, the fair value of cash and cash equivalents, accounts receivable, and accounts payable approximated carrying value as of March 31, 2016 and September 25, 2015.

Long-Term Debt Instruments—The fair value of the Company's unsecured notes was determined using broker-quoted market prices, which are considered Level 2 inputs. The carrying amount of debt outstanding under the Company's revolving credit facility approximates fair value as interest rates on these borrowings approximate current market rates, which are considered Level 2 inputs.

Derivatives Instruments

Derivative Instruments—All derivative financial instruments are reported on the Condensed and Consolidated Balance Sheets at fair value. For derivative financial instruments designated as fair value hedges, the changes in fair value of both the derivatives and the hedged items are recognized in the Condensed and Consolidated Statements of Operations.

Recent Accounting Pronouncements

Recent Accounting Pronouncements—In May 2014, the Financial Accounting Standards Board ("FASB") issued authoritative guidance which sets forth a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. Companies may use either a full retrospective or a modified retrospective approach to adopt this guidance. In August 2015, the FASB issued an amendment to defer the effective date of this guidance by one year to December 15, 2017, for annual reporting periods, including interim reporting periods within those periods, beginning after that date. Early adoption is permitted, but not before the original effective date of December 15, 2016. This guidance, including all subsequently issued amendments by the FASB to this guidance, will be effective for the Company in the first quarter of fiscal year 2019. The Company is currently evaluating the impact of this guidance.

In April 2015, the FASB issued authoritative guidance to simplify the presentation of debt issuance costs and require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. The recognition and measurement guidance for debt issuance costs are not affected by the amendments in this guidance. This guidance is to be applied on a retrospective basis and is effective for financial statements issued for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015. This guidance will be effective for the Company in the first quarter of fiscal year 2017. Early adoption is permitted for financial statements that have not been previously issued. The adoption of this guidance is not expected to have a material impact on the Company's financial position, results of operations, or cash flows.

In April 2015, the FASB issued authoritative guidance regarding the accounting for fees paid in a cloud computing arrangement. The new standard provides guidance to customers about whether a cloud computing arrangement includes a software license. If a cloud computing arrangement includes a software license, then the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015. This guidance will be effective for the Company in the first quarter of fiscal year 2017. Early adoption is permitted. Companies may elect to adopt this guidance using either (1) a prospective approach for all arrangements entered into or materially modified after the effective date, or (2) a retrospective approach. The Company is currently evaluating the impact of this guidance.

In July 2015, the FASB issued authoritative guidance to simplify the subsequent measurement of inventory. Under this new standard, an entity should measure inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2016, and will be effective for the Company in the first quarter of fiscal year 2018. The amendments in this guidance should be applied prospectively with earlier application permitted as of the beginning of an interim or annual reporting period. The Company is currently evaluating the impact of this guidance.

In November 2015, the FASB issued authoritative guidance to simplify the presentation of deferred income taxes, and require that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. The current requirement that deferred tax liabilities and assets be offset and presented as a single amount for each jurisdiction is not affected by the amendments in this guidance. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2016, and will be effective for the Company in the first quarter of fiscal year 2018. The amendments in this guidance may be applied either prospectively to all deferred tax liabilities and assets or retrospectively to all periods presented. Early adoption is permitted as of the beginning of an interim or annual reporting period. The Company is currently evaluating the impact of this guidance.

In January 2016, the FASB issued authoritative guidance related to the accounting for equity investments, financial liabilities under the fair value option, and the presentation and disclosure requirements for financial instruments. In addition, this update clarifies the guidance related to the valuation allowance assessment when recognizing deferred tax assets resulting from the unrealized losses on available-for-sale debt securities. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017, and will be effective for the Company in the first quarter of fiscal year 2019. Entities may early adopt the provision within this guidance to record fair value changes for financial liabilities under the fair value option resulting from instrument-specific credit risk in other comprehensive income. An entity should apply the amendments in the standard by means of a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption. The amendments in the standard that address equity securities without readily determinable fair values should be applied prospectively to equity investments that exist as of the date of adoption of the standard. The Company is currently evaluating the impact of this guidance.

In February 2016, the FASB issued authoritative guidance on accounting for leases. This new guidance requires lessees to recognize a right-to-use asset and a lease liability for substantially all leases and to disclose key information about leasing arrangements. The recognition, measurement, and presentation of expenses and cash flows for lessees will remain significantly unchanged from current guidance. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018, and will be effective for the Company in the first quarter of fiscal year 2020. Early adoption is permitted. The guidance is to be adopted using a modified retrospective approach as of the earliest period presented. The Company is currently evaluating the impact of this guidance.

In March 2016, the FASB issued authoritative guidance to simplify the accounting for employee share-based payment transactions. The new guidance simplifies the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as simplifies the classification of transactions related to share-based payments in the statement of cash flows. The guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods, and will be effective for the Company in the first quarter of fiscal year 2018. Early adoption is permitted, provided that all amendments are adopted in the same period. The guidance also includes the acceptable or required transition methods for each of the various amendments included in the new standard. The Company is currently evaluating the impact of this guidance.