Summary of Significant Accounting Policies	3 Months Ended
Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying financial statements present the consolidated financial position, results of operations, and cash flows of AmerisourceBergen Corporation and its subsidiaries, including less than wholly-owned subsidiaries in which AmerisourceBergen Corporation has a controlling financial interest (the "Company"), as of the dates and for the periods indicated. All intercompany accounts and transactions have been eliminated in consolidation. The accompanying unaudited consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles ("GAAP") for interim financial information, the instructions to Form 10-Q, and Rule 10-01 of Regulation S-X. In the opinion of management, all adjustments (consisting only of normal recurring accruals, except as otherwise disclosed herein) considered necessary to present fairly the financial position as of December 31, 2018 and the results of operations and cash flows for the interim periods ended December 31, 2018 and 2017 have been included. Certain information and footnote disclosures normally included in financial statements presented in accordance with U.S. GAAP, but which are not required for interim reporting purposes, have been omitted. The accompanying unaudited consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended September 30, 2018. The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect amounts reported in the financial statements and accompanying notes. Actual amounts could differ from these estimated amounts. Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU No. 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASU 2014-09"). ASU 2014-09 supersedes the revenue recognition requirements in Accounting Standards Codification ("ASC") 605 - "Revenue Recognition" and most industry-specific guidance throughout the Codification. ASU 2014-09 outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. The standard's core principle is that a company 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. ASU 2014-09 was originally scheduled to be effective for annual reporting periods beginning after December 15, 2016, including interim periods within those reporting periods. In July 2015, the FASB deferred the effective date of ASU 2014-09 by one year. In March 2016, the FASB issued ASU No. 2016-08, "Revenue from Contracts with Customers (Topic 606) - Principal versus Agent Considerations" ("ASU 2016-08"), which clarifies the implementation guidance for principal versus agent considerations in ASU 2014-09. In April 2016, the FASB issued ASU No. 2016-10, "Revenue from Contracts with Customers (Topic 606) - Identifying Performance Obligations and Licensing" ("ASU 2016-10"), which amends the guidance in ASU 2014-09 related to identifying performance obligations and accounting for licenses of intellectual property. The Company must adopt ASU 2016-08 and ASU 2016-10 with ASU 2014-09, collectively ASC 606. The Company adopted ASC 606 as of October 1, 2018 on a modified retrospective basis for all open contracts as of October 1, 2018. The adoption had an immaterial impact on the Company’s October 1, 2018 retained earnings and will not have a material impact on the Company's revenues, results of operations, or cash flows. The Company did not record any material contract assets, contract liabilities, or deferred contract costs in its Consolidated Balance Sheet upon adoption. The Company's revenues are primarily generated from the distribution of pharmaceutical products. The Company also generates revenues from global commercialization services, which include clinical trial support, post-approval and commercialization support, and global specialty transportation and logistics for the biopharmaceutical industry. See Note 13 for the Company's disaggregated revenue. The Company recognizes revenue related to the distribution of products at a point in time when title and control transfers to customers and there is no further obligation to provide services related to such products. Service revenue is recognized over the period that services are provided to the customer. The Company is generally the principal in a transaction; therefore, revenue is primarily recorded on a gross basis. When the Company is the principal in a transaction, it has determined that it controls the ability to direct the use of the product or service prior to transfer to a customer, it is primarily responsible for fulfilling the promise to provide the product or service to its customer, it has discretion in establishing pricing, and it controls the relationship with the customer. Revenue is recognized at the amount of consideration expected to be received, which is generally based on a purchase order, and is net of estimated sales returns and allowances, other customer incentives, and sales tax. The Company’s customer sales return policy generally allows customers to return products only if the products can be resold at full value or returned to suppliers for full credit. The Company records an accrual for estimated customer sales returns at the time of sale to the customer based upon historical return trends. As of December 31, 2018 and September 30, 2018, the Company’s accrual for estimated customer sales returns was $973.8 million and $988.8 million, respectively. As of December 31, 2018, due to the adoption of ASC 606, the Company records an asset for the right to recover products from its customers in Right to Recover Asset on its Consolidated Balance Sheet. The Company's asset for the right to recover products from its customers was in Merchandise Inventories on its Consolidated Balance Sheet as of September 30, 2018 and for all prior periods. The Company elected the practical expedient to expense costs to obtain a contract when incurred when the amortization period would have been one year or less. Additionally, the Company elected the practical expedients to not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less, (ii) contracts for which the Company recognizes revenue at the amount to which it has the right to invoice for services performed, and (iii) for contracts for which the variable consideration is allocated entirely to a wholly unsatisfied performance obligation or to a wholly unsatisfied promise to transfer a distinct good or service that forms part of a single performance obligation. Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)" ("ASU 2016-02"). ASU 2016-02 aims to increase transparency and comparability across organizations by requiring lease assets and lease liabilities to be recognized on the balance sheet as well as key information to be disclosed regarding lease arrangements. ASU 2016-02 is effective for annual reporting periods beginning after December 15, 2018 and interim periods within those fiscal years. Entities are permitted to adopt the standard early, and a modified retrospective application is required. The Company anticipates that the adoption of this new accounting standard will have a material impact on the Company's Consolidated Balance Sheets. However, the Company is continues to evaluate the impact of adopting this new accounting standard, and, therefore, cannot reasonably estimate the impact on the results of operations or cash flows at this time. The Company has begun the process of implementing the adoption of this standard, including the implementation of new policies, processes, and controls.The Company will adopt this standard in the first quarter of fiscal 2020. As of December 31, 2018, there were no other recently-issued accounting standards that may have a material impact on the Company’s financial position, results of operations, or cash flows upon their adoption.

Summary of Significant Accounting Policies

Basis of Presentation

The accompanying financial statements present the consolidated financial position, results of operations, and cash flows of AmerisourceBergen Corporation and its subsidiaries, including less than wholly-owned subsidiaries in which AmerisourceBergen Corporation has a controlling financial interest (the "Company"), as of the dates and for the periods indicated. All intercompany accounts and transactions have been eliminated in consolidation.

The accompanying unaudited consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles ("GAAP") for interim financial information, the instructions to Form 10-Q, and Rule 10-01 of Regulation S-X. In the opinion of management, all adjustments (consisting only of normal recurring accruals, except as otherwise disclosed herein) considered necessary to present fairly the financial position as of December 31, 2018 and the results of operations and cash flows for the interim periods ended December 31, 2018 and 2017 have been included. Certain information and footnote disclosures normally included in financial statements presented in accordance with U.S. GAAP, but which are not required for interim reporting purposes, have been omitted. The accompanying unaudited consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended September 30, 2018.

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect amounts reported in the financial statements and accompanying notes. Actual amounts could differ from these estimated amounts.

Recently Adopted Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU No. 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASU 2014-09"). ASU 2014-09 supersedes the revenue recognition requirements in Accounting Standards Codification ("ASC") 605 - "Revenue Recognition" and most industry-specific guidance throughout the Codification. ASU 2014-09 outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. The standard's core principle is that a company 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. ASU 2014-09 was originally scheduled to be effective for annual reporting periods beginning after December 15, 2016, including interim periods within those reporting periods. In July 2015, the FASB deferred the effective date of ASU 2014-09 by one year.

In March 2016, the FASB issued ASU No. 2016-08, "Revenue from Contracts with Customers (Topic 606) - Principal versus Agent Considerations" ("ASU 2016-08"), which clarifies the implementation guidance for principal versus agent considerations in ASU 2014-09. In April 2016, the FASB issued ASU No. 2016-10, "Revenue from Contracts with Customers (Topic 606) - Identifying Performance Obligations and Licensing" ("ASU 2016-10"), which amends the guidance in ASU 2014-09 related to identifying performance obligations and accounting for licenses of intellectual property. The Company must adopt ASU 2016-08 and ASU 2016-10 with ASU 2014-09, collectively ASC 606.

The Company adopted ASC 606 as of October 1, 2018 on a modified retrospective basis for all open contracts as of October 1, 2018. The adoption had an immaterial impact on the Company’s October 1, 2018 retained earnings and will not have a material impact on the Company's revenues, results of operations, or cash flows. The Company did not record any material contract assets, contract liabilities, or deferred contract costs in its Consolidated Balance Sheet upon adoption.

The Company's revenues are primarily generated from the distribution of pharmaceutical products. The Company also generates revenues from global commercialization services, which include clinical trial support, post-approval and commercialization support, and global specialty transportation and logistics for the biopharmaceutical industry. See Note 13 for the Company's disaggregated revenue.

The Company recognizes revenue related to the distribution of products at a point in time when title and control transfers to customers and there is no further obligation to provide services related to such products. Service revenue is recognized over the period that services are provided to the customer. The Company is generally the principal in a transaction; therefore, revenue is primarily recorded on a gross basis. When the Company is the principal in a transaction, it has determined that it controls the ability to direct the use of the product or service prior to transfer to a customer, it is primarily responsible for fulfilling the promise to provide the product or service to its customer, it has discretion in establishing pricing, and it controls the relationship with the customer. Revenue is recognized at the amount of consideration expected to be received, which is generally based on a purchase order, and is net of estimated sales returns and allowances, other customer incentives, and sales tax.

The Company’s customer sales return policy generally allows customers to return products only if the products can be resold at full value or returned to suppliers for full credit. The Company records an accrual for estimated customer sales returns at the time of sale to the customer based upon historical return trends. As of December 31, 2018 and September 30, 2018, the Company’s accrual for estimated customer sales returns was $973.8 million and $988.8 million, respectively. As of December 31, 2018, due to the adoption of ASC 606, the Company records an asset for the right to recover products from its customers in Right to Recover Asset on its Consolidated Balance Sheet. The Company's asset for the right to recover products from its customers was in Merchandise Inventories on its Consolidated Balance Sheet as of September 30, 2018 and for all prior periods.

The Company elected the practical expedient to expense costs to obtain a contract when incurred when the amortization period would have been one year or less. Additionally, the Company elected the practical expedients to not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less, (ii) contracts for which the Company recognizes revenue at the amount to which it has the right to invoice for services performed, and (iii) for contracts for which the variable consideration is allocated entirely to a wholly unsatisfied performance obligation or to a wholly unsatisfied promise to transfer a distinct good or service that forms part of a single performance obligation.

Recently Issued Accounting Pronouncements Not Yet Adopted

In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)" ("ASU 2016-02"). ASU 2016-02 aims to increase transparency and comparability across organizations by requiring lease assets and lease liabilities to be recognized on the balance sheet as well as key information to be disclosed regarding lease arrangements. ASU 2016-02 is effective for annual reporting periods beginning after December 15, 2018 and interim periods within those fiscal years. Entities are permitted to adopt the standard early, and a modified retrospective application is required. The Company anticipates that the adoption of this new accounting standard will have a material impact on the Company's Consolidated Balance Sheets. However, the Company is continues to evaluate the impact of adopting this new accounting standard, and, therefore, cannot reasonably estimate the impact on the results of operations or cash flows at this time. The Company has begun the process of implementing the adoption of this standard, including the implementation of new policies, processes, and controls.The Company will adopt this standard in the first quarter of fiscal 2020.

As of December 31, 2018, there were no other recently-issued accounting standards that may have a material impact on the Company’s financial position, results of operations, or cash flows upon their adoption.