Cencora (COR) 10-K 20 Nov 18 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2018	Oct. 31, 2018	Mar. 31, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	AMERISOURCEBERGEN CORP
Entity Central Index Key	1,140,859
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		211,933,493
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 11,568,943,708
Trading Symbol	abc
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Current assets:
Cash and cash equivalents	$ 2,492,516	$ 2,435,115
Accounts receivable, less allowances for returns and doubtful accounts: 2018 — $1,036,333; 2017 — $1,050,361	11,314,226	10,303,324
Merchandise inventories	11,918,508	11,461,428
Prepaid expenses and other	169,122	103,432
Total current assets	25,894,372	24,303,299
Property and equipment, at cost:
Land	39,875	40,302
Buildings and improvements	1,086,909	979,589
Machinery, equipment, and other	2,281,124	2,071,314
Total property and equipment	3,407,908	3,091,205
Less accumulated depreciation	(1,515,484)	(1,293,260)
Property and equipment, net	1,892,424	1,797,945
Goodwill	6,664,272	6,044,281
Other intangible assets	2,947,828	2,833,281
Other assets	270,942	337,664
TOTAL ASSETS	37,669,838	35,316,470
Current liabilities:
Accounts payable	26,836,873	25,404,042
Accrued expenses and other	881,157	1,402,002
Short-term debt	151,657	12,121
Total current liabilities	27,869,687	26,818,165
Long-term debt	4,158,532	3,429,934
Long-term financing obligation	352,296	351,635
Accrued income taxes	299,600	84,257
Deferred income taxes	1,829,410	2,492,612
Other liabilities	110,352	75,406
Stockholders' equity:
Common stock, $0.01 par value — authorized, issued, and outstanding: 2018 — 600,000,000 shares, 283,588,463 shares and 213,217,882 shares; 2017 — 600,000,000 shares, 280,584,076 shares and 217,993,598 shares	2,836	2,806
Additional paid-in capital	4,715,473	4,517,635
Retained earnings	3,720,582	2,395,218
Accumulated other comprehensive loss	(79,253)	(95,850)
Treasury stock, at cost: 2018 — 70,370,581 shares; 2017 — 62,590,478 shares	(5,426,814)	(4,755,348)
Total AmerisourceBergen Corporation stockholders' equity	2,932,824	2,064,461
Noncontrolling interest	117,137	0
Total equity	3,049,961	2,064,461
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 37,669,838	$ 35,316,470

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Current assets:
Allowances for returns and doubtful accounts	$ 1,036,333	$ 1,050,361
Stockholders' equity:
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, authorized (shares)	600,000,000	600,000,000
Common stock, issued (shares)	283,588,463	280,584,076
Common stock, outstanding (shares)	213,217,882	217,993,598
Treasury stock (shares)	70,370,581	62,590,478

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenue	$ 167,939,635,000	$ 153,143,826,000	$ 146,849,686,000
Cost of goods sold	163,327,318,000	148,597,824,000	142,577,080,000
Gross profit	4,612,317,000	4,546,002,000	4,272,606,000
Operating expenses:
Distribution, selling, and administrative	2,460,301,000	2,128,730,000	2,091,237,000
Depreciation	283,971,000	237,100,000	212,242,000
Amortization	181,156,000	160,503,000	152,493,000
Warrants	0	0	140,342,000
Employee severance, litigation, and other	183,520,000	959,327,000	102,911,000
Pension settlement	0	0	47,607,000
Goodwill impairment	59,684,000	0	0
Operating income	1,443,685,000	1,060,342,000	1,525,774,000
Other loss (income)	25,469,000	(2,730,000)	(5,048,000)
Interest expense, net	174,699,000	145,185,000	139,912,000
Loss on consolidation of equity investments	42,328,000	0	0
Loss on early retirement of debt	23,766,000	0	0
Income before income taxes	1,177,423,000	917,887,000	1,390,910,000
Income tax (benefit) expense	(438,469,000)	553,403,000	(37,019,000)
Net income	1,615,892,000	364,484,000	1,427,929,000
Net loss attributable to noncontrolling interest	(42,513,000)	0	0
Net income attributable to AmerisourceBergen Corporation	$ 1,658,405,000	$ 364,484,000	$ 1,427,929,000
Earnings per share:
Basic (usd per share)	$ 7.61	$ 1.67	$ 6.73
Diluted (usd per share)	$ 7.53	$ 1.64	$ 6.32
Weighted average common shares outstanding:
Basic (shares)	217,872	218,375	212,206
Diluted (shares)	220,336	221,602	225,959

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 1,615,892	$ 364,484	$ 1,427,929
Other comprehensive income:
Foreign currency translation adjustments	(36,904)	16,540	(9,311)
Loss on consolidation of equity investments	45,941	0	0
Pension plan adjustment, net of tax of $19,054	0	0	31,538
Other	(756)	1,918	(202)
Total other comprehensive income	8,281	18,458	22,025
Total comprehensive income	1,624,173	382,942	1,449,954
Comprehensive loss attributable to noncontrolling interest	50,829	0	0
Comprehensive income attributable to AmerisourceBergen Corporation	$ 1,675,002	$ 382,942	$ 1,449,954

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) $ in Thousands	12 Months Ended
	Sep. 30, 2016USD ($)
Statement of Comprehensive Income [Abstract]
Pension plan adjustment, tax	$ 19,054

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury [Member]	Noncontrolling Interest [Member]
Balance, beginning of period at Sep. 30, 2015	$ 616,386	$ 2,750	$ 3,736,477	$ 1,164,489	$ (136,333)	$ (4,150,997)	$ 0
Increase (decrease) in stockholders' equity
Net income (loss)	1,427,929			1,427,929
Other comprehensive income (loss)	22,025				22,025
Cash dividends	(288,477)			(288,477)
Exercises of stock options	74,768	22	74,746
Share-based compensation expense	64,992		64,992
Common stock purchases for employee stock purchase plan	(548)		(548)
Warrants expense	140,342		140,342
Exercises of warrants	2,360,479		336,998			2,023,481
Purchases of common stock	(1,866,344)					(1,866,344)
Settlement of accelerated share repurchase transaction	(400,000)		(20,000)			(380,000)
Employee tax withholdings related to restricted share vesting	(22,148)					(22,148)
Other	0	6	(6)
Balance, end of period at Sep. 30, 2016	2,129,404	2,778	4,333,001	2,303,941	(114,308)	(4,396,008)	0
Increase (decrease) in stockholders' equity
Adoption of ASU 2016-09	47,063			47,063
Net income (loss)	364,484			364,484
Other comprehensive income (loss)	18,458				18,458
Cash dividends	(320,270)			(320,270)
Exercises of stock options	102,923	25	102,898
Share-based compensation expense	62,206		62,206
Common stock purchases for employee stock purchase plan	(467)		(467)
Purchases of common stock	(329,929)					(329,929)
Settlement of accelerated share repurchase transaction	0		20,000			(20,000)
Employee tax withholdings related to restricted share vesting	(9,411)					(9,411)
Other	0	3	(3)
Balance, end of period at Sep. 30, 2017	2,064,461	2,806	4,517,635	2,395,218	(95,850)	(4,755,348)	0
Increase (decrease) in stockholders' equity
Consolidation of variable interest entity	167,966						167,966
Net income (loss)	1,615,892			1,658,405			(42,513)
Other comprehensive income (loss)	8,281				16,597		(8,316)
Cash dividends	(333,041)			(333,041)
Exercises of stock options	138,456	27	138,429
Share-based compensation expense	62,316		62,316
Common stock purchases for employee stock purchase plan	(341)		(341)
Purchases of common stock	(663,220)					(663,220)
Employee tax withholdings related to restricted share vesting	(8,246)					(8,246)
Other	(2,563)	3	(2,566)
Balance, end of period at Sep. 30, 2018	$ 3,049,961	$ 2,836	$ 4,715,473	$ 3,720,582	$ (79,253)	$ (5,426,814)	$ 117,137

CONSOLIDATED STATEMENTS OF CH_2

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement of Stockholders' Equity [Abstract]
Cash dividends (usd per share)	$ 1.52	$ 1.46	$ 1.36

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOW - USD ($)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
OPERATING ACTIVITIES
Net income	$ 1,615,892,000	$ 364,484,000	$ 1,427,929,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, including amounts charged to cost of goods sold	318,483,000	262,420,000	232,538,000
Amortization, including amounts charged to interest expense	191,626,000	169,911,000	159,628,000
Provision for doubtful accounts	16,660,000	8,934,000	13,124,000
(Benefit) provision for deferred income taxes	(795,524,000)	319,069,000	(130,927,000)
Warrants expense	0	0	140,342,000
Share-based compensation expense	62,316,000	62,206,000	64,992,000
LIFO expense (credit)	67,324,000	(157,782,000)	200,230,000
Goodwill impairment	59,684,000	0	0
Impairment of non-customer note receivable	30,000,000	0	0
Loss on consolidation of equity investments	42,328,000	0	0
Loss on early retirement of debt	23,766,000	0	0
(Gain) loss on the sale of assets	(6,444,000)	1,314,000	2,234,000
Gain on sale of business	0	(3,677,000)	0
Pension settlement	0	0	47,607,000
Other	(12,634,000)	10,107,000	(7,405,000)
Changes in operating assets and liabilities, excluding the effects of acquisitions and divestitures:
Accounts receivable	(657,770,000)	(1,277,896,000)	(912,724,000)
Merchandise inventories	(4,923,000)	(431,454,000)	(1,107,252,000)
Prepaid expenses and other assets	(57,211,000)	33,646,000	(46,159,000)
Accounts payable	859,036,000	1,473,389,000	3,011,508,000
Income taxes payable	209,899,000	27,192,000	93,043,000
Accrued expenses	(537,905,000)	661,174,000	(43,267,000)
Other liabilities	(13,215,000)	(18,899,000)	33,056,000
NET CASH PROVIDED BY OPERATING ACTIVITIES	1,411,388,000	1,504,138,000	3,178,497,000
INVESTING ACTIVITIES
Capital expenditures	(336,411,000)	(466,397,000)	(464,616,000)
Cost of acquired companies, net of cash acquired	(785,299,000)	(61,648,000)	(2,731,356,000)
Cost of equity investments	0	(11,347,000)	(19,034,000)
Proceeds from sale of business	0	12,094,000	0
Proceeds from sales of investment securities available-for-sale	0	74,778,000	101,829,000
Purchases of investment securities available-for-sale	0	(48,635,000)	(42,083,000)
Other	10,596,000	3,114,000	(13,919,000)
NET CASH USED IN INVESTING ACTIVITIES	(1,111,114,000)	(498,041,000)	(3,169,179,000)
FINANCING ACTIVITIES
Senior notes and other loan borrowings	1,314,430,000	0	1,000,000,000
Senior notes and other loan repayments	(681,001,000)	(750,000,000)	(800,000,000)
Borrowings under revolving and securitization credit facilities	25,129,704,000	9,336,400,000	8,846,876,000
Repayments under revolving and securitization credit facilities	(25,127,438,000)	(9,335,953,000)	(8,333,662,000)
Payment of premium on early retirement of debt	(22,348,000)	0	0
Purchases of common stock	(639,235,000)	(329,929,000)	(2,266,344,000)
Exercises of warrants	0	0	2,360,479,000
Exercises of stock options	138,456,000	102,923,000	74,768,000
Cash dividends on common stock	(333,041,000)	(320,270,000)	(288,477,000)
Employee tax withholdings related to restricted share vesting	(8,246,000)	(9,411,000)	(22,148,000)
Other	(14,154,000)	(6,574,000)	(6,420,000)
NET CASH (USED IN) PROVIDED BY FINANCING ACTIVITIES	(242,873,000)	(1,312,814,000)	565,072,000
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	57,401,000	(306,717,000)	574,390,000
Cash and cash equivalents at beginning of year	2,435,115,000	2,741,832,000	2,167,442,000
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 2,492,516,000	$ 2,435,115,000	$ 2,741,832,000

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies AmerisourceBergean Corporation and its subsidiaries, including less than wholly-owned subsidiaries in which AmerisourceBergen Corporation has a controlling financial interest (the "Company"), is one of the largest global pharmaceutical sourcing and distribution services companies, helping both healthcare providers and pharmaceutical and biotech manufacturers improve patient access to products and enhance patient care. The Company delivers innovative programs and services designed to increase the effectiveness and efficiency of the pharmaceutical supply chain in both human and animal health. Basis of Presentation The accompanying financial statements present the consolidated financial position, results of operations, and cash flows of the Company as of the dates and for the periods indicated. All intercompany accounts and transactions have been eliminated in consolidation. The preparation of financial statements in conformity with U.S. generally accepted accounting principles ("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 due to uncertainties inherent in such estimates. Management periodically evaluates estimates used in the preparation of the financial statements for continued reasonableness. Certain reclassifications have been made to prior-period amounts in order to conform to the current year presentation. Recently Adopted Accounting Pronouncements In March 2016, the FASB issued ASU No. 2016-09, "Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting" ("ASU 2016-09"). ASU 2016-09 requires all income tax effects of awards to be recognized in the income statement when the awards vest or are exercised. It also allows an employer to repurchase more of an employee's shares for tax withholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur. ASU 2016-09 was effective for annual reporting periods beginning after December 15, 2016 and interim periods within those fiscal years. During the quarter ended December 31, 2016, the Company early adopted ASU 2016-09, which resulted in a cumulative adjustment to retained earnings and the establishment of a deferred tax asset as of October 1, 2016 of $47.1 million for previously unrecognized tax benefits. The Company elected to adopt the Statement of Cash Flows presentation of the excess tax benefits prospectively. 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 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. The Company completed its evaluation of the impact of adopting ASU 2016-08, ASU 2016-10, and ASU 2014-09, collectively Accounting Standards Codification 606 or "ASC 606". The Company adopted ASC 606 as of October 1, 2018 on a modified retrospective basis. 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. 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 continues to evaluate the impact of adopting this new accounting guidance and, therefore, cannot reasonably estimate the impact on the results of operations or cash flows at this time. The Company expects to adopt this standard in the first quarter of fiscal 2020. As of September 30, 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. Business Combinations The assets acquired and liabilities assumed from the acquired business are recorded at fair value, with the residual of the purchase price recorded as goodwill. The results of operations of the acquired businesses are included in the Company's operating results from the dates of acquisition. Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less to be cash equivalents. The carrying value of cash equivalents approximates fair value. Concentrations of Credit Risk and Allowance for Doubtful Accounts The Company sells its merchandise inventories to a large number of customers in the healthcare industry that include institutional and retail healthcare providers. Institutional healthcare providers include acute care hospitals, health systems, mail order pharmacies, long-term care and other alternate care pharmacies and providers of pharmacy services to such facilities, and physician offices. Retail healthcare providers include national and regional retail drugstore chains, independent community pharmacies, pharmacy departments of supermarkets and mass merchandisers, and veterinarians. The financial condition of the Company's customers can be affected by changes in government reimbursement policies as well as by other economic pressures in the healthcare industry. The Company's trade accounts receivables are exposed to credit risk. Revenue from the various agreements and arrangements with the Company's largest customer in the fiscal year ended September 30, 2018 , Walgreens Boots Alliance, Inc. ("WBA"), accounted for approximately 33% of revenue and represented approximately 49% of accounts receivable, net of incentives, as of September 30, 2018 . Express Scripts, Inc., the Company's second largest customer in the fiscal year ended September 30, 2018 , accounted for approximately 13% of revenue and represented approximately 8% of accounts receivable, net as of September 30, 2018 . The Company generally does not require collateral for trade receivables. In determining the appropriate allowance for doubtful accounts, the Company considers a combination of factors, such as the aging of trade receivables, industry trends, and its customers' financial strength, credit standing, and payment and default history. Changes in these factors, among others, may lead to adjustments in the Company's allowance for doubtful accounts. The calculation of the required allowance requires judgment by Company management as to the impact of those and other factors on the ultimate realization of its trade receivables. Each of the Company's business units performs ongoing credit evaluations of its customers' financial condition and maintains reserves for probable bad debt losses based upon historical experience and for specific credit problems when they arise. There were no significant changes to this process during the fiscal years ended September 30, 2018 , 2017 , and 2016 , and bad debt expense was computed in a consistent manner during these periods. The Company maintains cash and cash equivalents with several financial institutions. Deposits held with banks may exceed the amount of insurance provided on such deposits. These deposits may be redeemed upon demand and are maintained with financial institutions with reputable credit and, therefore, bear minimal credit risk. The Company seeks to mitigate such risks by monitoring the risk profiles of these counterparties. The Company also seeks to mitigate risk by monitoring the investment strategy of money market accounts in which it is invested, which are classified as cash equivalents. Contingencies Loss Contingencies: In the ordinary course of its business, the Company becomes involved in lawsuits, administrative proceedings, government subpoenas, government investigations, and other disputes, including antitrust, commercial, environmental, product liability, intellectual property, regulatory, employment discrimination, and other matters. Significant damages or penalties may be sought from the Company in some matters, and some matters may require years for the Company to resolve. The Company records a liability when it is probable that a loss has been incurred and the amount is reasonably estimable. The Company also performs an assessment of the materiality of loss contingencies where a loss is either not probable or it is reasonably possible that a loss could be incurred in excess of amounts accrued. If a loss or an additional loss has at least a reasonable possibility of occurring and the impact on the financial statements would be material, the Company provides disclosure of the loss contingency in the notes to its financial statements. The Company reviews all contingencies at least quarterly to determine whether the likelihood of loss has changed and to assess whether a reasonable estimate of the loss or the range of the loss can be made (see Note 13 ). Gain Contingencies: The Company records gain contingencies when they are realized. Gains from antitrust litigation settlements are realized upon the receipt of cash and recorded as a reduction to cost of goods sold because they represent a recovery of amounts historically paid to manufacturers to originally acquire the pharmaceuticals that were the subject of the antitrust litigation settlements (see Note 14 ). Derivative Financial Instruments The Company records all derivative financial instruments on the balance sheet at fair value and complies with established criteria for designation and effectiveness of hedging relationships. The Company's policy prohibits it from entering into derivative financial instruments for speculative or trading purposes. The Company has one foreign currency denominated contract outstanding that hedges the foreign currency exchange risk of a C$17.5 million note outstanding as of September 30, 2018 . Foreign Currency When the functional currency of the Company's foreign operations is the applicable local currency, assets and liabilities are translated into U.S. dollars using the current exchange rates in effect at the balance sheet date, while revenues and expenses are translated at the weighted average exchange rates for the period. The resulting translation adjustments are recorded as a component of Accumulated Other Comprehensive Loss within Stockholders' Equity. Goodwill and Other Intangible Assets Goodwill and other intangible assets with indefinite lives, such as certain trademarks and trade names, are not amortized; rather, they are tested for impairment at least annually. For the purpose of these impairment tests, we can elect to perform a qualitative assessment to determine if it is more likely than not that the fair values of its reporting units and indefinite-lived intangible assets are less than the respective carrying values of those reporting units and indefinite-lived intangible assets, respectively. The Company elected to bypass performing the qualitative assessment and, in the fourth quarter of fiscal 2018, went directly to performing our annual quantitative assessments of the goodwill and indefinite-lived intangible assets for the current year. The Company may elect to perform the qualitative annual assessment in future periods. The goodwill impairment test requires us to compare the carrying value of the reporting unit's net assets to the fair value of the reporting unit. If the fair value exceeds the carrying value, no further evaluation is required, and no impairment loss is recognized. If the carrying amount exceeds the fair value, the difference between the carrying value and the fair value is recorded as an impairment loss, the amount of which may not exceed the total amount of goodwill allocated to the reporting unit. Goodwill arises from acquisitions or consolidations of specific operating companies and is assigned to the reporting unit in which a particular operating company resides. The Company identifies its reporting units based upon the Company's management reporting structure, beginning with its operating segments. The Company evaluates whether the components within its operating segments have similar economic characteristics, which include the nature of the components' products, services, and production processes, the types of customers and the methods by which products or services are delivered to customers, and the components' regulatory environment. The Company's reporting units include Pharmaceutical Distribution Services, Profarma Distribuidora de Produtos Farmacêuticos S.A. ("Profarma"), AmerisourceBergen Consulting Services ("ABCS"), World Courier, and MWI Animal Health ("MWI"). The Company utilizes an income-based approach to value its reporting units, with the exception of the Profarma reporting unit, the fair value of which is based upon its publicly-traded stock price, plus an estimated control premium. The income-based approach relies on a discounted cash flow analysis, which considers forecasted cash flows discounted at an appropriate discount rate, to determine the fair value of each reporting unit. The Company generally believes that market participants would use a discounted cash flow analysis to determine the fair value of the Company's reporting units in a sale transaction. The annual goodwill impairment test requires the Company to make a number of assumptions and estimates concerning future levels of revenue growth, operating margins, depreciation, amortization, capital expenditures, and working capital requirements, which are based upon the Company's long-range plan. The discount rate is an estimate of the overall after-tax rate of return required by a market participant whose weighted average cost of capital includes both debt and equity, including a risk premium. While the Company uses the best available information to prepare its cash flows and discount rate assumptions, actual future cash flows and/or market conditions could differ significantly resulting in future impairment charges related to recorded goodwill balances. While there are always changes in assumptions to reflect changing business and market conditions, the Company's overall methodology and the population of assumptions used have remained unchanged. The impairment test for indefinite-lived intangibles other than goodwill (certain trademarks and trade names) consists of a comparison of the fair value of the indefinite-lived intangible asset to the carrying value of the asset as of the impairment testing date. The Company estimates the fair value of its indefinite-lived intangibles using the relief from royalty method. The Company believes the relief from royalty method is a widely used valuation technique for such assets. The fair value derived from the relief from royalty method is measured as the discounted cash flow savings realized from owning such indefinite-lived trademarks and trade names and not having to pay a royalty for their use. The Company completed its required annual impairment tests relating to goodwill and indefinite-lived intangible assets in the fourth quarter of the fiscal years ended September 30, 2018 , 2017 , and 2016 . The Company recorded a goodwill impairment of $59.7 million in its Profarma reporting unit in connection with its fiscal 2018 annual impairment test (see Note 5). No goodwill impairments were recorded in the fiscal years ended September 30, 2017 and 2016. No indefinite-lived intangible asset impairments were recorded in the fiscal years ended September 30, 2018, 2017, and 2016. In connection with the goodwill impairment recorded in the Profarma reporting unit, the Company first performed a recoverability assessment of Profarma's long-lived assets by comparing its undiscounted cash flows to the carrying value of the asset group, and it was determined to be recoverable; however, the forecasted undiscounted cash flows used to perform the recoverability assessment are inherently uncertain and include assumptions that could differ from actual results in future periods. Finite-lived intangible assets are amortized using the straight-line method over the estimated useful lives of the assets. The Company performs a recoverability assessment of its long-lived assets when impairment indicators are present. PharMEDium Healthcare Holdings, Inc.'s ("PharMEDium") long-lived assets were also tested for recoverability in fiscal 2018 due to the existence of an impairment indicator. The Company voluntarily suspended production activities in December 2017 at its largest compounding facility located in Memphis, Tennessee after U.S. Food and Drug Administration ("FDA") inspections of PharMEDium's compounding facilities. The Company concluded that the suspension of production activity represented an impairment indicator of PharMEDium's long-lived assets and, therefore, performed a recoverability assessment of PharMEDium's long-lived assets. The recoverability assessment was based on the carrying value of the PharMEDium asset group, excluding goodwill. The carrying value of the asset group was $903 million as of September 30, 2018. The Company concluded that PharMEDium's long-lived assets are recoverable as of September 30, 2018; however, the forecasted undiscounted cash flows used to perform the recoverability assessment are inherently uncertain and include assumptions, such as the timing of resumed production activities and profitability, that could differ from actual results in future periods. Income Taxes The Company accounts for income taxes using a method that requires recognition of deferred tax assets and liabilities for expected future tax consequences of temporary differences that currently exist between tax bases and financial reporting bases of the Company's assets and liabilities (commonly known as the asset and liability method). In assessing the need to establish a valuation allowance on deferred tax assets, the Company considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained upon examination by the taxing authorities, including resolutions of any related appeals or litigation processes, based upon the technical merits of the position. Tax benefits associated with uncertain tax positions that have met the recognition criteria are measured and recorded based upon the highest probable outcome that is more than 50% likely to be realized after full disclosure and resolution of a tax examination. Investment Securities Available-For-Sale The Company's marketable debt securities have been classified and accounted for as available-for-sale. Management determines the appropriate classification of its investments at the time of purchase and evaluates the classifications at each balance sheet date. The Company classifies its marketable debt securities as either short-term or long-term based upon each instrument's underlying contractual maturity date. Marketable debt securities with maturities of 12 months or less are classified as short-term and marketable debt securities with maturities greater than 12 months are classified as long-term. The Company's marketable debt securities are carried at fair value, with unrealized gains and losses reported as a component of Accumulated Other Comprehensive Loss in Stockholders' Equity, with the exception of unrealized losses believed to be other-than-temporary, which are reported in earnings in the current period. The cost of securities sold is based upon the specific identification method. As of September 30, 2018 and 2017 , the Company had no investment securities available-for-sale. Investments The Company first evaluates its investments in accordance with the variable interest model to determine whether it has a controlling financial interest in an investment. This evaluation is made as of the date on which the Company makes its initial investment, and subsequent evaluations are made if the structure of the investment changes. If it has determined that an investment is a variable interest entity ("VIE"), the Company evaluates whether the VIE is required to be consolidated. When the Company holds rights that give it the power to direct the activities of an entity that most significantly impact the entity's economic performance, combined with the obligation to absorb an entity's losses and the right to receive benefits, the Company consolidates a VIE. If it is determined that an investment is not a VIE, the Company then evaluates its investments under the voting interest model and generally consolidates investments in which it holds an ownership interest of greater than 50%. When the Company consolidates less than wholly-owned subsidiaries, it discloses its noncontrolling interest in its consolidated financial statements. The Company uses the equity method of accounting for its investments in entities in which it has significant influence; generally, this represents an ownership interest of between 20% and 50%. A decline in value that is determined to be other-than-temporary is recorded as an impairment charge as a component of earnings in the period in which that determination is made. Leases The Company is often involved in the construction of its distribution facilities. In certain cases, the Company makes payments for certain structural components included in the lessor's construction of the leased assets, which result in the Company being deemed the owner of the leased assets for accounting purposes. As a result, regardless of the significance of the payments, Accounting Standards Codification 840, Leases, ("ASC 840") defines those payments as automatic indicators of ownership and requires the Company to capitalize the lessor's total project cost with a corresponding financing obligation. Upon completion of the lessor's project, the Company performs a sale-leaseback analysis pursuant to ASC 840 to determine if these assets and the related financing obligations can be derecognized from the Company's Consolidated Balance Sheet. If the Company is deemed to have "continuing involvement," the leased assets and the related financing obligations remain on the Company's Consolidated Balance Sheet and are amortized over the life of the assets and the lease term, respectively. All other leases are considered operating leases in accordance with ASC 840. Assets subject to an operating lease and the related lease payments are not recorded on the Company's Consolidated Balance Sheet. Rent expense is recognized on a straight-line basis over the expected lease term and is recorded in Distribution, Selling, and Administrative in the Company's Consolidated Statements of Operations. Manufacturer Incentives The Company considers fees and other incentives received from its suppliers relating to the purchase or distribution of inventory to represent product discounts, and, as a result, they are recognized within cost of goods sold upon the sale of the related inventory. Merchandise Inventories Inventories are stated at the lower of cost or market. Cost for approximately 75% and 80% of the Company's inventories as of September 30, 2018 and 2017 , respectively, has been determined using the last-in, first-out ("LIFO") method. If the Company had used the first-in, first-out method of inventory valuation, which approximates current replacement cost, inventories would have been approximately $1,534.4 million and $1,467.0 million higher than the amounts reported as of September 30, 2018 and 2017 , respectively. The Company recorded LIFO expense of $67.3 million and $200.2 million in the fiscal years ended September 30, 2018 and 2016, respectively, and a LIFO credit of $157.8 million in the fiscal year ended September 30, 2017 . The annual LIFO provision is affected by changes in inventory quantities, product mix, and manufacturer pricing practices, which may be impacted by market and other external influences, many of which are difficult to predict. Changes to any of the above factors can have a material impact to the Company's annual LIFO provision. Property and Equipment Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, which range from 3 to 40 years for buildings and improvements and from 3 to 10 years for machinery, equipment, and other. The costs of repairs and maintenance are charged to expense as incurred. The Company capitalizes project costs relating to computer software developed or obtained for internal use when the activities related to the project reach the application development stage. Costs that are associated with preliminary stage activities, training, maintenance, and all other post-implementation stage activities are expensed as they are incurred. Software development costs are depreciated using the straight-line method over the estimated useful lives, which range from 3 to 10 years. Revenue Recognition The Company recognizes revenue when persuasive evidence of an arrangement exists, products have been delivered or services have been rendered, the price is fixed or determinable, and collectability is reasonably assured. Revenue, as reflected in the accompanying Consolidated Statements of Operations, is net of estimated sales returns and allowances, and other customer incentives. 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. As of September 30, 2018 and 2017 , the Company's accrual for estimated customer sales returns was $988.8 million and $1,001.7 million , respectively. The Company reports the gross dollar amount of bulk deliveries to customer warehouses in revenue and the related costs in cost of goods sold. Bulk delivery transactions are arranged by the Company at the express direction of the customer, and involve either drop shipments from the supplier directly to customers' warehouse sites or cross-dock shipments from the supplier to the Company for immediate shipment to the customers' warehouse sites. The Company is a principal to these transactions because it is the primary obligor and has the ultimate and contractual responsibility for fulfillment and acceptability of the products purchased, and it bears full risk of delivery and loss for products, whether the products are drop-shipped or shipped via cross-dock. The Company also bears full credit risk associated with the creditworthiness of any bulk delivery customer. As a result, the Company records bulk deliveries to customer warehouses as gross revenues. Gross profit earned by the Company on bulk deliveries was not material in any year presented. Share-Based Compensation The Company accounts for the compensation cost of all share-based payments at fair value. The Company estimates the fair value of option grants using a binomial option pricing model. The fair value of restricted stock units and performance stock units is based upon the grant date market price of the Company’s common stock. Share-based compensation expense is recognized over the requisite service period within Distribution, Selling, and Administrative in the Consolidated Statements of Operations to correspond with the same line item as the cash compensation paid to employees. Compensation expense associated with nonvested performance stock units is dependent upon the Company's periodic assessment of the probability of the targets being achieved and its estimate of the number of shares that will ultimately be issued. The income tax effects of awards is recognized when the awards vest or are settled and are recognized in Income Tax Expense in the Company’s Consolidated Statements of Operations and in cash flows from operations in the Consolidated Statements of Cash Flows. Prior to fiscal 2017, tax benefits from share-based compensation were recorded as adjustments to Additional Paid-in Capital within Stockholders’ Equity and as cash flows from financing activities within the Statement of Cash Flows (see Recently Adopted Accounting Pronouncements). Shipping and Handling Costs Shipping and handling costs include all costs to warehouse, pick, pack, and deliver inventory to customers. These costs, which were $590.8 million , $517.3 million , and $494.7 million for the fiscal years ended September 30, 2018 , 2017 , and 2016 , respectively, are included in Distribution, Selling, and Administrative in the Company's Consolidated Statements of Operations. Supplier Reserves The Company establishes reserves against amounts due from its suppliers relating to various price and rebate incentives, including deductions or billings taken against payments otherwise due to them from the Company. These reserve estimates are established based upon the judgment of Company management after carefully considering the status of current outstanding claims, historical experience with the suppliers, the specific incentive programs, and any other pertinent information available to the Company. The Company evaluates the amounts due from its suppliers on a continual basis and adjusts the reserve estimates when appropriate based upon changes in factual circumstances. The ultimate outcome of any outstanding claim may be different than the Company's estimate. Warrants The Company accounted for the warrants issued to subsidiaries of WBA (collectively, the "Warrants") in accordance with the guidance for equity-based payments to non-employees. Using a binomial lattice model approach, the fair value of the Warrants was initially measured at the date of issuance, and the related expenses were recognized over the vesting period as an operating expense. The fair value of the Warrants was remeasured at the end of each reporting period, and an adjustment was recorded in the statement of operations to record the impact as if the newly measured fair value of the awards had been used in recognizing expense starting when the awards were originally issued and through the remeasurement date. In the fiscal year ended September 30, 2016, the Warrants were exercised by WBA in full (see Note 7 ).

Acquisitions and Investments

Acquisitions and Investments	12 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Acquisitions and Investments	Acquisitions and Investments PharMEDium On November 6, 2015, the Company acquired PharMEDium for $2.7 billion in cash, which included certain purchase price adjustments. PharMEDium is a leading national provider of outsourced compounded sterile preparations to acute care hospitals in the United States. PharMEDium's operating results are included within the Pharmaceutical Distribution Services reportable segment. The purchase price was allocated to the underlying assets acquired and liabilities assumed based upon their fair values on the date of the acquisition. The purchase price exceeded the fair value of the net tangible and intangible assets acquired by $1.8 billion , which was allocated to goodwill. The fair value of accounts receivable, inventory, and accounts payable acquired was $63.2 million , $43.1 million , and $22.8 million , respectively. The fair value of the intangible assets acquired of $1.1 billion consisted of customer relationships of $882.7 million , trade name of $167.6 million , and software technology of $52.6 million . The Company established a deferred tax liability of $356.1 million primarily in connection with the intangible assets acquired. The Company is amortizing the fair values of the acquired customer relationships and trade name over their estimated useful lives of 15 years . The fair value of the acquired software technology is being amortized over its estimated useful life of 10 years . Goodwill and intangible assets resulting from the acquisition are not deductible for income tax purposes. NEVSCO In December 2017, the Company acquired Northeast Veterinary Supply Company ("NEVSCO") for $70.0 million in cash, subject to a final working capital adjustment. NEVSCO was an independent, regional distributor of veterinary pharmaceuticals and medical supplies serving primarily the northeast region of the United States and is expected to strengthen MWI's support of independent veterinary practices and provide even greater value and care to current and future animal health customers. NEVSCO has been included within the MWI operating segment. The purchase price has been preliminarily allocated to the underlying assets acquired and liabilities assumed based upon their estimated fair values on the date of acquisition. The preliminary allocation is pending the finalization of the appraisals of intangible assets and the finalization of working capital and income tax account balances. There can be no assurance that the estimated amounts recorded will represent the final fair values. The purchase price currently exceeds the estimated fair value of the net tangible and intangible assets acquired by $30.9 million , which has been allocated to goodwill. The estimated fair value of accounts receivable, inventory, and accounts payable and accrued expenses acquired was $10.3 million , $6.7 million , and $3.0 million , respectively. The estimated fair value of the intangible assets acquired of $29.8 million primarily consists of customer relationships, which the Company is amortizing over its estimated useful life of 15 years . Goodwill and intangible assets resulting from the acquisition are expected to be deductible for income tax purposes. H.D. Smith In January 2018, the Company acquired H.D. Smith Holding Company ("H.D. Smith") for $815.0 million , subject to a final working capital adjustment. The Company funded the acquisition through the issuance of new long-term debt (see Note 6 ). H.D. Smith was the largest independent pharmaceutical wholesaler in the United States and provides full-line distribution of brand, generic, and specialty drugs, as well as high-value services and solutions for manufacturers and healthcare providers. H.D. Smith's customers include retail pharmacies, specialty pharmacies, long-term care facilities, institutional/hospital systems, and independent physicians and clinics. The acquisition strengthens the Company's core business, expands and enhances its strategic scale in pharmaceutical distribution, and expands the Company's support for independent community pharmacies. H.D. Smith has been included within the Pharmaceutical Distribution reportable segment. The purchase price has been preliminarily allocated to the underlying assets acquired and liabilities assumed based upon their estimated fair values on the date of acquisition. The preliminary allocation is incomplete principally due to the finalization of income tax account balances. There can be no assurance that the estimated amounts recorded will represent the final fair values. The purchase price currently exceeds the estimated fair value of the net tangible and intangible assets acquired by $499.9 million , which was allocated to goodwill. The fair value of accounts receivable, inventory, and accounts payable and accrued expenses acquired was $163.1 million , $350.7 million , and $366.1 million , respectively. The estimated fair value of the intangible assets acquired of $167.8 million consisted of customer relationships of $156.6 million and a tradename of $11.2 million . The Company is amortizing the estimated fair value of the customer relationships and the tradename over their estimated useful lives of 12 and 2 years, respectively. The Company established a deferred tax liability of $60.6 million primarily in connection with the intangible assets acquired. Goodwill and intangible assets resulting from the acquisition are not expected to be deductible for income tax purposes. Profarma and Specialty Joint Venture As of September 30, 2017, the Company held a noncontrolling ownership interest in Profarma, a leading pharmaceutical wholesaler in Brazil, and an ownership interest in a joint venture with Profarma to provide specialty distribution and services in the Brazilian marketplace (the "specialty joint venture"). The Company had accounted for these interests as equity method investments, which were reported in Other Assets on the Company's Consolidated Balance Sheets. In January 2018, the Company invested an additional $62.5 million in Profarma and an additional $15.6 million in the specialty joint venture to increase its ownership interests to 38.2% and 64.5% , respectively. In connection with the additional investment in Profarma, the Company received substantial governance rights, thereby requiring it to begin consolidating the operating results of Profarma as of March 31, 2018 (see Note 3 ). The Company also began to consolidate the operating results of the specialty joint venture as of March 31, 2018 due to its majority ownership interest. In September 2018, the Company made an additional investment of $23.6 million in the specialty joint venture to increase its ownership interest to 89.9% . Profarma and the specialty joint venture have been included within the Pharmaceutical Distribution reportable segment and Other, respectively. The fair value of Profarma, including the noncontrolling interest, was determined based upon an agreed-upon stock price and has been preliminarily allocated to the underlying assets and liabilities consolidated based upon their fair values at the time of the January 2018 investment. The preliminary allocation is pending the finalization of the appraisals of intangible assets and the finalization of working capital and income tax account balances. There can be no assurance that the estimated amounts recorded will represent the final fair values. The fair value of Profarma upon obtaining control exceeded the estimated fair value of the net tangible and intangible assets consolidated by $142.0 million , which was allocated to goodwill. The estimated fair value of accounts receivable, inventory, accounts payable and accrued expenses was $160.1 million , $190.5 million , and $167.7 million , respectively. The Company consolidated short-term debt and long-term debt of $209.9 million and $12.4 million , respectively, cash of $150.8 million , and recorded a noncontrolling interest of $168.0 million . The estimated fair value of the intangible assets consolidated of $84.6 million consisted of customer relationships of $25.9 million and tradenames of $58.7 million . The Company is amortizing the customer relationships over its estimated useful life of 15 years and the tradenames over their estimated useful lives of between 15 and 25 years. The Company established a deferred tax liability of $50.1 million primarily in connection with the intangible assets that were recognized. Goodwill and intangible assets resulting from the consolidation are not expected to be deductible for income tax purposes. The fair value of the specialty joint venture was determined based upon the cost of the incremental ownership percentage acquired from the January 2018 investment and was allocated to the underlying assets and liabilities consolidated based upon their estimated fair values at the time of the January 2018 investment. The preliminary allocation is pending the finalization of the appraisals of intangible assets and the finalization of working capital and income tax account balances. There can be no assurance that the estimated amounts recorded will represent the final fair values. The fair value of the specialty joint venture currently exceeds the estimated fair value of the net tangible and intangible assets consolidated by $3.5 million , which was allocated to goodwill. The estimated fair value of accounts receivable, inventory, accounts payable and accrued expenses was $65.0 million , $29.1 million , and $54.3 million , respectively. The Company consolidated short-term debt and cash of $32.7 million and $28.9 million , respectively. The estimated fair value of the intangible assets consolidated of $4.6 million is being amortized over its estimated useful life of 15 years. Goodwill and intangible assets resulting from the consolidation are not expected to be deductible for income tax purposes. In connection with the incremental Brazil investments, the Company adjusted the carrying values of its previously held equity interests in Profarma and the specialty joint venture to equal their fair values, which were determined to be $103.1 million and $31.2 million , respectively. These represent Level 2 nonrecurring fair value measurements. The adjustments resulted in a pretax loss of $42.3 million and were comprised of foreign currency translation adjustments from Accumulated Other Comprehensive Loss of $45.9 million , a $12.4 million gain on the remeasurement of Profarma's previously held equity interest, and an $8.8 million loss on the remeasurement of the specialty joint venture's previously held equity interest.

Variable Interest Entity

Variable Interest Entity	12 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entity	Variable Interest Entity As discussed in Note 2 , the Company made an additional investment in Profarma. In connection with this investment, the Company obtained substantial governance rights, allowing it to direct the activities that significantly impact Profarma’s economic performance. As such, the Company consolidated the operating results of Profarma in its consolidated financial statements as of and for the periods ended September 30, 2018 . The Company is not obligated to provide future financial support to Profarma. The following assets and liabilities of Profarma are included in the Company's Consolidated Balance Sheet: (in thousands) September 30, Cash and cash equivalents $ 26,801 Accounts receivables, net 144,646 Merchandise inventories 168,931 Prepaid expenses and other 61,924 Property and equipment, net 32,667 Goodwill 82,309 Other intangible assets 80,974 Other long-term assets 8,912 Total assets $ 607,164 Accounts payable $ 150,102 Accrued expenses and other 37,195 Short-term debt 115,461 Long-term debt 39,704 Deferred income taxes 46,137 Other long-term liabilities 31,988 Total liabilities $ 420,587 Profarma's assets can only be used to settle its obligations, and its creditors do not have recourse to the general credit of the Company.

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following illustrates domestic and foreign income before income taxes for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Domestic $ 704,935 $ 394,721 $ 906,415 Foreign 472,488 523,166 484,495 Total $ 1,177,423 $ 917,887 $ 1,390,910 The income tax (benefit) provision for the periods indicated is as follows: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Current provision: Federal $ 247,755 $ 141,071 $ 11,892 State and local 39,328 35,950 26,741 Foreign 69,972 57,313 55,275 Total current provision 357,055 234,334 93,908 Deferred (benefit) provision: Federal (828,023 ) 265,074 (119,218 ) State and local 33,887 54,995 (11,490 ) Foreign (1,388 ) (1,000 ) (219 ) Total deferred (benefit) provision (795,524 ) 319,069 (130,927 ) (Benefit) provision for income taxes $ (438,469 ) $ 553,403 $ (37,019 ) A reconciliation of the statutory U.S. federal income tax rate to the effective income tax rate for the periods indicated is as follows: Fiscal Year Ended September 30, 2018 2017 2016 Statutory U.S. federal income tax rate 24.5% 35.0% 35.0% State and local income tax rate, net of federal tax benefit (0.1) 5.4 0.6 Foreign (6.2) (14.6) (8.4) Warrants — — (32.8) Valuation allowance (1.4) 2.2 2.2 Excess tax benefits related to share-based compensation (1.8) (3.8) — Litigation settlements and accruals (see Note 13) (6.3) 34.3 — Goodwill impairment (see Note 5) 1.7 — — Tax reform (52.0) — — Capital gain on distribution 3.6 — — Other 0.8 1.8 0.7 Effective income tax rate (37.2)% 60.3% (2.7)% Tax Cuts and Jobs Act On December 22, 2017, the Tax Cuts and Jobs Act (the "2017 Tax Act") was signed into law. The 2017 Tax Act includes a broad range of tax reform provisions affecting businesses, including lower corporate tax rates, changes in business deductions, and international tax provisions. In response to the 2017 Tax Act, the U.S. Securities and Exchange Commission staff issued Staff Accounting Bulletin No. 118 ("SAB 118") to address the application of U.S. GAAP in situations where a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the 2017 Tax Act. SAB 118 provides that the measurement period is complete when a company's accounting is complete and that measurement period shall not extend beyond one year from the enactment date. SAB 118 provides guidance for registrants under three scenarios: (i) measurement of certain income tax effects is complete, (ii) measurement of certain income tax effects can be reasonably estimated, and (iii) measurement of certain income tax effects cannot be reasonably estimated. The Company has analyzed the income tax effects of the 2017 Tax Act and determined that measurement of the income tax effects can be reasonably estimated, and, as such, provisional amounts have been recorded. For the fiscal year ended September 30, 2018, the Company recognized income tax benefits of $612.6 million in Income Tax Expense (Benefit) on the Company's Consolidated Statements of Operations related to effects of the 2017 Tax Act, which are comprised of the following: (a) in accordance with Accounting Standards Codification No. 740, which requires deferred taxes to be remeasured in the year of an income tax rate change, the Company recorded a deferred income tax benefit of $897.6 million in the fiscal year ended September 30, 2018 as a result of applying a lower U.S. federal income tax rate to the Company's net deferred tax liabilities as of December 31, 2017; and (b) the 2017 Tax Act also requires a one-time transition tax to be recognized on historical foreign earnings and profits. In the fiscal year ended September 30, 2018, the Company initially recorded a current income tax expense of $310.0 million on historical foreign earnings and profits through December 31, 2017. The Company decreased its provisional transition tax by $25.0 million in the fourth quarter of the fiscal year ended September 30, 2018 as a result of a decline in its foreign cash and cash equivalents position as of September 30, 2018. The Company expects to pay $219.6 million related to the transition tax, which is net of overpayments and tax credits. The transition tax is payable in installments over a six-year period commencing in January 2021. The measurement of income tax effects of the 2017 Tax Act cannot currently be completed due to the effective date of certain aspects of the 2017 Tax Act, including the impact on state taxes. Accordingly, the Company has recognized provisional amounts for the impact of the 2017 Tax Act within the accompanying consolidated financial statements as of and for the fiscal year ended September 30, 2018 and expects to finalize the measurement of all amounts related to the 2017 Tax Act in the fiscal quarter ending December 31, 2018. Prior to the 2017 Tax Act, the Company intended to indefinitely reinvest its foreign cash in foreign investments and foreign operations. After further assessment of the impact of the 2017 Tax Act, the Company reevaluated its position and determined that it was no longer reinvested with respect to foreign subsidiaries whose undistributed earnings are able to be repatriated with minimal to no additional tax impact. Cumulative undistributed earnings of international subsidiaries were $1.9 billion as of September 30, 2018 , $1.1 billion of which is considered permanently reinvested. Deferred income taxes reflect the future tax consequences of differences between the tax bases of assets and liabilities and their financial reporting amounts. Significant components of the Company's deferred tax liabilities (assets) are as follows: September 30, (in thousands) 2018 2017 Merchandise inventories $ 1,189,801 $ 1,519,779 Property and equipment 133,417 150,240 Goodwill and other intangible assets 853,747 1,214,597 Other 747 1,126 Gross deferred tax liabilities 2,177,712 2,885,742 Net operating loss and tax credit carryforwards (421,808 ) (320,180 ) Capital loss carryforwards — (64,346 ) Allowance for doubtful accounts (20,126 ) (25,871 ) Accrued expenses (17,363 ) (36,188 ) Employee and retiree benefits (10,210 ) (17,121 ) Share-based compensation (28,888 ) (59,495 ) Other (49,892 ) (81,009 ) Gross deferred tax assets (548,287 ) (604,210 ) Valuation allowance for deferred tax assets 199,985 211,080 Deferred tax assets, net of valuation allowance (348,302 ) (393,130 ) Net deferred tax liabilities $ 1,829,410 $ 2,492,612 The following tax carryforward information is presented as of September 30, 2018 . The Company had $89.7 million of potential tax benefits from federal net operating loss carryforwards, $75.5 million of which expires in 1 to 19 years, $172.0 million of potential tax benefits from state net operating loss carryforwards expiring in 1 to 20 years, and $49.5 million of potential tax benefits from foreign net operating loss carryforwards, which have varying expiration dates. The Company had $3.9 million of state tax credit carryforwards, $122.9 million in federal alternative minimum tax credit carryforwards, and $2.1 million in foreign alternative minimum tax credit carryforwards. In the fiscal year ended September 30, 2018 , the Company decreased the valuation allowance on deferred tax assets by $11.1 million primarily due to the utilization of capital loss and foreign tax credit carryforwards for which a valuation allowance had been previously recorded. This decrease was offset in part by the additional valuation allowances on certain state and foreign net operating loss carryforwards. In the fiscal year ended September 30, 2017 , the Company increased the valuation allowance on deferred tax assets by $45.5 million primarily due to the addition of certain state and foreign net operating loss carryforwards. Included in the $45.5 million valuation allowance is a $17.1 million valuation allowance that was established in connection with the adoption of ASU 2016-09 (see Note 1). This amount was not recognized in the Consolidated Statement of Operations in the fiscal year ended September 30, 2017. In the fiscal year ended September 30, 2018 and 2017 , tax benefits of $22.7 million and $36.7 million , respectively, related to the exercise of employee stock options and lapses of restricted stock units were recorded in Income Tax (Benefit) Expense in the Company's Consolidated Statement of Operations. In the fiscal year ended September 30, 2016 , there were no tax benefits related to the exercise of employee stock options and lapses of restricted stock units. The tax benefits recognized in the fiscal year ended September 30, 2018 and 2017 are not necessarily indicative of amounts that may arise in future periods. Income tax payments, net of refunds, were $104.0 million , $105.0 million , and $17.5 million in the fiscal years ended September 30, 2018 , 2017 , and 2016 , respectively. The Company and its subsidiaries file income tax returns in the U.S. federal jurisdiction and various states and foreign jurisdictions. With few exceptions, the Company is no longer subject to U.S. federal, state and local, or foreign income tax examinations by tax authorities for years before 2014. As of September 30, 2018 and 2017 , the Company had unrecognized tax benefits, defined as the aggregate tax effect of differences between tax return positions and the benefits recognized in the Company's financial statements, of $112.9 million and $338.4 million , respectively ( $89.4 million and $304.2 million , net of federal benefit, respectively). If recognized in the fiscal years ended September 30, 2018 and 2017 , $71.1 million and $289.2 million , respectively, of these benefits would have reduced income tax expense and the effective tax rate. As of September 30, 2018 and 2017 , included in the unrecognized tax benefits are $14.8 million and $14.5 million of interest and penalties, respectively, which the Company records in Income Tax (Benefit) Expense in the Company's Consolidated Statements of Operations. A reconciliation of the beginning and ending amount of unrecognized tax benefits, excluding interest and penalties, for the periods indicated is as follows: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Unrecognized tax benefits at beginning of period $ 323,869 $ 75,766 $ 44,722 Additions of tax positions of the current year 2,804 252,866 24,145 Additions to tax positions of the prior years 558 1,049 11,840 Reductions of tax positions of the prior years (224,878 ) (668 ) (1,407 ) Settlements with taxing authorities (1,847 ) (3,285 ) (2,589 ) Expiration of statutes of limitations (2,382 ) (1,859 ) (945 ) Unrecognized tax benefits at end of period $ 98,124 $ 323,869 $ 75,766 Included in the additions of unrecognized tax positions in the fiscal year ended September 30, 2017 is approximately $235.1 million for an uncertain tax position related to the $625.0 million civil litigation reserve recognized during the fiscal year ended September 30, 2017 (see Note 13 ). In the fiscal year ended September 30, 2017, this reserve was considered to be non-deductible. In September 2018, the Company made a payment of $625.0 million , plus interest, to resolve this litigation and it was determined that a portion of the settlement is deductible. Accordingly, the Company reduced its uncertain tax position by $224.9 million . During the next 12 months, it is reasonably possible that state tax audit resolutions and the expiration of statutes of limitations could result in a reduction of unrecognized tax benefits by approximately $14.7 million . Other Information In March 2013, the Company issued Warrants (as defined in Note 7 ) in connection with various agreements and arrangements with WBA, as successor in interest to Walgreen Co. ("Walgreens") and Alliance Boots GmbH ("Alliance Boots"). At that time, the Company determined that the Warrants had a fair value of $242.4 million on the date of issuance, which was an estimate of the approximate tax deductible amount that would be deducted ratably on the Company's income tax return over the 10 -year term of the various agreements, and that any value in excess of the initial fair value of the Warrants on the date of issuance would not be tax deductible. The Company reevaluated its position, and in November 2015, the Company received a private letter ruling from the Internal Revenue Service ("IRS"), which entitled it to an income tax deduction equal to the fair value of the Warrants on the date of exercise. As a result, the Company recorded a deferred tax asset and recognized a tax benefit adjustment of approximately $456 million , which represented the estimated benefit from the tax deduction for the increase in the fair value of the Warrants from the issuance date through September 30, 2015. This tax benefit adjustment had a significant impact to the Company's effective tax rate in the fiscal year ended September 30, 2016. In March 2016 and August 2016, the Warrants were exercised in full by WBA. In the aggregate, the total fair value of the Warrants based upon their respective exercise dates was $1,565.9 million . An additional tax benefit of approximately $52 million was recognized primarily related to the change in the fair value of the Warrants from September 30, 2015 to their respective exercise dates in the fiscal year ended September 30, 2016.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets The following is a summary of the changes in the carrying value of goodwill, by reportable segment, for the fiscal years ended September 30, 2018 and 2017 : (in thousands) Pharmaceutical Distribution Services Other Total Goodwill as of September 30, 2016 $ 4,270,550 $ 1,720,947 $ 5,991,497 Goodwill recognized in connection with acquisitions — 54,151 54,151 Goodwill disposed in connection with divestiture — (3,564 ) (3,564 ) Foreign currency translation — 2,197 2,197 Goodwill as of September 30, 2017 4,270,550 1,773,731 6,044,281 Goodwill recognized in connection with acquisitions 641,909 39,352 681,261 Goodwill impairment (59,684 ) — (59,684 ) Foreign currency translation — (1,586 ) (1,586 ) Goodwill as of September 30, 2018 $ 4,852,775 $ 1,811,497 $ 6,664,272 In connection with the Company's annual goodwill impairment test as of July 1, 2018, the Company recorded a goodwill impairment of $59.7 million in its Profarma reporting unit. The fair value of the reporting unit was determined based upon Profarma's publicly-traded stock price, plus an estimated purchase premium. This represents a Level 2 nonrecurring fair value measurement. The following is a summary of other intangible assets: September 30, 2018 September 30, 2017 (dollars in thousands) Weighted Average Remaining Useful Life Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Indefinite-lived trade names $ 685,380 $ — $ 685,380 $ 685,088 $ — $ 685,088 Finite-lived: Customer relationships 14 years 2,549,245 (555,440 ) 1,993,805 2,329,665 (408,636 ) 1,921,029 Trade names and other 13 years 397,946 (129,303 ) 268,643 325,353 (98,189 ) 227,164 Total other intangible assets $ 3,632,571 $ (684,743 ) $ 2,947,828 $ 3,340,106 $ (506,825 ) $ 2,833,281 Amortization expense for finite-lived intangible assets was $181.2 million , $160.5 million , and $152.5 million in the fiscal years ended September 30, 2018 , 2017 , and 2016 , respectively. Amortization expense for finite-lived intangible assets is estimated to be $182.9 million in fiscal 2019 , $175.4 million in fiscal 2020 , $171.4 million in fiscal 2021 , $170.1 million in fiscal 2022 , $169.1 million in 2023 , and $1,393.5 million thereafter.

Debt

Debt	12 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt	Debt Debt consisted of the following: September 30, (in thousands) 2018 2017 Revolving credit note $ — $ — Receivables securitization facility due 2019 500,000 500,000 Term loans due 2020 398,665 547,860 Multi-currency revolving credit facility due 2021 — — Overdraft facility due 2021 (£30,000) 13,269 12,121 $400,000, 4.875% senior notes due 2019 — 398,399 $500,000, 3.50% senior notes due 2021 498,392 497,877 $500,000, 3.40% senior notes due 2024 497,255 496,766 $500,000, 3.25% senior notes due 2025 495,632 494,950 $750,000, 3.45% senior notes due 2027 742,258 — $500,000, 4.25% senior notes due 2045 494,298 494,082 $500,000, 4.30% senior notes due 2047 492,222 — Capital lease obligations 745 — Nonrecourse debt 177,453 — Total debt 4,310,189 3,442,055 Less AmerisourceBergen Corporation current portion 13,976 12,121 Less nonrecourse current portion 137,681 — Total, net of current portion $ 4,158,532 $ 3,429,934 Multi-Currency Revolving Credit Facility The Company has a $1.4 billion multi-currency senior unsecured revolving credit facility ("Multi-Currency Revolving Credit Facility"), which was scheduled to expire in November 2021, with a syndicate of lenders. In October 2018, the Company entered into an amendment to, among other things, extend the maturity to October 2023 and modify certain restrictive covenants, including modifications to allow for indebtedness of foreign subsidiaries. Interest on borrowings under the Multi-Currency Revolving Credit Facility accrues at specified rates based upon the Company's debt rating and ranges from 70 basis points to 110 basis points over CDOR/LIBOR/EURIBOR/Bankers Acceptance Stamping Fee, as applicable ( 91 basis points over CDOR/LIBOR/EURIBOR/Bankers Acceptance Stamping Fee as of September 30, 2018 ) and from 0 basis points to 10 basis points over the alternate base rate and Canadian prime rate, as applicable. The Company pays facility fees to maintain the availability under the Multi-Currency Revolving Credit Facility at specified rates based on its debt rating, ranging from 5 basis points to 15 basis points , annually, of the total commitment ( 9 basis points as of September 30, 2018 ). The Company may choose to repay or reduce its commitments under the Multi-Currency Revolving Credit Facility at any time. The Multi-Currency Revolving Credit Facility contains covenants, including compliance with a financial leverage ratio test, as well as others that impose limitations on, among other things, indebtedness of subsidiaries and asset sales, with which the Company was compliant as of September 30, 2018 . Commercial Paper Program The Company has a commercial paper program whereby it may from time to time issue short-term promissory notes in an aggregate amount of up to $1.4 billion at any one time. Amounts available under the program may be borrowed, repaid, and re-borrowed from time to time. The maturities on the notes will vary, but may not exceed 365 days from the date of issuance. The notes will bear interest, if interest bearing, or will be sold at a discount from their face amounts. The commercial paper program does not increase the Company's borrowing capacity as it is fully backed by the Company's Multi-Currency Revolving Credit Facility. There were no borrowings outstanding under the commercial paper program as of September 30, 2018 and 2017 . Receivables Securitization Facility The Company has a $1,450 million receivables securitization facility ("Receivables Securitization Facility"), which was scheduled to expire in November 2019. In October 2018, the Company extended the maturity date to October 2021. The Company has available to it an accordion feature whereby the commitment on the Receivables Securitization Facility may be increased by up to $250 million , subject to lender approval, for seasonal needs during the December and March quarters. Interest rates are based on prevailing market rates for short-term commercial paper or LIBOR, plus a program fee. The Company pays a customary unused fee at prevailing market rates, annually, to maintain the availability under the Receivables Securitization Facility. In connection with the Receivables Securitization Facility, AmerisourceBergen Drug Corporation sells on a revolving basis certain accounts receivable to Amerisource Receivables Financial Corporation, a wholly-owned special purpose entity, which in turn sells a percentage ownership interest in the receivables to financial institutions and commercial paper conduits sponsored by financial institutions. AmerisourceBergen Drug Corporation is the servicer of the accounts receivable under the Receivables Securitization Facility. As sold receivables are collected, additional receivables may be sold up to the maximum amount available under the facility. The facility is a financing vehicle utilized by the Company because it generally offers an attractive interest rate relative to other financing sources. The Company securitizes its trade accounts, which are generally non-interest bearing, in transactions that are accounted for as borrowings. The Receivables Securitization Facility contains similar covenants to the Multi-Currency Revolving Credit Facility, with which the Company was compliant as of September 30, 2018 . Revolving Credit Note and Overdraft Facility The Company has an uncommitted, unsecured line of credit available to it pursuant to a revolving credit note ("Revolving Credit Note"). The Revolving Credit Note provides the Company with the ability to request short-term unsecured revolving credit loans from time to time in a principal amount not to exceed $75 million . The Revolving Credit Note may be decreased or terminated by the bank or the Company at any time without prior notice. The Company also has a £30 million uncommitted U.K. overdraft facility ("Overdraft Facility"), which expires in February 2021, to fund short-term normal trading cycle fluctuations related to its MWI business. Term Loans In February 2015, the Company entered into a $1.0 billion variable-rate term loan ("February 2015 Term Loan"), which matures in 2020. Through September 30, 2018 , the Company elected to make principal payments, prior to the scheduled repayment dates, of $925.0 million on the February 2015 Term Loan, and as a result, the Company's next required principal payment is due upon maturity. The February 2015 Term Loan bears interest at a rate equal either to a base rate, plus a margin, or LIBOR, plus a margin. The margin is based on the public debt ratings of the Company and ranges from 75 basis points to 125 basis points over LIBOR ( 100 basis points as of September 30, 2018 ) and 0 basis points to 25 basis points over a base rate. The February 2015 Term Loan contains similar covenants to the Multi-Currency Revolving Credit Facility, with which the Company was compliant as of September 30, 2018 . In November 2015, the Company entered into a $1.0 billion variable-rate term loan ("November 2015 Term Loan"), which matures in 2020. Through September 30, 2018 , the Company made a scheduled principal payment, as well as other principal payments prior to the scheduled repayment dates totaling $675.0 million on the November 2015 Term Loan, and as a result, the Company's next required principal payment is due upon maturity. The November 2015 Term Loan bears interest at a rate equal either to a base rate, plus a margin, or LIBOR, plus a margin. The margin is based on the public debt ratings of the Company and ranges from 75 basis points to 125 basis points over LIBOR ( 100 basis points as of September 30, 2018 ) and 0 basis points to 25 basis points over a base rate. The November 2015 Term Loan contains similar covenants to the Multi-Currency Revolving Credit Facility, with which the Company was compliant as of September 30, 2018 . The February 2015 and November 2015 Term Loans (collectively, the "Term Loans") were scheduled to mature in November 2020 and February 2020, respectively. In October 2018, the Company refinanced the Term Loans by issuing a new variable-rate term loan ("October 2018 Term Loan"), which matures in October 2020. The October 2018 Term Loan bears interest at a rate equal to a base rate or LIBOR, plus a margin of 65 basis points. The October 2018 Term Loan contains similar covenants to the Multi-Currency Revolving Credit Facility. Senior Notes In December 2017, the Company issued $750 million of 3.45% senior notes due December 15, 2027 (the "2027 Notes") and $500 million of 4.30% senior notes due December 15, 2047 (the "2047 Notes"). The 2027 Notes were sold at 99.76% of the principal amount and have an effective yield of 3.48% . The 2047 Notes were sold at 99.51% of the principal amount and have an effective yield of 4.33% . Interest on the 2027 Notes and the 2047 Notes is payable semi-annually in arrears and commenced on June 15, 2018 . The 2027 and 2047 Notes rank pari passu to the Company's other senior notes, the Multi-Currency Revolving Credit Facility, the Revolving Credit Note, the Overdraft Facility, and the Term Loans. The Company used the proceeds from the 2027 Notes and the 2047 Notes to finance the early retirement of the $400 million of 4.875% senior notes that were due in 2019, including the payment of a $22.3 million prepayment premium, and to finance the acquisition of H.D. Smith, which was completed in January 2018 (see Note 2 ). In May 2017, the Company repaid the $600 million of 1.15% senior notes that became due. The senior notes are collectively referred to as the "Notes." Interest on the Notes is payable semiannually in arrears. The Notes were sold at small discounts to the principal amounts and, therefore, have effective yields that are greater than the stated interest rates in the table above. Costs incurred in connection with the issuance of the Notes were deferred and are being amortized over the terms of the Notes. The indentures governing the Notes contain restrictions and covenants, which include limitations on additional indebtedness; distributions to stockholders; the repurchase of stock and the making of other restricted payments; issuance of preferred stock; creation of certain liens; transactions with subsidiaries and other affiliates; and certain corporate acts such as mergers, consolidations, and the sale of substantially all assets. An additional covenant requires compliance with a financial leverage ratio test, with which the Company was compliant as of September 30, 2018 . Nonrecourse Debt The Company consolidated the short-term and long-term debt of Profarma and the specialty joint venture in connection with the incremental investments made in January 2018 (see Note 2 and Note 3 ). Nonrecourse debt is repaid solely from the Brazil subsidiaries' cash flows and such debt agreements provide that the repayment of the loans (and interest thereon) is secured solely by the capital stock, physical assets, contracts, and cash flows of the Brazil subsidiaries. Other Information Scheduled future principal payments of debt are $148.8 million in fiscal 2019, $595.7 million in fiscal 2020, $336.9 million in fiscal 2021, $500.0 million in fiscal 2022, none in fiscal 2023, and $2.8 billion thereafter. Interest paid on the above indebtedness during the fiscal years ended September 30, 2018 , 2017 , and 2016 was $162.1 million , $125.3 million , and $123.5 million , respectively. Total amortization of financing fees and the accretion of original issue discounts, which are recorded as components of Interest Expense, Net on the Consolidated Statements of Operations, were $7.7 million , $6.2 million , and $6.3 million , for the fiscal years ended September 30, 2018 , 2017 , and 2016 , respectively.

Stockholders' Equity and Weight

Stockholders' Equity and Weighted Average Common Shares Outstanding	12 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Stockholders' Equity and Weighted Average Common Shares Outstanding	Stockholders' Equity and Weighted Average Common Shares Outstanding The authorized capital stock of the Company consists of 600,000,000 shares of common stock, par value $0.01 per share (the "common stock"), and 10,000,000 shares of preferred stock, par value $0.01 per share (the "preferred stock"). The board of directors is authorized to provide for the issuance of shares of preferred stock in one or more series with various designations and preferences and relative, participating, optional, or other special rights and qualifications, limitations, or restrictions. Except as required by law, or as otherwise provided by the board of directors of the Company, the holders of preferred stock will have no voting rights and will not be entitled to notice of meetings of stockholders. Holders of preferred stock will be entitled to receive, when declared by the board of directors, out of legally available funds, dividends at the rates fixed by the board of directors for the respective series of preferred stock, and no more, before any dividends will be declared and paid, or set apart for payment, on common stock with respect to the same dividend period. No shares of preferred stock have been issued as of September 30, 2018 . The holders of the Company's common stock are entitled to one vote per share and have the exclusive right to vote for the board of directors and for all other purposes as provided by law. Subject to the rights of holders of the Company's preferred stock, holders of common stock are entitled to receive ratably on a per share basis such dividends and other distributions in cash, stock, or property of the Company as may be declared by the board of directors from time to time out of the legally available assets or funds of the Company. The following illustrates the components of Accumulated Other Comprehensive Loss, net of income taxes: September 30, (in thousands) 2018 2017 Pension and postretirement adjustments $ (5,065 ) $ (4,186 ) Foreign currency translation (74,811 ) (92,164 ) Other 623 500 Total accumulated other comprehensive loss $ (79,253 ) $ (95,850 ) In August 2013, the Company's board of directors authorized a share repurchase program allowing the Company to purchase up to $750 million of its outstanding shares of common stock, subject to market conditions. During the six months ended March 31, 2016, the Company purchased 1.1 million shares of its common stock for a total of $100.0 million under this program. In May 2016, the Company's board of directors authorized a share purchase program that, together with availability remaining under the existing August 2013 share repurchase program, permitted the Company to purchase up to $750 million of its outstanding shares of common stock, subject to market conditions. In September 2016, the Company entered into an Accelerated Share Repurchase ("ASR") transaction with a financial institution and paid $400.0 million for the delivery of 4.5 million shares of its common stock. The initial payment of $400.0 million funded stock purchases of $380.0 million and a share holdback of $20.0 million . The ASR transaction was settled in November 2016, at which time the financial institution delivered an additional 0.5 million shares of the Company's common stock. The number of shares ultimately received was based upon the volume-weighted average price of the Company's common stock during the term of the ASR. The Company applied the 4.5 million shares from the ASR to the May 2016 share repurchase program. In addition to the ASR, the Company purchased 2.9 million shares of its common stock in fiscal 2016 for a total of $231.2 million under this program. During the fiscal year ended September 30, 2017, the Company purchased 2.1 million shares of its common stock (included 0.5 million shares of common stock received as part of the settlement of the ASR) for a total of $118.8 million to complete its authorization under this program. In November 2016, the Company's board of directors authorized a share repurchase program allowing the Company to purchase up to $1.0 billion of its outstanding shares of common stock, subject to market conditions. During the fiscal year ended September 30, 2017, the Company purchased 2.7 million shares of its common stock for a total of $211.1 million under this program. During the fiscal year ended September 30, 2018, the Company purchased 7.7 million shares of its common stock for a total of $663.1 million , which included $24.0 million of September 2018 purchases that cash settled in October 2018. As of September 30, 2018, the Company had $125.8 million of availability remaining under this program. In October 2018, the Company's board of directors authorized a new share repurchase program allowing the Company to purchase up to $1.0 billion of its outstanding shares of common stock, subject to market conditions. Warrants and Related Hedging Activity In March 2013, the Company and WBA entered into various agreements and arrangements pursuant to which subsidiaries of WBA were granted the right to purchase a minority equity position in the Company, beginning with the right, but not the obligation, to purchase up to 19,859,795 shares of the Company's common stock in open market transactions (approximately 7% of the Company's common stock on a fully diluted basis as of the date of issuance of the Warrants described below, assuming their exercise in full). In connection with these arrangements, wholly-owned subsidiaries of WBA were issued (a) warrants to purchase up to an aggregate of 22,696,912 shares of the Company's common stock at an exercise price of $51.50 per share, exercisable during a six -month period beginning in March 2016 (the "2016 Warrants"), and (b) warrants to purchase up to an aggregate of 22,696,912 shares of the Company's common stock at an exercise price of $52.50 per share, exercisable during a six -month period beginning in March 2017 (the "2017 Warrants" and, together with the 2016 Warrants, the "Warrants"). In June 2013, the Company commenced a strategy to mitigate the dilutive effect of the Warrants upon exercise. Prior to fiscal 2016, the Company purchased 18.8 million shares of its common stock for $1,774.1 million under special share repurchase programs. During the fiscal year ended September 30, 2016, the Company purchased 26.3 million shares of its common stock for a total of $1,535.1 million under a special share repurchase program. In March 2016, the 2016 Warrants were exercised by WBA for $1,168.9 million in cash. The shares issued for the 2016 Warrants were from the Company's treasury stock on a first-in, first-out basis, and were originally purchased for $866.0 million . The Company recognized a reissuance gain in Additional Paid-in Capital of $302.9 million . In August 2016, the Company and WBA amended the 2017 Warrants so that they became exercisable in whole or in part during the six -month period beginning in August 2016 at an exercise price of $52.50 . In August 2016, the 2017 Warrants were exercised by WBA for $1,191.6 million in cash. The shares issued for the 2017 Warrants were from the Company's treasury stock on a first-in, first-out basis, and were originally purchased for $1,157.5 million . The Company recognized a reissuance gain in Additional Paid-in Capital of $34.1 million . Common Shares Outstanding Basic earnings per share is computed by dividing net income attributable to AmerisourceBergen Corporation by the weighted average number of shares of common stock outstanding during the periods presented. Diluted earnings per share is computed by dividing net income attributable to AmerisourceBergen Corporation by the weighted average number of shares of common stock outstanding, plus the dilutive effect of stock options, restricted stock, restricted stock units, the unsettled ASR transaction, and the Warrants during the periods presented. The following illustrates the components of diluted weighted average shares outstanding: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Weighted average common shares outstanding - basic 217,872 218,375 212,206 Effect of dilutive securities - stock options, restricted stock, restricted stock units, and the unsettled ASR transaction 2,464 3,227 3,338 Dilutive effect of the Warrants — — 10,415 Weighted average common shares outstanding - diluted 220,336 221,602 225,959 The potentially dilutive stock options, restricted stock, restricted stock units, the unsettled ASR transaction, and the Warrants that were antidilutive for the fiscal years ended September 30, 2018 , 2017 , and 2016 were 3.2 million , 4.1 million , and 3.1 million , respectively.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions WBA owns more than 10% of the Company's outstanding common stock and is, therefore, considered a related party. The Company operates under various agreements and arrangements with WBA, including a pharmaceutical distribution agreement pursuant to which the Company distributes pharmaceutical products to WBA and an agreement that provides the Company the ability to access favorable economic pricing and generic products through a generic purchasing services arrangement with Walgreens Boots Alliance Development GmbH. Both of these agreements expire in 2026. Revenue from the various agreements and arrangements with WBA was $54.7 billion , $45.4 billion , and $43.4 billion in the fiscal years ended September 30, 2018 , 2017 , and 2016 , respectively. The Company's receivable from WBA, net of incentives, was $5.6 billion and $5.0 billion as of September 30, 2018 and 2017 , respectively.

Retirement and Other Benefit Pl

Retirement and Other Benefit Plans	12 Months Ended
	Sep. 30, 2018
Retirement Benefits [Abstract]
Retirement and Other Benefit Plans	Retirement and Other Benefit Plans The Company sponsors various retirement benefit plans and a deferred compensation plan covering eligible employees. The Compensation and Succession Planning Committee ("Compensation Committee") of the Company's board of directors has delegated the administration of the Company's retirement and other benefit plans to its Benefits Committee, an internal committee, comprised of senior finance, human resources, and legal executives. The Benefits Committee is responsible for the investment options under the Company's savings plans, as well as performance of the investment advisers and plan administrators. Defined Benefit Plans The Company approved the termination, effective August 1, 2014, of a salaried defined benefit pension plan, under which approximately 3,200 participants, including 500 active employees, had accrued benefits. In fiscal 2015, the Company obtained regulatory approval from the IRS to settle the plan. In December 2015, the Company completed the settlement of plan benefits through the combination of lump-sum distributions to participants and the purchase of a nonparticipating annuity contract, which transferred the remaining obligation from the plan. Plan assets were sufficient to satisfy the obligations of the plan. During the fiscal year ended September 30, 2016, the Company recorded a pension settlement charge of $47.6 million , which primarily consisted of the recognition of unrecognized actuarial losses that were included in Accumulated Other Comprehensive Loss, net of the related deferred tax assets. In June 2016, the Company transferred the surplus plan assets to its defined contribution 401(k) plan and recorded a charge of $17.1 million in Employee Severance, Litigation, and Other in the Company's Consolidated Statement of Operations. Defined Contribution Plans The Company sponsors the AmerisourceBergen Employee Investment Plan (the "Plan"), which is a defined contribution 401(k) plan covering salaried and certain hourly employees. Eligible participants may contribute to the plan from 1% to 50% of their regular compensation before taxes. Prior to January 1, 2017, the Company contributed $1.00 for each $1.00 invested by the participant up to the first 3% of the participant's salary and $0.50 for each additional $1.00 invested by the participant of up to an additional 2% of salary. Effective January 1, 2017, the Company contributes $1.00 for each $1.00 invested by the participant up to the first 3% of the participant's salary. Effective January 1, 2019, the Company will contribute $1.00 for each $1.00 invested by the participant up to the first 3% of the participant's salary and $0.50 for each additional $1.00 invested by the participant of up to an additional 2% of salary. An additional discretionary contribution, in an amount not to exceed the limits established by the Internal Revenue Code ("IRC"), may also be made depending upon the Company's performance. In connection with the termination of the salaried defined benefit plan, as discussed above, $17.1 million was transferred to the 401(k) plan in June 2016. In March 2017, the funds were contributed to participants who were eligible to participate in the 401(k) plan as of December 31, 2015, based upon their eligible calendar 2016 earnings. Based on the Company's performance in fiscal 2018, the Company recognized an expense for a discretionary contribution to the Plan in the fiscal year ended September 30, 2018. There was no discretionary contribution recognized for in the fiscal year ended September 30, 2017. All contributions are invested at the direction of the employee in one or more funds. All contributions vest immediately except for the discretionary contributions made by the Company, which vest in full after five years of credited service. The Company also sponsors the AmerisourceBergen Corporation Benefit Restoration Plan. This unfunded plan provides benefits to selected key management, including all of the Company's executive officers. Prior to January 1, 2017, the Company contributed an amount equal to 4% of the participant's total cash compensation to the extent that his or her compensation exceeded the annual compensation limit established by Section 401(a) (17) of the IRC. Effective January 1, 2017, this plan provides eligible participants with an annual amount equal to 3% of the participant's total cash compensation to the extent that his or her compensation exceeds the annual compensation limit established by Section 401(a) (17) of the IRC. Effective January 1, 2019, this plan will provide eligible participants with an annual amount equal to 4% of the participant's total cash compensation to the extent that his or her compensation exceeds the annual compensation limit established by Section 401(a) (17) of the IRC. Costs of the defined contribution plans charged to expense for the fiscal years ended September 30, 2018 , 2017 , and 2016 were $37.9 million , $28.3 million , and $34.4 million , respectively. Deferred Compensation Plan The Company sponsors the AmerisourceBergen Corporation 2001 Deferred Compensation Plan. This unfunded plan, under which 2.96 million shares of common stock are authorized for issuance, allows eligible officers, directors, and key management employees to defer a portion of their annual compensation. The amount deferred may be allocated by the employee to cash, mutual funds, or stock credits. Stock credits, including dividend equivalents, are equal to the full and fractional number of shares of common stock that could be purchased with the participant's compensation allocated to stock credits based upon the average of closing prices of common stock during each month, plus, at the discretion of the board of directors, up to one-half of a share of common stock for each full share credited. Stock credit distributions are made in shares of common stock. No shares of common stock have been issued under the deferred compensation plan through September 30, 2018 . The Company's liability relating to its deferred compensation plan as of September 30, 2018 and 2017 was $27.5 million and $26.3 million , respectively.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation Stock Options The Company's employee stock option plans provide for the granting of incentive and nonqualified stock options to acquire shares of common stock to employees at a price not less than the fair market value of the common stock on the date the option is granted. Option terms and vesting periods are determined at the date of grant by the Compensation Committee of the board of directors. Employee options generally vest ratably, in equal amounts, over a four -year service period and expire in seven years. The Company's non-employee director stock option plans provide for the granting of nonqualified stock options to acquire shares of common stock to non-employee directors at the fair market value of the common stock on the date of the grant. Non-employee director options vest ratably, in equal amounts, over a three -year service period and expire in ten years. Non-employee director options have not been granted since February 2011. As of September 30, 2018 , employee and non-employee director stock options for an additional 15.6 million shares may be granted under the AmerisourceBergen Corporation Omnibus Incentive Plan (the "Plan"). The estimated fair value of options granted is expensed on a straight-line basis over the requisite service periods of the awards and are net of estimated forfeitures. The Company estimates the fair values of option grants using a binomial option pricing model. Expected volatilities are based upon the historical volatility of the Company's common stock and other factors, such as implied market volatility. The Company uses historical exercise data, taking into consideration the optionees' ages at grant date, to estimate the terms for which the options are expected to be outstanding. The Company anticipates that the terms of options granted in the future will be similar to those granted in the past. The risk-free rates during the terms of such options are based upon the U.S. Treasury yield curve in effect at the time of grant. The weighted average fair values of the options granted during the fiscal years ended September 30, 2018 , 2017 , and 2016 were $14.16 , $13.57 , and $17.43 , respectively. The following weighted average assumptions were used to estimate the fair values of options granted: Fiscal Year Ended September 30, 2018 2017 2016 Risk-free interest rate 1.89% 1.26% 1.40% Expected dividend yield 1.96% 1.80% 1.38% Volatility of common stock 26.54% 26.78% 25.05% Expected life of the options 3.76 years 3.74 years 3.72 years Changes to the above valuation assumptions could have a significant impact on share-based compensation expense. During the fiscal years ended September 30, 2018 , 2017 , and 2016 , the Company recognized stock option expense of $22.6 million , $28.6 million , and $33.1 million , respectively. A summary of the Company's stock option activity and related information for its option plans for the fiscal year ended September 30, 2018 is presented below: (in thousands, except exercise price and contractual term) Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value Outstanding as of September 30, 2017 10,287 $70 4 years $ 170,856 Granted 1,538 $78 Exercised (2,742 ) $51 Forfeited (604 ) $84 Expired (58 ) $95 Outstanding as of September 30, 2018 8,421 $77 4 years $ 142,557 Exercisable as of September 30, 2018 4,561 $72 3 years $ 98,863 Expected to vest after September 30, 2018 3,732 $82 5 years $ 41,982 The intrinsic value of stock option exercises during the fiscal years ended September 30, 2018 , 2017 , and 2016 was $116.7 million , $116.6 million , and $120.9 million , respectively. A summary of the status of the Company's nonvested options as of September 30, 2018 and changes during the fiscal year ended September 30, 2018 is presented below: (in thousands, except grant date fair value) Options Weighted Average Grant Date Fair Value Nonvested as of September 30, 2017 4,752 $15 Granted 1,538 $14 Vested (1,826 ) $14 Forfeited (604 ) $15 Nonvested as of September 30, 2018 3,860 $15 During the fiscal years ended September 30, 2018 , 2017 , and 2016 , the total fair values of options vested were $25.8 million , $25.2 million , and $24.4 million , respectively. Expected future compensation expense relating to the 3.9 million nonvested options outstanding as of September 30, 2018 is $25.8 million , which will be recognized over a weighted average period of 2.1 years. Restricted Stock Units Restricted stock units vest in full after three years. The estimated fair value of restricted stock units under the Company's restricted stock unit plans is determined by the product of the number of shares granted and the grant date market price of the Company's common stock. The estimated fair value of restricted stock units is expensed on a straight-line basis over the requisite service period and are net of estimated forfeitures. During the fiscal years ended September 30, 2018 , 2017 , and 2016 , the Company recognized restricted stock unit expense of $26.8 million , $25.1 million , and $19.5 million , respectively. A summary of the status of the Company's nonvested restricted stock units as of September 30, 2018 and changes during the fiscal year ended September 30, 2018 are presented below: (in thousands, except grant date fair value) Restricted Stock Units Weighted Average Grant Date Fair Value Nonvested as of September 30, 2017 819 $84 Granted 526 $78 Vested (173 ) $91 Forfeited (149 ) $81 Nonvested as of September 30, 2018 1,023 $80 During the fiscal years ended September 30, 2018 , 2017 , and 2016 , the total fair values of restricted stock units vested were $15.8 million , $13.8 million , and $17.8 million , respectively. Expected future compensation expense relating to the 1.0 million restricted stock units outstanding as of September 30, 2018 is $29.1 million , which will be recognized over a weighted average period of 1.3 years. Performance Stock Units Performance stock units are granted to certain executive employees under the Plan and represent common stock potentially issuable in the future. Performance stock units vest at the end of a three -year performance period based upon achievement of specific performance goals. Based upon the extent to which the targets are achieved, vested shares for awards granted prior to fiscal 2018 may range from 0% to 150% of the target award amount. For awards granted beginning in fiscal 2018, vested shares may range from 0% to 200% of the target award amount. The fair value of performance stock units is determined by the grant date market price of the Company's common stock. Compensation expense associated with nonvested performance stock units is recognized over the requisite service period and is dependent on the Company's periodic assessment of the probability of the targets being achieved and its estimate of the number of shares that will ultimately be issued. During the fiscal years ended September 30, 2018 , 2017 , and 2016 , the Company recognized performance stock expense of $12.8 million , $8.4 million , and $12.3 million , respectively. A summary of the status of the Company's nonvested performance stock units as of September 30, 2018 and changes during the fiscal year ended September 30, 2018 is presented below (based upon target award amounts). (in thousands, except grant date fair value) Performance Stock Units Weighted Average Grant Date Fair Value Nonvested as of September 30, 2017 201 $85 Granted 150 $78 Vested (80 ) $98 Forfeited (27 ) $79 Nonvested as of September 30, 2018 244 $77 Shares that vested over the three -year performance period ended September 30, 2018 were distributed to employees in November 2018 . Employee Stock Purchase Plan The AmerisourceBergen Corporation Employee Stock Purchase Plan provides for an aggregate of 4,000,000 shares of common stock that may be sold to eligible employees (generally defined as employees with at least 30 days of service with the Company). Prior to July 1, 2018, the participants could elect to have the Company withhold up to 25% of his or her base salary to purchase shares of the Company's common stock at a price equal to 95% of the fair market value of the stock on the last business day of each six -month purchase period. Effective July 1, 2018, the participants may elect to have the Company withhold up to 25% of his or her base salary to purchase shares of the Company's common stock at a price equal to 85% of the fair market value of the stock on the last business day of each six-month period. Each participant is limited to $25,000 of purchases during each calendar year. During the fiscal years ended September 30, 2018 , 2017 , and 2016 , the Company acquired 72,198 shares, 75,904 shares, and 71,016 shares, respectively, from the open market for issuance to participants in this plan. As a result of increasing in the discount provided to employees from 5% to 15% , the Company began recognizing the 15% discount as an expense in Distribution, Selling, and Administrative in the Statement of Operations. Prior to the increase in the discount, the Company recognized the discount in Additional Paid-in Capital in the Statement of Stockholders' Equity.

Leases and Other Commitments

Leases and Other Commitments	12 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Leases and Other Commitments	Leases and Other Commitments The Company has long-term leases for facilities and equipment. In the normal course of business, leases are generally renewed or replaced by other leases. Certain leases include escalation clauses. During the fiscal years ended September 30, 2018 , 2017 , 2016 , the Company recorded rental expense of $114.9 million , $80.7 million , and $88.8 million , respectively, in Distribution, Selling, and Administrative in the Consolidated Statements of Operations. As of September 30, 2018 , future minimum rental payments under noncancelable operating leases and financing obligations were as follows: Payments Due by Fiscal Year (in thousands) Operating Leases Financing Obligations 1 Total 2019 $ 89,589 $ 26,561 $ 116,150 2020 84,689 28,137 112,826 2021 75,929 27,974 103,903 2022 64,064 25,591 89,655 2023 54,168 24,401 78,569 Thereafter 143,714 107,146 250,860 Total minimum lease payments $ 512,153 $ 239,810 $ 751,963 1 Represents the portion of future minimum lease payments relating to facility leases where the Company was determined to be the accounting owner (see Note 1). These payments are recognized as reductions to the financing obligation and as interest expense and exclude the future non-cash termination of the financing obligation. The 2017 Tax Act requires a one-time transition tax to be recognized on historical foreign earnings and profits. The Company currently estimates that its liability related to the transition tax is approximately $219.6 million , net of tax credits and refunds, as of September 30, 2018 , which is payable in installments over a six-year period commencing in January 2021. The Company outsources to IBM Global Services a significant portion of its data center operations. The remaining commitment under the Company's arrangement, which expires in January 2021 , is approximately $33.7 million as of September 30, 2018 , of which $15.0 million represents the Company's commitment in fiscal 2019 .

Employee Severance, Litigation,

Employee Severance, Litigation, and Other	12 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Employee Severance, Litigation, and Other	Employee Severance, Litigation, and Other The following illustrates the charges incurred by the Company relating to Employee Severance, Litigation, and Other for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Employee severance $ 36,694 $ 7,767 $ 38,786 Litigation and opioid-related costs 61,527 917,573 — Transfer of surplus plan assets — — 17,149 Customer contract dispute settlements — — 13,000 Other 85,299 33,987 33,976 Total employee severance, litigation, and other $ 183,520 $ 959,327 $ 102,911 Employee severance costs in the fiscal year ended September 30, 2018 primarily related to position eliminations resulting from the Company's business transformation efforts and restructuring activities related to its consulting business. Employee severance costs in the fiscal year ended September 30, 2017 primarily related to position eliminations as the Company began to reorganize to further align the organization to its customers' needs. Employee severance costs in the fiscal year ended September 30, 2016 primarily related to position eliminations as the Company reorganized certain of its business units and corporate functions to improve operating efficiency. Employees receive their severance benefits over a period of time, generally not in excess of 12 months, or in the form of a lump-sum payment. Litigation and opioid-related costs in the fiscal year ended September 30, 2018 primarily related to opioid lawsuits, investigations, and related initiatives. Litigation and opioid-related costs in the fiscal year ended September 30, 2017 primarily related to litigation settlements and accruals. During the fiscal year ended September 30, 2016, the Company recognized a $17.1 million charge related to the transfer of surplus assets from the Company's settled salaried defined benefit pension plan to its defined contribution 401(k) plan and $13.0 million of costs related to customer contract extensions (primarily related to the settlement of certain disputed items). Other costs in the fiscal year ended September 30, 2018 included $33.9 million of acquisition-related deal and integration costs, $33.0 million related to the Company's business transformation efforts, and $18.4 million of other restructuring initiatives. Other costs in the fiscal year ended September 30, 2017 included $17.0 million of acquisition-related deal and integration costs, $13.3 million of other restructuring initiatives, and $3.7 million related to the Company's business transformation efforts. Other costs in the fiscal year ended September 30, 2016 included $19.2 million of acquisition-related deal and integration costs and $14.7 million of other restructuring initiatives.

Legal Matters and Contingencies

Legal Matters and Contingencies	12 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Legal Matters and Contingencies	Legal Matters and Contingencies In the ordinary course of its business, the Company becomes involved in lawsuits, administrative proceedings, government subpoenas, government investigations, and other disputes, including antitrust, commercial, environmental, product liability, intellectual property, regulatory, employment discrimination, and other matters. Significant damages or penalties may be sought from the Company in some matters, and some matters may require years for the Company to resolve. The Company records a reserve for these matters when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. With respect to the specific legal proceedings and claims described below, unless otherwise noted, the amount or range of possible losses is not reasonably estimable. There can be no assurance that the settlement, resolution, or other outcome of one or more matters, including the matters set forth below, during any subsequent reporting period will not have a material adverse effect on the Company's results of operations or cash flows for that period or on the Company's financial condition. For those matters for which the Company has not recognized a liability, the Company cannot predict the outcome of their impact on the Company as uncertainty remains with regard to whether such matters will proceed to trial, whether settlements will be reached, and the amount and terms of any such settlements. Outcomes may include settlements in significant amounts that are not currently estimable, limitations on the Company's conduct, the imposition of corporate integrity obligations, and/or other civil and criminal penalties. Government Enforcement and Related Litigation Matters The Company is, at various times, involved in government investigations and litigation arising from the marketing, promotion, sale, and dispensing of pharmaceutical products in the United States. Some of these investigations originate through what are known as qui tam complaints of the Federal False Claims Act. The qui tam provisions of the Federal False Claims Act and various state and local civil False Claims Acts permit a private person, known as a "relator" or whistleblower, to file civil actions under these statutes on behalf of the federal, state, and local governments. Qui tam complaints are initially filed by the relator under seal (or on a confidential basis) and the filing of the complaint imposes obligations on government authorities to investigate the allegations in the complaint and to determine whether or not to intervene in the action. Qui tam complaints remain sealed until the court in which the case was filed orders otherwise. Under the Federal False Claims Act, the government (or relators who pursue the claims without the participation of the government in the case) may seek to recover up to three times the amount of damages in addition to a civil penalty for each purported false claim submitted to the government for payment. Generally speaking, these cases take several years for the investigation to be completed and, ultimately, to be resolved (either through litigation or settlement) after the complaint is unsealed. In addition, some states have pursued investigations under state false claims statutes or consumer protection laws, either in conjunction with a government investigation or separately. There is often collateral litigation that arises from public disclosures of government investigations, including the filing of class action lawsuits by third party payors or by shareholders alleging violations of the securities laws. Subpoenas and Ongoing Investigations From time to time, the Company receives subpoenas or requests for information from various government agencies relating to the Company's business or to the business of a customer, supplier, or other industry participant. The Company generally responds to such subpoenas and requests in a cooperative manner. These responses often require time and effort and can result in considerable costs being incurred by the Company. Most of these matters are resolved without incident; however, such subpoenas or requests can lead to the assertion of claims or the commencement of civil or criminal legal proceedings against the Company and other members of the healthcare industry, as well as to substantial settlements. Since fiscal 2012, the Company and its subsidiary AmerisourceBergen Specialty Group ("ABSG") have been responding to subpoenas from the U.S. Attorney's Office for the Eastern District of New York ("USAO-EDNY") requesting production of documents and information relating to the pre-filled syringe program of ABSG’s subsidiary Medical Initiatives, Inc., ABSG's oncology distribution center, its group purchasing organization for oncologists, and intercompany transfers of certain oncology products. Medical Initiatives, Inc. voluntarily ceased operations in early 2014. On September 27, 2017, pursuant to the terms of a plea agreement, ABSG entered a guilty plea to a one-count strict-liability misdemeanor violation of the Federal Food, Drug, and Cosmetic Act in the United States District Court of the Eastern District of New York. Under the terms of the agreement, which were approved by the Court, ABSG paid a total criminal fine and forfeiture of $260.0 million in fiscal 2017. The guilty plea resolves the federal criminal investigation related to the failure of Medical Initiatives, Inc. to duly register with the FDA. The Company also entered into a Compliance Agreement with the United States Department of Justice for a period of three years. During the year ended September 30, 2017, the Company recognized the $260.0 million settlement in Employee Severance, Litigation, and Other on the Company's Consolidated Statements of Operations. The USAO-EDNY also pursued alleged civil claims under the False Claims Act. As previously disclosed, ABSG reached an agreement in principle with the USAO-EDNY during the quarter ended December 31, 2017, which the Company expected would resolve the alleged civil claims in their entirety. In the fiscal quarter ended September 30, 2018, the Company reached final terms of the settlement agreement with the USAO-EDNY, resolved potential administrative action by the Office of Inspector General of the U.S. Department of Health and Human Services by entering into a Corporate Integrity Agreement, and obtained dismissal with prejudice of the potential civil claims. The Corporate Integrity Agreement has a five-year term, which commenced on September 28, 2018, and requires, among other things, the maintenance of a compliance program, an independent review organization and a financial recoupment program. Pursuant to the terms of the settlement agreement with the USAO-EDNY, ABSG made a payment on September 28, 2018 to resolve the civil litigation without making any admission of liability in the amount of $625.0 million , plus interest from December 1, 2017. As previously disclosed, as a result of the agreement in principle, the Company had previously accrued a reserve in the amount of $625.0 million in the fiscal year ended September 30, 2017. The reserve was recognized in Employee Severance, Litigation, and Other on the Company's Statement of Operations and in Accrued Expenses and Other on the Company's Consolidated Balance Sheet. The Company’s subsidiary U.S. Bioservices Corporation ("U.S. Bio") settled claims with the U.S. Attorney’s Office for the Southern District of New York ("USAO-SDNY") and with various states arising from the previously disclosed matter involving the dispensing of one product and U.S. Bio’s relationship with the manufacturer of that product. In accordance with the settlement agreements, the United States’ complaint against U.S. Bio was dismissed and the participating states agreed not to bring, and to dismiss with prejudice, any state law claims that they had the authority to bring against U.S. Bio. The Company paid the United States $10.7 million in fiscal 2017 and paid the participating states $2.8 million in fiscal 2018. During the year ended September 30, 2017, the Company recognized the $13.4 million settlement in Employee Severance, Litigation, and Other on the Company's Consolidated Statements of Operations. In January 2017, U.S. Bio received a subpoena for information from the USAO-EDNY relating to U.S. Bio’s activities in connection with billing for products and making returns of potential overpayments to government payers. The Company is engaged in discussions with the USAO-EDNY and has been producing documents in response to the subpoena. In November 2017, the Company’s subsidiary PharMEDium received a grand jury subpoena for documents from the U.S. Attorney's Office for the Western District of Tennessee ("USAO-WDTN") seeking various documents, including information generally related to the laboratory testing procedures of PharMEDium's products, and more specifically, for PharMEDium products packaged in a certain type of syringe at its Memphis, Tennessee facility. The Company is engaged in discussions with the USAO-WDTN and has produced documents in response to the subpoena. Opioid Lawsuits and Investigations In June 2012, the Attorney General of the State of West Virginia ("West Virginia AG") filed complaints, which were amended, in the Circuit Court of Boone County, West Virginia, against a number of pharmaceutical wholesale distributors, including the Company's subsidiary AmerisourceBergen Drug Corporation ("ABDC"), alleging, among other claims, that the distributors failed to provide effective controls and procedures to guard against diversion of controlled substances for illegitimate purposes in West Virginia, acted negligently by distributing controlled substances to pharmacies that serve individuals who abuse controlled substances, and failed to report suspicious orders of uncontrolled substances in accordance with state regulations. The West Virginia AG was seeking monetary damages and injunctive and other equitable relief. This matter was dismissed with prejudice on January 9, 2017 pursuant to a settlement agreement that provided for the payment of $16.0 million and express denial of the allegations in the complaints and any wrongdoing. During the year ended September 30, 2017, the Company recognized the $16.0 million settlement in Employee Severance, Litigation, and Other on the Company's Consolidated Statements of Operations. The Company paid the $16.0 million settlement in fiscal 2017. A significant number of counties, municipalities, and other governmental entities in a majority of U.S. states and Puerto Rico, as well as several states and tribes, have filed lawsuits in various federal, state and other courts against pharmaceutical wholesale distributors (including the Company and its subsidiary ABDC), pharmaceutical manufacturers, retail chains, medical practices, and physicians relating to the distribution of prescription opioid pain medications. Additionally, several counties and municipalities have named H.D. Smith, a subsidiary that the Company acquired in January 2018, as a defendant in such lawsuits. Other lawsuits regarding the distribution of prescription opioid pain medications have been filed by: third-party payors and similar entities; hospitals; hospital groups; and individuals, including cases styled as putative class actions. The lawsuits, which have been filed in federal, state, and other courts, generally allege violations of controlled substance laws and various other statutes as well as common law claims, including negligence, public nuisance, and unjust enrichment, and seek equitable relief and monetary damages. After a motion filed by certain plaintiffs and a hearing before the Judicial Panel on Multidistrict Litigation in November 2017, an initial group of cases was consolidated for Multidistrict Litigation ("MDL") proceedings before the United States District Court for the Northern District of Ohio. Additional cases have been, and will likely continue to be, transferred to the MDL. In April 2018, the United States, through the Department of Justice ("DOJ"), filed a motion to participate (i) in settlement discussions and (ii) as a friend of the Court by providing information to facilitate non-monetary remedies. The DOJ’s motion to participate in settlement discussions was granted on June 19, 2018. On April 11, 2018, the Court issued an order creating a litigation track, which includes dispositive motion practice, discovery, and trials in certain bellwether jurisdictions that are scheduled to commence in September 2019. Dispositive motion practice and fact discovery have commenced in certain bellwether cases. On October 5, 2018, Magistrate Judge Ruiz issued a Report & Recommendation on the first of the bellwether dispositive motions, which recommended dismissal of certain public nuisance claims but recommended that the majority of the suit be allowed to continue with discovery. The parties will file objections to the Report & Recommendation and, thereafter, Judge Polster will either adopt or modify the Report & Recommendation. Additionally, the Court has continued to oversee court-ordered settlement discussions with attorneys for the plaintiffs and certain states that it instituted at the beginning of the MDL proceedings. Aside from those parties that have already filed suit, other entities, including additional attorneys general’s offices, counties, and cities in multiple states, have indicated their intent to sue. The Company is vigorously defending itself in the pending lawsuits and intends to vigorously defend itself against any threatened lawsuits. The Company is not in a position to assess the likely outcome or its exposure, if any, with respect to these matters. In addition, on September 18, 2017, the Company received a request for documents and information on behalf of attorneys general from a coalition of states who are investigating a number of manufacturers and distributors (including ABDC) regarding the distribution of prescription opioid pain medications. The Company is engaged in discussions with the representatives of the attorneys general regarding this request and has been producing responsive documents. The Company has also received subpoenas, civil investigative demands, and other requests for information, requesting the production of documents regarding the distribution of prescription opioid pain medications from government agencies in other jurisdictions, including certain states. The Company is engaged in discussions with representatives from these government agencies regarding the requests, and has been producing responsive documents. Additionally, in fiscal 2012, ABDC received a subpoena from the U.S. Attorney's Office for the District of New Jersey ("USAO-NJ") in connection with a grand jury proceeding requesting documents concerning ABDC's program for controlling and monitoring diversion of controlled substances into channels other than for legitimate medical, scientific, and industrial purposes. ABDC also received a subpoena from the Drug Enforcement Administration ("DEA") in connection with the matter. Since fiscal 2012, ABDC has received and responded to a number of subpoenas from both the USAO-NJ and DEA requesting grand jury testimony and additional information related to electronically stored information, documents concerning specific customers' purchases of controlled substances, and DEA audits. In July 2017, the USAO-NJ and DEA served an administrative subpoena requesting documents relating to ABDC's diversion control programs from 2013 to the present. The Company is responding to the 2017 subpoena and continues to engage in dialogue with the USAO-NJ. During the fiscal year ended September 30, 2018, the Company also received administrative subpoenas from the USAO-EDNY, the U.S. Attorney's Office for the District of Colorado, the U.S. Attorney's Office for the Northern District of West Virginia, the U.S. Attorney's Office for the Western District of Michigan, and the U.S. Attorney's Office for the Middle District of Florida. Those subpoenas are substantively similar to the subpoena received from the USAO-NJ in 2017. The Company has been engaged in discussions with the various U.S. Attorney’s Offices and has been producing documents in response to the subpoenas. Since fiscal 2013, the Company has received subpoenas from the U.S. Attorney's Office for the Northern District of Ohio and ABDC has received subpoenas from the U.S. Attorney's Office for the District of Kansas in connection with grand jury proceedings requesting documents concerning ABDC's program for controlling and monitoring diversion of controlled substances into channels other than for legitimate medical, scientific, and industrial purposes. As in the USAO-NJ matter described above, in addition to requesting general information on ABDC's diversion control program, the subpoenas have also requested documents concerning specific customers' purchases of controlled substances. The Company has responded to the subpoenas and requests for information. In May 2018, the Company received a grand jury subpoena from the U.S. Attorney's Office for the Southern District of Florida. The subpoena requests documents primarily relating to certain opioid products and communications with a pharmaceutical manufacturer. The Company is in the process of responding to the subpoena. Other Contingencies New York State ("NYS") enacted the Opioid Stewardship Act ("OSA"), which went into effect on July 1, 2018. The OSA established an annual $100 million Opioid Stewardship Fund (the "Fund") and requires manufacturers, distributors, and importers licensed in NYS to ratably source the Fund. The ratable share of the assessment for each licensee is based upon opioids sold or distributed to or within NYS. The OSA requires licensees to initially report transaction data for the 2017 calendar year by August 1, 2018, which NYS will use to calculate ratable shares of the assessment. The initial payment to NYS is due on January 1, 2019 for opioids sold or distributed during calendar year 2017, and future assessments, beginning with the 2018 calendar year, will be payable quarterly beginning on April 1, 2019. The OSA expires on June 30, 2024. The Company accrued $22.0 million as an estimate of its liability under the OSA for opioids distributed from January 1, 2017 through September 30, 2018. The Company recognized this reserve in Cost of Goods Sold on its Consolidated Statement of Operations for the fiscal year ended September 30, 2018 and in Accrued Expenses and Other on its Consolidated Balance Sheet as of September 30, 2018. If other state or local jurisdictions enact similar legislation, such legislation in the aggregate may have a material adverse effect on the Company's results of operations, cash flows, or financial condition. The FDA and the Consumer Protection Branch of the Civil Division of the DOJ regulate the compounding of pharmaceutical products. The Company’s Section 503B outsourcing facilities must comply with current Good Manufacturing Practices ("GMPs") and are inspected by the FDA periodically to determine that PharMEDium is complying with such GMPs. The FDA and the DOJ have broad enforcement powers, including the ability to suspend the Company’s Section 503B outsourcing facilities from distributing pharmaceutical products. The Company continues to be in active communication with the FDA and the Consumer Protection Branch of the Civil Division of the DOJ regarding the ongoing compliance efforts of PharMEDium, including efforts to resume commercial distribution at the Memphis 503B outsourcing facility where it voluntarily suspended production activities in December 2017. Representatives of the Company and PharMEDium had an initial meeting with the FDA and the DOJ to discuss potential resolution of ongoing matters and whether a consent decree is necessary. Further discussions are anticipated, including with regard to the possible entry of a consent decree. A failure to adequately address observations identified by the FDA and the DOJ could lead to the suspension of facilities currently in operation, an enforcement action, monetary penalties and/or license revocation.

Litigation Settlements

Litigation Settlements	12 Months Ended
	Sep. 30, 2018
Litigation Settlement [Abstract]
Litigation Settlements	Litigation Settlements Antitrust Settlements Numerous class action lawsuits have been filed against certain brand pharmaceutical manufacturers alleging that the manufacturer, by itself or in concert with others, took improper actions to delay or prevent generic drugs from entering the market. The Company has not been a named a plaintiff in any of these class actions, but has been a member of the direct purchasers' class (i.e., those purchasers who purchase directly from these pharmaceutical manufacturers). None of the class actions have gone to trial, but some have settled in the past with the Company receiving proceeds from the settlement funds. During the fiscal years ended September 30, 2018 , 2017 , and 2016 , the Company recognized gains of $35.9 million , $1.4 million , and $133.8 million , respectively, relating to these class action lawsuits. These gains, which are net of attorney fees and estimated payments due to other parties, were recorded as reductions to Cost of Goods Sold in the Company's Consolidated Statements of Operations.

Business Segment Information

Business Segment Information	12 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Business Segment Information	Business Segment Information The Company is organized based upon the products and services it provides to its customers. The Company's operations are comprised of the Pharmaceutical Distribution Services reportable segment and other operating segments that are not significant enough to require separate reportable segment disclosure and, therefore, have been included in Other for the purpose of reportable segment presentation. Other consists of operating segments that focus on global commercialization services and animal health and includes ABCS, World Courier, and MWI. The chief operating decision maker ("CODM") of the Company is the Chairman, President & Chief Executive Officer of the Company, whose function is to allocate resources to, and assess the performance of, the Company's operating segments. The Pharmaceutical Distribution Services reportable segment distributes a comprehensive offering of brand-name, specialty brand-name and generic pharmaceuticals, over-the-counter healthcare products, home healthcare supplies and equipment, outsourced compounded sterile preparations, and related services to a wide variety of healthcare providers, including acute care hospitals and health systems, independent and chain retail pharmacies, mail order pharmacies, medical clinics, long-term care and alternate site pharmacies, and other customers. Through a number of operating businesses, the Pharmaceutical Distribution Services reportable segment provides pharmaceutical distribution (including plasma and other blood products, injectible pharmaceuticals, vaccines, and other specialty pharmaceutical products) and additional services to physicians who specialize in a variety of disease states, especially oncology, and to other healthcare providers, including hospitals and dialysis clinics. Additionally, the Pharmaceutical Distribution Services reportable segment provides data analytics, outcomes research, and additional services for biotechnology and pharmaceutical manufacturers. The Pharmaceutical Distribution Services reportable segment also provides pharmacy management, staffing and additional consulting services, and supply management software to a variety of retail and institutional healthcare providers. Additionally, it delivers packaging solutions to institutional and retail healthcare providers. ABCS, through a number of operating businesses, provides a full suite of integrated manufacturer services that range from clinical trial support to product post-approval and commercialization support. World Courier, which operates in over 50 countries, is a leading global specialty transportation and logistics provider for the biopharmaceutical industry. MWI is a leading animal health distribution company in the United States and in the United Kingdom. MWI sells pharmaceuticals, vaccines, parasiticides, diagnostics, micro feed ingredients, and various other products to customers in both the companion animal and production animal markets. Additionally, MWI offers demand-creating sales force services to manufacturers. The following illustrates reportable segment revenue information for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 161,699,343 $ 147,453,495 $ 141,701,997 Other 6,332,730 5,747,863 5,207,095 Intersegment eliminations (92,438 ) (57,532 ) (59,406 ) Revenue $ 167,939,635 $ 153,143,826 $ 146,849,686 Intersegment eliminations primarily represent the elimination of certain Pharmaceutical Distribution Services reportable segment sales to MWI. The following illustrates reportable segment operating income information for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 1,626,748 $ 1,643,629 $ 1,702,725 Other 355,091 373,797 327,746 Intersegment eliminations (609 ) (556 ) (103 ) Total segment operating income $ 1,981,230 $ 2,016,870 $ 2,030,368 The following reconciles total segment operating income to income before income taxes for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Total segment operating income $ 1,981,230 $ 2,016,870 $ 2,030,368 Gain from antitrust litigation settlements 35,938 1,395 133,758 LIFO (expense) credit (67,324 ) 157,782 (200,230 ) PharMEDium remediation costs (66,204 ) — — New York State Opioid Stewardship Act (22,000 ) — — Acquisition-related intangibles amortization (174,751 ) (156,378 ) (147,262 ) Warrants expense — — (140,342 ) Employee severance, litigation, and other (183,520 ) (959,327 ) (102,911 ) Pension settlement charge — — (47,607 ) Goodwill impairment (59,684 ) — — Operating income 1,443,685 1,060,342 1,525,774 Other loss (income) 25,469 (2,730 ) (5,048 ) Interest expense, net 174,699 145,185 139,912 Loss on consolidation of equity investments 42,328 — — Loss on early retirement of debt 23,766 — — Income before income taxes $ 1,177,423 $ 917,887 $ 1,390,910 Segment operating income is evaluated by the CODM of the Company and excludes gain from antitrust litigation settlements; LIFO (expense) credit; PharMEDium remediation costs; New York State Opioid Stewardship Act; acquisition-related intangibles amortization; Warrants expense; employee severance, litigation, and other; a pension settlement charge; and goodwill impairment. All corporate office expenses are allocated to each operating segment. Segment measures were adjusted in fiscal 2018 to exclude PharMEDium remediation costs, New York State Opioid Stewardship Act, and goodwill impairment as the CODM excludes these costs in the measurement of segment performance. After FDA inspections of PharMEDium's compounding facilities, the Company voluntarily suspended production activities in December 2017 at its largest compounding facility located in Memphis, Tennessee pending execution of certain remedial measures. The Company has been in active communication with the FDA and the Consumer Protection Branch of the Civil Division of the DOJ regarding its ongoing compliance efforts at PharMEDium, and representatives of the Company and PharMEDium have had an initial meeting with the DOJ and the FDA to discuss potential resolution of ongoing matters and whether a consent decree is necessary (see Item 1A. Risk Factors on page 8). Further discussions are anticipated, including with regard to the possible entry of a consent decree. The Company incurred remediation costs primarily in connection with the suspended production activities. These remediation costs are primarily classified in Cost of Goods sold in the Consolidated Statements of Operations in the fiscal year ended September 30, 2018. Future remediation costs will also include costs related to remediation activities responsive to FDA inspectional observations generally applicable to all of PharMEDium’s 503B outsourcing facilities, including product stability studies. The Company recorded a $30.0 million impairment of a non-customer note receivable related to a start-up venture in Other Loss (Income) in the Company's Consolidated Statement of Operations in the fiscal year ended September 30, 2018. The following illustrates total assets by reportable segment for the periods indicated: September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 31,892,621 $ 29,691,127 $ 28,605,047 Other 5,777,217 5,625,343 5,032,454 Total assets $ 37,669,838 $ 35,316,470 $ 33,637,501 The CODM does not review assets by operating segment for the purpose of assessing performance or allocating resources. The following illustrates depreciation and amortization by reportable segment for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 225,608 $ 188,065 $ 170,973 Other 64,768 53,160 46,500 Acquisition-related intangibles amortization 174,751 156,378 147,262 Total depreciation and amortization $ 465,127 $ 397,603 $ 364,735 Depreciation and amortization includes depreciation and amortization of property and equipment and intangible assets, but excludes amortization of deferred financing costs and other debt-related items, which are included in interest expense. The following illustrates capital expenditures by reportable segment for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 190,191 $ 339,478 $ 359,391 Other 146,220 126,919 105,225 Total capital expenditures $ 336,411 $ 466,397 $ 464,616

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments The recorded amounts of the Company's cash and cash equivalents, accounts receivable, and accounts payable as of September 30, 2018 and 2017 approximate fair value based upon the relatively short-term nature of these financial instruments. Within Cash and Cash Equivalents, the Company had $1,050.0 million and $800.0 million of investments in money market accounts as of September 30, 2018 and 2017 . The fair value of the money market accounts was determined based upon unadjusted quoted prices in active markets for identical assets, otherwise known as Level 1 inputs. The recorded amount of long-term debt (see Note 6 ) and the corresponding fair value as of September 30, 2018 were $4,158.5 million and $4,000.1 million , respectively. The recorded amount of long-term debt and the corresponding fair value as of September 30, 2017 were $3,429.9 million and $3,522.5 million , respectively. The fair value of long-term debt was determined based upon inputs other than quoted prices, otherwise known as Level 2 inputs.

Quarterly Financial Information

Quarterly Financial Information (Unaudited)	12 Months Ended
	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (Unaudited)	Quarterly Financial Information (Unaudited) Fiscal Year Ended September 30, 2018 (in thousands, except per share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter Fiscal Year Revenue $ 40,466,332 $ 41,033,858 $ 43,142,309 $ 43,297,136 $ 167,939,635 Gross profit (a) $ 1,112,652 $ 1,255,683 $ 1,211,341 $ 1,032,641 $ 4,612,317 Distribution, selling, and administrative expenses; depreciation; and amortization 663,658 736,814 746,593 778,363 2,925,428 Employee severance, litigation, and other 30,021 37,449 75,553 40,497 183,520 Goodwill impairment — — — 59,684 59,684 Operating income $ 418,973 $ 481,420 $ 389,195 $ 154,097 $ 1,443,685 Net income (b) $ 861,853 $ 282,160 $ 277,875 $ 194,004 $ 1,615,892 Net income attributable to AmerisourceBergen Corporation (b) $ 861,853 $ 287,455 $ 275,809 $ 233,288 $ 1,658,405 Earnings per share operations: Basic $ 3.95 $ 1.31 $ 1.26 $ 1.08 $ 7.61 Diluted $ 3.90 $ 1.29 $ 1.25 $ 1.07 $ 7.53 __________________________________________________________ (a) The second and third quarters of the fiscal year ended September 30, 2018 include gains from antitrust litigation settlements of $0.3 million and $35.6 million . The third quarter of the fiscal year ended September 30, 2018 includes a LIFO credit of $16.1 million . The fourth quarter of the fiscal year ended September 30, 2018 includes LIFO expense of $83.5 million . The second, third, and fourth quarters of the fiscal year ended September 30, 2018 include PharMEDium remediation costs of $22.5 million , $12.0 million , and $26.6 million . The fourth quarter of the fiscal year ended September 30, 2018 includes a $22.0 million estimate of our liability under the New York State Opioid Stewardship Act. (b) The first quarter of the fiscal year ended September 30, 2018 includes a loss on early retirement of debt of $23.8 million . The second quarter of the fiscal year ended September 30, 2018 includes a $42.3 million loss on consolidation of equity investments and a $30.0 million impairment of a non-customer note receivable. The first and fourth quarters of the fiscal year ended September 30, 2018 included discrete income tax benefits recognized in connection with the 2017 Tax Act of $587.6 million and $25.0 million , respectively. Fiscal Year Ended September 30, 2017 (in thousands, except per share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter Fiscal Year Revenue $ 38,169,265 $ 37,147,402 $ 38,707,144 $ 39,120,015 $ 153,143,826 Gross profit (a) $ 1,037,680 $ 1,256,427 $ 1,079,875 $ 1,172,020 $ 4,546,002 Distribution, selling, and administrative expenses; depreciation; and amortization 616,627 619,512 624,982 665,212 2,526,333 Employee severance, litigation, and other (b) 21,066 11,934 284,517 641,810 959,327 Operating income (loss) $ 399,987 $ 624,981 $ 170,376 $ (135,002 ) $ 1,060,342 Net income (loss) $ 247,246 $ 411,473 $ 50,352 $ (344,587 ) $ 364,484 Earnings per share operations: Basic $ 1.13 $ 1.89 $ 0.23 $ (1.58 ) $ 1.67 Diluted $ 1.11 $ 1.86 $ 0.23 $ (1.58 ) $ 1.64 __________________________________________________________ (a) The first quarter of the fiscal year ended September 30, 2017 includes gains from antitrust and litigation settlements of $1.4 million . The first quarter of the fiscal year ended September 30, 2017 includes LIFO expense of $28.3 million . The second, third, and fourth quarters of the fiscal year ended September 30, 2017 include LIFO credits of $86.5 million , $24.7 million , and $74.9 million , respectively. (b) The third quarter of the fiscal year ended September 30, 2017 includes $273.4 million for litigation settlements. The fourth quarter of the fiscal year ended September 30, 2017 includes a $625.0 million litigation accrual.

Subsequent Event

Subsequent Event	12 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event In November 2018, the Company's board of directors increased the quarterly dividend paid on common stock by 5% and declared a regular quarterly cash dividend of $0.40 per share, payable on December 3, 2018 to shareholders of record on November 19, 2018.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Sep. 30, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS (In thousands) Balance at Beginning of Period Charged to Costs and Expenses (1) Deductions- Describe (2) Balance at End of Period (3) Year Ended September 30, 2018 Allowances for returns and doubtful accounts $ 1,068,251 $ 3,397,562 $ (3,415,912 ) $ 1,049,901 Year Ended September 30, 2017 Allowances for returns and doubtful accounts $ 926,034 $ 3,157,960 $ (3,015,743 ) $ 1,068,251 Year Ended September 30, 2016 Allowances for returns and doubtful accounts $ 923,755 $ 2,882,914 $ (2,880,635 ) $ 926,034 __________________________________________________________ (1) Represents the provision for returns and doubtful accounts. (2) Represents reductions to the returns allowance and accounts receivable written off during year, net of recoveries. (3) Includes an allowance for doubtful accounts for long-term accounts receivable within Other Assets on the Consolidated Balance Sheets of $13,568 thousand , $17,890 thousand and $20,689 thousand as of September 30, 2018 , 2017 , and 2016 , respectively.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Consolidation	The accompanying financial statements present the consolidated financial position, results of operations, and cash flows of the Company as of the dates and for the periods indicated. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	The preparation of financial statements in conformity with U.S. generally accepted accounting principles ("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 due to uncertainties inherent in such estimates. Management periodically evaluates estimates used in the preparation of the financial statements for continued reasonableness.
Reclassifications	Certain reclassifications have been made to prior-period amounts in order to conform to the current year presentation.
New Accounting Pronouncements	Recently Adopted Accounting Pronouncements In March 2016, the FASB issued ASU No. 2016-09, "Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting" ("ASU 2016-09"). ASU 2016-09 requires all income tax effects of awards to be recognized in the income statement when the awards vest or are exercised. It also allows an employer to repurchase more of an employee's shares for tax withholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur. ASU 2016-09 was effective for annual reporting periods beginning after December 15, 2016 and interim periods within those fiscal years. During the quarter ended December 31, 2016, the Company early adopted ASU 2016-09, which resulted in a cumulative adjustment to retained earnings and the establishment of a deferred tax asset as of October 1, 2016 of $47.1 million for previously unrecognized tax benefits. The Company elected to adopt the Statement of Cash Flows presentation of the excess tax benefits prospectively. 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 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. The Company completed its evaluation of the impact of adopting ASU 2016-08, ASU 2016-10, and ASU 2014-09, collectively Accounting Standards Codification 606 or "ASC 606". The Company adopted ASC 606 as of October 1, 2018 on a modified retrospective basis. 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. 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 continues to evaluate the impact of adopting this new accounting guidance and, therefore, cannot reasonably estimate the impact on the results of operations or cash flows at this time. The Company expects to adopt this standard in the first quarter of fiscal 2020. As of September 30, 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.
Business Combinations	The assets acquired and liabilities assumed from the acquired business are recorded at fair value, with the residual of the purchase price recorded as goodwill. The results of operations of the acquired businesses are included in the Company's operating results from the dates of acquisition.
Cash Equivalents	The Company considers all highly liquid investments with original maturities of three months or less to be cash equivalents. The carrying value of cash equivalents approximates fair value.
Concentrations of Credit Risk and Allowance for Doubtful Accounts	The Company sells its merchandise inventories to a large number of customers in the healthcare industry that include institutional and retail healthcare providers. Institutional healthcare providers include acute care hospitals, health systems, mail order pharmacies, long-term care and other alternate care pharmacies and providers of pharmacy services to such facilities, and physician offices. Retail healthcare providers include national and regional retail drugstore chains, independent community pharmacies, pharmacy departments of supermarkets and mass merchandisers, and veterinarians. The financial condition of the Company's customers can be affected by changes in government reimbursement policies as well as by other economic pressures in the healthcare industry. The Company's trade accounts receivables are exposed to credit risk. Revenue from the various agreements and arrangements with the Company's largest customer in the fiscal year ended September 30, 2018 , Walgreens Boots Alliance, Inc. ("WBA"), accounted for approximately 33% of revenue and represented approximately 49% of accounts receivable, net of incentives, as of September 30, 2018 . Express Scripts, Inc., the Company's second largest customer in the fiscal year ended September 30, 2018 , accounted for approximately 13% of revenue and represented approximately 8% of accounts receivable, net as of September 30, 2018 . The Company generally does not require collateral for trade receivables. In determining the appropriate allowance for doubtful accounts, the Company considers a combination of factors, such as the aging of trade receivables, industry trends, and its customers' financial strength, credit standing, and payment and default history. Changes in these factors, among others, may lead to adjustments in the Company's allowance for doubtful accounts. The calculation of the required allowance requires judgment by Company management as to the impact of those and other factors on the ultimate realization of its trade receivables. Each of the Company's business units performs ongoing credit evaluations of its customers' financial condition and maintains reserves for probable bad debt losses based upon historical experience and for specific credit problems when they arise. There were no significant changes to this process during the fiscal years ended September 30, 2018 , 2017 , and 2016 , and bad debt expense was computed in a consistent manner during these periods. The Company maintains cash and cash equivalents with several financial institutions. Deposits held with banks may exceed the amount of insurance provided on such deposits. These deposits may be redeemed upon demand and are maintained with financial institutions with reputable credit and, therefore, bear minimal credit risk. The Company seeks to mitigate such risks by monitoring the risk profiles of these counterparties. The Company also seeks to mitigate risk by monitoring the investment strategy of money market accounts in which it is invested, which are classified as cash equivalents.
Contingencies	Loss Contingencies: In the ordinary course of its business, the Company becomes involved in lawsuits, administrative proceedings, government subpoenas, government investigations, and other disputes, including antitrust, commercial, environmental, product liability, intellectual property, regulatory, employment discrimination, and other matters. Significant damages or penalties may be sought from the Company in some matters, and some matters may require years for the Company to resolve. The Company records a liability when it is probable that a loss has been incurred and the amount is reasonably estimable. The Company also performs an assessment of the materiality of loss contingencies where a loss is either not probable or it is reasonably possible that a loss could be incurred in excess of amounts accrued. If a loss or an additional loss has at least a reasonable possibility of occurring and the impact on the financial statements would be material, the Company provides disclosure of the loss contingency in the notes to its financial statements. The Company reviews all contingencies at least quarterly to determine whether the likelihood of loss has changed and to assess whether a reasonable estimate of the loss or the range of the loss can be made (see Note 13 ). Gain Contingencies: The Company records gain contingencies when they are realized. Gains from antitrust litigation settlements are realized upon the receipt of cash and recorded as a reduction to cost of goods sold because they represent a recovery of amounts historically paid to manufacturers to originally acquire the pharmaceuticals that were the subject of the antitrust litigation settlements (see Note 14 ).
Derivative Financial Instruments	The Company records all derivative financial instruments on the balance sheet at fair value and complies with established criteria for designation and effectiveness of hedging relationships. The Company's policy prohibits it from entering into derivative financial instruments for speculative or trading purposes.
Foreign Currency	When the functional currency of the Company's foreign operations is the applicable local currency, assets and liabilities are translated into U.S. dollars using the current exchange rates in effect at the balance sheet date, while revenues and expenses are translated at the weighted average exchange rates for the period. The resulting translation adjustments are recorded as a component of Accumulated Other Comprehensive Loss within Stockholders' Equity.
Goodwill and Other Intangible Assets	Goodwill and other intangible assets with indefinite lives, such as certain trademarks and trade names, are not amortized; rather, they are tested for impairment at least annually. For the purpose of these impairment tests, we can elect to perform a qualitative assessment to determine if it is more likely than not that the fair values of its reporting units and indefinite-lived intangible assets are less than the respective carrying values of those reporting units and indefinite-lived intangible assets, respectively. The Company elected to bypass performing the qualitative assessment and, in the fourth quarter of fiscal 2018, went directly to performing our annual quantitative assessments of the goodwill and indefinite-lived intangible assets for the current year. The Company may elect to perform the qualitative annual assessment in future periods. The goodwill impairment test requires us to compare the carrying value of the reporting unit's net assets to the fair value of the reporting unit. If the fair value exceeds the carrying value, no further evaluation is required, and no impairment loss is recognized. If the carrying amount exceeds the fair value, the difference between the carrying value and the fair value is recorded as an impairment loss, the amount of which may not exceed the total amount of goodwill allocated to the reporting unit. Goodwill arises from acquisitions or consolidations of specific operating companies and is assigned to the reporting unit in which a particular operating company resides. The Company identifies its reporting units based upon the Company's management reporting structure, beginning with its operating segments. The Company evaluates whether the components within its operating segments have similar economic characteristics, which include the nature of the components' products, services, and production processes, the types of customers and the methods by which products or services are delivered to customers, and the components' regulatory environment. The Company's reporting units include Pharmaceutical Distribution Services, Profarma Distribuidora de Produtos Farmacêuticos S.A. ("Profarma"), AmerisourceBergen Consulting Services ("ABCS"), World Courier, and MWI Animal Health ("MWI"). The Company utilizes an income-based approach to value its reporting units, with the exception of the Profarma reporting unit, the fair value of which is based upon its publicly-traded stock price, plus an estimated control premium. The income-based approach relies on a discounted cash flow analysis, which considers forecasted cash flows discounted at an appropriate discount rate, to determine the fair value of each reporting unit. The Company generally believes that market participants would use a discounted cash flow analysis to determine the fair value of the Company's reporting units in a sale transaction. The annual goodwill impairment test requires the Company to make a number of assumptions and estimates concerning future levels of revenue growth, operating margins, depreciation, amortization, capital expenditures, and working capital requirements, which are based upon the Company's long-range plan. The discount rate is an estimate of the overall after-tax rate of return required by a market participant whose weighted average cost of capital includes both debt and equity, including a risk premium. While the Company uses the best available information to prepare its cash flows and discount rate assumptions, actual future cash flows and/or market conditions could differ significantly resulting in future impairment charges related to recorded goodwill balances. While there are always changes in assumptions to reflect changing business and market conditions, the Company's overall methodology and the population of assumptions used have remained unchanged. The impairment test for indefinite-lived intangibles other than goodwill (certain trademarks and trade names) consists of a comparison of the fair value of the indefinite-lived intangible asset to the carrying value of the asset as of the impairment testing date. The Company estimates the fair value of its indefinite-lived intangibles using the relief from royalty method. The Company believes the relief from royalty method is a widely used valuation technique for such assets. The fair value derived from the relief from royalty method is measured as the discounted cash flow savings realized from owning such indefinite-lived trademarks and trade names and not having to pay a royalty for their use. The Company completed its required annual impairment tests relating to goodwill and indefinite-lived intangible assets in the fourth quarter of the fiscal years ended September 30, 2018 , 2017 , and 2016 . The Company recorded a goodwill impairment of $59.7 million in its Profarma reporting unit in connection with its fiscal 2018 annual impairment test (see Note 5). No goodwill impairments were recorded in the fiscal years ended September 30, 2017 and 2016. No indefinite-lived intangible asset impairments were recorded in the fiscal years ended September 30, 2018, 2017, and 2016. In connection with the goodwill impairment recorded in the Profarma reporting unit, the Company first performed a recoverability assessment of Profarma's long-lived assets by comparing its undiscounted cash flows to the carrying value of the asset group, and it was determined to be recoverable; however, the forecasted undiscounted cash flows used to perform the recoverability assessment are inherently uncertain and include assumptions that could differ from actual results in future periods. Finite-lived intangible assets are amortized using the straight-line method over the estimated useful lives of the assets. The Company performs a recoverability assessment of its long-lived assets when impairment indicators are present. PharMEDium Healthcare Holdings, Inc.'s ("PharMEDium") long-lived assets were also tested for recoverability in fiscal 2018 due to the existence of an impairment indicator. The Company voluntarily suspended production activities in December 2017 at its largest compounding facility located in Memphis, Tennessee after U.S. Food and Drug Administration ("FDA") inspections of PharMEDium's compounding facilities. The Company concluded that the suspension of production activity represented an impairment indicator of PharMEDium's long-lived assets and, therefore, performed a recoverability assessment of PharMEDium's long-lived assets. The recoverability assessment was based on the carrying value of the PharMEDium asset group, excluding goodwill. The carrying value of the asset group was $903 million as of September 30, 2018. The Company concluded that PharMEDium's long-lived assets are recoverable as of September 30, 2018; however, the forecasted undiscounted cash flows used to perform the recoverability assessment are inherently uncertain and include assumptions, such as the timing of resumed production activities and profitability, that could differ from actual results in future periods.
Income Taxes	The Company accounts for income taxes using a method that requires recognition of deferred tax assets and liabilities for expected future tax consequences of temporary differences that currently exist between tax bases and financial reporting bases of the Company's assets and liabilities (commonly known as the asset and liability method). In assessing the need to establish a valuation allowance on deferred tax assets, the Company considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained upon examination by the taxing authorities, including resolutions of any related appeals or litigation processes, based upon the technical merits of the position. Tax benefits associated with uncertain tax positions that have met the recognition criteria are measured and recorded based upon the highest probable outcome that is more than 50% likely to be realized after full disclosure and resolution of a tax examination.
Investment Securities Available-For-Sale	The Company's marketable debt securities have been classified and accounted for as available-for-sale. Management determines the appropriate classification of its investments at the time of purchase and evaluates the classifications at each balance sheet date. The Company classifies its marketable debt securities as either short-term or long-term based upon each instrument's underlying contractual maturity date. Marketable debt securities with maturities of 12 months or less are classified as short-term and marketable debt securities with maturities greater than 12 months are classified as long-term. The Company's marketable debt securities are carried at fair value, with unrealized gains and losses reported as a component of Accumulated Other Comprehensive Loss in Stockholders' Equity, with the exception of unrealized losses believed to be other-than-temporary, which are reported in earnings in the current period. The cost of securities sold is based upon the specific identification method.
Equity Method Investments	The Company first evaluates its investments in accordance with the variable interest model to determine whether it has a controlling financial interest in an investment. This evaluation is made as of the date on which the Company makes its initial investment, and subsequent evaluations are made if the structure of the investment changes. If it has determined that an investment is a variable interest entity ("VIE"), the Company evaluates whether the VIE is required to be consolidated. When the Company holds rights that give it the power to direct the activities of an entity that most significantly impact the entity's economic performance, combined with the obligation to absorb an entity's losses and the right to receive benefits, the Company consolidates a VIE. If it is determined that an investment is not a VIE, the Company then evaluates its investments under the voting interest model and generally consolidates investments in which it holds an ownership interest of greater than 50%. When the Company consolidates less than wholly-owned subsidiaries, it discloses its noncontrolling interest in its consolidated financial statements. The Company uses the equity method of accounting for its investments in entities in which it has significant influence; generally, this represents an ownership interest of between 20% and 50%. A decline in value that is determined to be other-than-temporary is recorded as an impairment charge as a component of earnings in the period in which that determination is made.
Leases	The Company is often involved in the construction of its distribution facilities. In certain cases, the Company makes payments for certain structural components included in the lessor's construction of the leased assets, which result in the Company being deemed the owner of the leased assets for accounting purposes. As a result, regardless of the significance of the payments, Accounting Standards Codification 840, Leases, ("ASC 840") defines those payments as automatic indicators of ownership and requires the Company to capitalize the lessor's total project cost with a corresponding financing obligation. Upon completion of the lessor's project, the Company performs a sale-leaseback analysis pursuant to ASC 840 to determine if these assets and the related financing obligations can be derecognized from the Company's Consolidated Balance Sheet. If the Company is deemed to have "continuing involvement," the leased assets and the related financing obligations remain on the Company's Consolidated Balance Sheet and are amortized over the life of the assets and the lease term, respectively. All other leases are considered operating leases in accordance with ASC 840. Assets subject to an operating lease and the related lease payments are not recorded on the Company's Consolidated Balance Sheet. Rent expense is recognized on a straight-line basis over the expected lease term and is recorded in Distribution, Selling, and Administrative in the Company's Consolidated Statements of Operations.
Manufacturer Incentives	The Company considers fees and other incentives received from its suppliers relating to the purchase or distribution of inventory to represent product discounts, and, as a result, they are recognized within cost of goods sold upon the sale of the related inventory.
Merchandise Inventories	Inventories are stated at the lower of cost or market. Cost for approximately 75% and 80% of the Company's inventories as of September 30, 2018 and 2017 , respectively, has been determined using the last-in, first-out ("LIFO") method. If the Company had used the first-in, first-out method of inventory valuation, which approximates current replacement cost, inventories would have been approximately $1,534.4 million and $1,467.0 million higher than the amounts reported as of September 30, 2018 and 2017 , respectively. The Company recorded LIFO expense of $67.3 million and $200.2 million in the fiscal years ended September 30, 2018 and 2016, respectively, and a LIFO credit of $157.8 million in the fiscal year ended September 30, 2017 . The annual LIFO provision is affected by changes in inventory quantities, product mix, and manufacturer pricing practices, which may be impacted by market and other external influences, many of which are difficult to predict. Changes to any of the above factors can have a material impact to the Company's annual LIFO provision.
Property and Equipment	Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, which range from 3 to 40 years for buildings and improvements and from 3 to 10 years for machinery, equipment, and other. The costs of repairs and maintenance are charged to expense as incurred. The Company capitalizes project costs relating to computer software developed or obtained for internal use when the activities related to the project reach the application development stage. Costs that are associated with preliminary stage activities, training, maintenance, and all other post-implementation stage activities are expensed as they are incurred. Software development costs are depreciated using the straight-line method over the estimated useful lives, which range from 3 to 10 years.
Revenue Recognition	The Company recognizes revenue when persuasive evidence of an arrangement exists, products have been delivered or services have been rendered, the price is fixed or determinable, and collectability is reasonably assured. Revenue, as reflected in the accompanying Consolidated Statements of Operations, is net of estimated sales returns and allowances, and other customer incentives. 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. As of September 30, 2018 and 2017 , the Company's accrual for estimated customer sales returns was $988.8 million and $1,001.7 million , respectively. The Company reports the gross dollar amount of bulk deliveries to customer warehouses in revenue and the related costs in cost of goods sold. Bulk delivery transactions are arranged by the Company at the express direction of the customer, and involve either drop shipments from the supplier directly to customers' warehouse sites or cross-dock shipments from the supplier to the Company for immediate shipment to the customers' warehouse sites. The Company is a principal to these transactions because it is the primary obligor and has the ultimate and contractual responsibility for fulfillment and acceptability of the products purchased, and it bears full risk of delivery and loss for products, whether the products are drop-shipped or shipped via cross-dock. The Company also bears full credit risk associated with the creditworthiness of any bulk delivery customer. As a result, the Company records bulk deliveries to customer warehouses as gross revenues. Gross profit earned by the Company on bulk deliveries was not material in any year presented.
Share-Based Compensation	The Company accounts for the compensation cost of all share-based payments at fair value. The Company estimates the fair value of option grants using a binomial option pricing model. The fair value of restricted stock units and performance stock units is based upon the grant date market price of the Company’s common stock. Share-based compensation expense is recognized over the requisite service period within Distribution, Selling, and Administrative in the Consolidated Statements of Operations to correspond with the same line item as the cash compensation paid to employees. Compensation expense associated with nonvested performance stock units is dependent upon the Company's periodic assessment of the probability of the targets being achieved and its estimate of the number of shares that will ultimately be issued. The income tax effects of awards is recognized when the awards vest or are settled and are recognized in Income Tax Expense in the Company’s Consolidated Statements of Operations and in cash flows from operations in the Consolidated Statements of Cash Flows. Prior to fiscal 2017, tax benefits from share-based compensation were recorded as adjustments to Additional Paid-in Capital within Stockholders’ Equity and as cash flows from financing activities within the Statement of Cash Flows (see Recently Adopted Accounting Pronouncements).
Shipping and Handling Costs	Shipping and handling costs include all costs to warehouse, pick, pack, and deliver inventory to customers.
Supplier Reserves	The Company establishes reserves against amounts due from its suppliers relating to various price and rebate incentives, including deductions or billings taken against payments otherwise due to them from the Company. These reserve estimates are established based upon the judgment of Company management after carefully considering the status of current outstanding claims, historical experience with the suppliers, the specific incentive programs, and any other pertinent information available to the Company. The Company evaluates the amounts due from its suppliers on a continual basis and adjusts the reserve estimates when appropriate based upon changes in factual circumstances. The ultimate outcome of any outstanding claim may be different than the Company's estimate.
Warrants	The Company accounted for the warrants issued to subsidiaries of WBA (collectively, the "Warrants") in accordance with the guidance for equity-based payments to non-employees. Using a binomial lattice model approach, the fair value of the Warrants was initially measured at the date of issuance, and the related expenses were recognized over the vesting period as an operating expense. The fair value of the Warrants was remeasured at the end of each reporting period, and an adjustment was recorded in the statement of operations to record the impact as if the newly measured fair value of the awards had been used in recognizing expense starting when the awards were originally issued and through the remeasurement date. In the fiscal year ended September 30, 2016, the Warrants were exercised by WBA in full (see Note 7 ).

Variable Interest Entity (Table

Variable Interest Entity (Tables)	12 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Variable Interest Entities	The following assets and liabilities of Profarma are included in the Company's Consolidated Balance Sheet: (in thousands) September 30, Cash and cash equivalents $ 26,801 Accounts receivables, net 144,646 Merchandise inventories 168,931 Prepaid expenses and other 61,924 Property and equipment, net 32,667 Goodwill 82,309 Other intangible assets 80,974 Other long-term assets 8,912 Total assets $ 607,164 Accounts payable $ 150,102 Accrued expenses and other 37,195 Short-term debt 115,461 Long-term debt 39,704 Deferred income taxes 46,137 Other long-term liabilities 31,988 Total liabilities $ 420,587

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Domestic and foreign income from continuing operations before income taxes	The following illustrates domestic and foreign income before income taxes for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Domestic $ 704,935 $ 394,721 $ 906,415 Foreign 472,488 523,166 484,495 Total $ 1,177,423 $ 917,887 $ 1,390,910
Income tax provision	The income tax (benefit) provision for the periods indicated is as follows: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Current provision: Federal $ 247,755 $ 141,071 $ 11,892 State and local 39,328 35,950 26,741 Foreign 69,972 57,313 55,275 Total current provision 357,055 234,334 93,908 Deferred (benefit) provision: Federal (828,023 ) 265,074 (119,218 ) State and local 33,887 54,995 (11,490 ) Foreign (1,388 ) (1,000 ) (219 ) Total deferred (benefit) provision (795,524 ) 319,069 (130,927 ) (Benefit) provision for income taxes $ (438,469 ) $ 553,403 $ (37,019 )
Reconciliation of the effective income tax rate	A reconciliation of the statutory U.S. federal income tax rate to the effective income tax rate for the periods indicated is as follows: Fiscal Year Ended September 30, 2018 2017 2016 Statutory U.S. federal income tax rate 24.5% 35.0% 35.0% State and local income tax rate, net of federal tax benefit (0.1) 5.4 0.6 Foreign (6.2) (14.6) (8.4) Warrants — — (32.8) Valuation allowance (1.4) 2.2 2.2 Excess tax benefits related to share-based compensation (1.8) (3.8) — Litigation settlements and accruals (see Note 13) (6.3) 34.3 — Goodwill impairment (see Note 5) 1.7 — — Tax reform (52.0) — — Capital gain on distribution 3.6 — — Other 0.8 1.8 0.7 Effective income tax rate (37.2)% 60.3% (2.7)%
Significant components of deferred tax liabilities (assets)	Significant components of the Company's deferred tax liabilities (assets) are as follows: September 30, (in thousands) 2018 2017 Merchandise inventories $ 1,189,801 $ 1,519,779 Property and equipment 133,417 150,240 Goodwill and other intangible assets 853,747 1,214,597 Other 747 1,126 Gross deferred tax liabilities 2,177,712 2,885,742 Net operating loss and tax credit carryforwards (421,808 ) (320,180 ) Capital loss carryforwards — (64,346 ) Allowance for doubtful accounts (20,126 ) (25,871 ) Accrued expenses (17,363 ) (36,188 ) Employee and retiree benefits (10,210 ) (17,121 ) Share-based compensation (28,888 ) (59,495 ) Other (49,892 ) (81,009 ) Gross deferred tax assets (548,287 ) (604,210 ) Valuation allowance for deferred tax assets 199,985 211,080 Deferred tax assets, net of valuation allowance (348,302 ) (393,130 ) Net deferred tax liabilities $ 1,829,410 $ 2,492,612
Reconciliation of the beginning and ending amount of unrecognized tax benefits, excluding interest and penalties	A reconciliation of the beginning and ending amount of unrecognized tax benefits, excluding interest and penalties, for the periods indicated is as follows: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Unrecognized tax benefits at beginning of period $ 323,869 $ 75,766 $ 44,722 Additions of tax positions of the current year 2,804 252,866 24,145 Additions to tax positions of the prior years 558 1,049 11,840 Reductions of tax positions of the prior years (224,878 ) (668 ) (1,407 ) Settlements with taxing authorities (1,847 ) (3,285 ) (2,589 ) Expiration of statutes of limitations (2,382 ) (1,859 ) (945 ) Unrecognized tax benefits at end of period $ 98,124 $ 323,869 $ 75,766

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the carrying value of goodwill	The following is a summary of the changes in the carrying value of goodwill, by reportable segment, for the fiscal years ended September 30, 2018 and 2017 : (in thousands) Pharmaceutical Distribution Services Other Total Goodwill as of September 30, 2016 $ 4,270,550 $ 1,720,947 $ 5,991,497 Goodwill recognized in connection with acquisitions — 54,151 54,151 Goodwill disposed in connection with divestiture — (3,564 ) (3,564 ) Foreign currency translation — 2,197 2,197 Goodwill as of September 30, 2017 4,270,550 1,773,731 6,044,281 Goodwill recognized in connection with acquisitions 641,909 39,352 681,261 Goodwill impairment (59,684 ) — (59,684 ) Foreign currency translation — (1,586 ) (1,586 ) Goodwill as of September 30, 2018 $ 4,852,775 $ 1,811,497 $ 6,664,272
Other intangible assets - indefinite-lived	The following is a summary of other intangible assets: September 30, 2018 September 30, 2017 (dollars in thousands) Weighted Average Remaining Useful Life Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Indefinite-lived trade names $ 685,380 $ — $ 685,380 $ 685,088 $ — $ 685,088 Finite-lived: Customer relationships 14 years 2,549,245 (555,440 ) 1,993,805 2,329,665 (408,636 ) 1,921,029 Trade names and other 13 years 397,946 (129,303 ) 268,643 325,353 (98,189 ) 227,164 Total other intangible assets $ 3,632,571 $ (684,743 ) $ 2,947,828 $ 3,340,106 $ (506,825 ) $ 2,833,281
Other intangible assets - finite-lived	The following is a summary of other intangible assets: September 30, 2018 September 30, 2017 (dollars in thousands) Weighted Average Remaining Useful Life Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Indefinite-lived trade names $ 685,380 $ — $ 685,380 $ 685,088 $ — $ 685,088 Finite-lived: Customer relationships 14 years 2,549,245 (555,440 ) 1,993,805 2,329,665 (408,636 ) 1,921,029 Trade names and other 13 years 397,946 (129,303 ) 268,643 325,353 (98,189 ) 227,164 Total other intangible assets $ 3,632,571 $ (684,743 ) $ 2,947,828 $ 3,340,106 $ (506,825 ) $ 2,833,281

Debt (Tables)

Debt (Tables)	12 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt Instruments	Debt consisted of the following: September 30, (in thousands) 2018 2017 Revolving credit note $ — $ — Receivables securitization facility due 2019 500,000 500,000 Term loans due 2020 398,665 547,860 Multi-currency revolving credit facility due 2021 — — Overdraft facility due 2021 (£30,000) 13,269 12,121 $400,000, 4.875% senior notes due 2019 — 398,399 $500,000, 3.50% senior notes due 2021 498,392 497,877 $500,000, 3.40% senior notes due 2024 497,255 496,766 $500,000, 3.25% senior notes due 2025 495,632 494,950 $750,000, 3.45% senior notes due 2027 742,258 — $500,000, 4.25% senior notes due 2045 494,298 494,082 $500,000, 4.30% senior notes due 2047 492,222 — Capital lease obligations 745 — Nonrecourse debt 177,453 — Total debt 4,310,189 3,442,055 Less AmerisourceBergen Corporation current portion 13,976 12,121 Less nonrecourse current portion 137,681 — Total, net of current portion $ 4,158,532 $ 3,429,934

Stockholders' Equity and Weig_2

Stockholders' Equity and Weighted Average Common Shares Outstanding (Tables)	12 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Components of accumulated other comprehensive loss	The following illustrates the components of Accumulated Other Comprehensive Loss, net of income taxes: September 30, (in thousands) 2018 2017 Pension and postretirement adjustments $ (5,065 ) $ (4,186 ) Foreign currency translation (74,811 ) (92,164 ) Other 623 500 Total accumulated other comprehensive loss $ (79,253 ) $ (95,850 )
Components of diluted weighted average shares outstanding	The following illustrates the components of diluted weighted average shares outstanding: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Weighted average common shares outstanding - basic 217,872 218,375 212,206 Effect of dilutive securities - stock options, restricted stock, restricted stock units, and the unsettled ASR transaction 2,464 3,227 3,338 Dilutive effect of the Warrants — — 10,415 Weighted average common shares outstanding - diluted 220,336 221,602 225,959

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Weighted average assumptions	The following weighted average assumptions were used to estimate the fair values of options granted: Fiscal Year Ended September 30, 2018 2017 2016 Risk-free interest rate 1.89% 1.26% 1.40% Expected dividend yield 1.96% 1.80% 1.38% Volatility of common stock 26.54% 26.78% 25.05% Expected life of the options 3.76 years 3.74 years 3.72 years
Stock options	A summary of the Company's stock option activity and related information for its option plans for the fiscal year ended September 30, 2018 is presented below: (in thousands, except exercise price and contractual term) Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value Outstanding as of September 30, 2017 10,287 $70 4 years $ 170,856 Granted 1,538 $78 Exercised (2,742 ) $51 Forfeited (604 ) $84 Expired (58 ) $95 Outstanding as of September 30, 2018 8,421 $77 4 years $ 142,557 Exercisable as of September 30, 2018 4,561 $72 3 years $ 98,863 Expected to vest after September 30, 2018 3,732 $82 5 years $ 41,982
Nonvested options	A summary of the status of the Company's nonvested options as of September 30, 2018 and changes during the fiscal year ended September 30, 2018 is presented below: (in thousands, except grant date fair value) Options Weighted Average Grant Date Fair Value Nonvested as of September 30, 2017 4,752 $15 Granted 1,538 $14 Vested (1,826 ) $14 Forfeited (604 ) $15 Nonvested as of September 30, 2018 3,860 $15
Nonvested restricted shares	A summary of the status of the Company's nonvested restricted stock units as of September 30, 2018 and changes during the fiscal year ended September 30, 2018 are presented below: (in thousands, except grant date fair value) Restricted Stock Units Weighted Average Grant Date Fair Value Nonvested as of September 30, 2017 819 $84 Granted 526 $78 Vested (173 ) $91 Forfeited (149 ) $81 Nonvested as of September 30, 2018 1,023 $80
Nonvested performance stock units	A summary of the status of the Company's nonvested performance stock units as of September 30, 2018 and changes during the fiscal year ended September 30, 2018 is presented below (based upon target award amounts). (in thousands, except grant date fair value) Performance Stock Units Weighted Average Grant Date Fair Value Nonvested as of September 30, 2017 201 $85 Granted 150 $78 Vested (80 ) $98 Forfeited (27 ) $79 Nonvested as of September 30, 2018 244 $77

Leases and Other Commitments (T

Leases and Other Commitments (Tables)	12 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Future minimum lease payments, operating leases	As of September 30, 2018 , future minimum rental payments under noncancelable operating leases and financing obligations were as follows: Payments Due by Fiscal Year (in thousands) Operating Leases Financing Obligations 1 Total 2019 $ 89,589 $ 26,561 $ 116,150 2020 84,689 28,137 112,826 2021 75,929 27,974 103,903 2022 64,064 25,591 89,655 2023 54,168 24,401 78,569 Thereafter 143,714 107,146 250,860 Total minimum lease payments $ 512,153 $ 239,810 $ 751,963 1 Represents the portion of future minimum lease payments relating to facility leases where the Company was determined to be the accounting owner (see Note 1). These payments are recognized as reductions to the financing obligation and as interest expense and exclude the future non-cash termination of the financing obligation.
Future minimum lease payments, financing obligations	As of September 30, 2018 , future minimum rental payments under noncancelable operating leases and financing obligations were as follows: Payments Due by Fiscal Year (in thousands) Operating Leases Financing Obligations 1 Total 2019 $ 89,589 $ 26,561 $ 116,150 2020 84,689 28,137 112,826 2021 75,929 27,974 103,903 2022 64,064 25,591 89,655 2023 54,168 24,401 78,569 Thereafter 143,714 107,146 250,860 Total minimum lease payments $ 512,153 $ 239,810 $ 751,963 1 Represents the portion of future minimum lease payments relating to facility leases where the Company was determined to be the accounting owner (see Note 1). These payments are recognized as reductions to the financing obligation and as interest expense and exclude the future non-cash termination of the financing obligation.

Employee Severance, Litigatio_2

Employee Severance, Litigation, and Other (Tables)	12 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Employee severance, litigation, and other charges	The following illustrates the charges incurred by the Company relating to Employee Severance, Litigation, and Other for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Employee severance $ 36,694 $ 7,767 $ 38,786 Litigation and opioid-related costs 61,527 917,573 — Transfer of surplus plan assets — — 17,149 Customer contract dispute settlements — — 13,000 Other 85,299 33,987 33,976 Total employee severance, litigation, and other $ 183,520 $ 959,327 $ 102,911

Business Segment Information (T

Business Segment Information (Tables)	12 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Reconciliation of revenue from segments to consolidated	The following illustrates reportable segment revenue information for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 161,699,343 $ 147,453,495 $ 141,701,997 Other 6,332,730 5,747,863 5,207,095 Intersegment eliminations (92,438 ) (57,532 ) (59,406 ) Revenue $ 167,939,635 $ 153,143,826 $ 146,849,686
Reconciliation of segment operating income, depreciation and amortization, and capital expenditures from segments to consolidated	The following illustrates capital expenditures by reportable segment for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 190,191 $ 339,478 $ 359,391 Other 146,220 126,919 105,225 Total capital expenditures $ 336,411 $ 466,397 $ 464,616 The following illustrates depreciation and amortization by reportable segment for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 225,608 $ 188,065 $ 170,973 Other 64,768 53,160 46,500 Acquisition-related intangibles amortization 174,751 156,378 147,262 Total depreciation and amortization $ 465,127 $ 397,603 $ 364,735 The following illustrates reportable segment operating income information for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 1,626,748 $ 1,643,629 $ 1,702,725 Other 355,091 373,797 327,746 Intersegment eliminations (609 ) (556 ) (103 ) Total segment operating income $ 1,981,230 $ 2,016,870 $ 2,030,368
Reconciliation of total segment operating income to income from continuing operations before income taxes	The following reconciles total segment operating income to income before income taxes for the periods indicated: Fiscal Year Ended September 30, (in thousands) 2018 2017 2016 Total segment operating income $ 1,981,230 $ 2,016,870 $ 2,030,368 Gain from antitrust litigation settlements 35,938 1,395 133,758 LIFO (expense) credit (67,324 ) 157,782 (200,230 ) PharMEDium remediation costs (66,204 ) — — New York State Opioid Stewardship Act (22,000 ) — — Acquisition-related intangibles amortization (174,751 ) (156,378 ) (147,262 ) Warrants expense — — (140,342 ) Employee severance, litigation, and other (183,520 ) (959,327 ) (102,911 ) Pension settlement charge — — (47,607 ) Goodwill impairment (59,684 ) — — Operating income 1,443,685 1,060,342 1,525,774 Other loss (income) 25,469 (2,730 ) (5,048 ) Interest expense, net 174,699 145,185 139,912 Loss on consolidation of equity investments 42,328 — — Loss on early retirement of debt 23,766 — — Income before income taxes $ 1,177,423 $ 917,887 $ 1,390,910
Reconciliation of assets from segment to consolidated	The following illustrates total assets by reportable segment for the periods indicated: September 30, (in thousands) 2018 2017 2016 Pharmaceutical Distribution Services $ 31,892,621 $ 29,691,127 $ 28,605,047 Other 5,777,217 5,625,343 5,032,454 Total assets $ 37,669,838 $ 35,316,470 $ 33,637,501

Quarterly Financial Informati_2

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly financial information	Fiscal Year Ended September 30, 2018 (in thousands, except per share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter Fiscal Year Revenue $ 40,466,332 $ 41,033,858 $ 43,142,309 $ 43,297,136 $ 167,939,635 Gross profit (a) $ 1,112,652 $ 1,255,683 $ 1,211,341 $ 1,032,641 $ 4,612,317 Distribution, selling, and administrative expenses; depreciation; and amortization 663,658 736,814 746,593 778,363 2,925,428 Employee severance, litigation, and other 30,021 37,449 75,553 40,497 183,520 Goodwill impairment — — — 59,684 59,684 Operating income $ 418,973 $ 481,420 $ 389,195 $ 154,097 $ 1,443,685 Net income (b) $ 861,853 $ 282,160 $ 277,875 $ 194,004 $ 1,615,892 Net income attributable to AmerisourceBergen Corporation (b) $ 861,853 $ 287,455 $ 275,809 $ 233,288 $ 1,658,405 Earnings per share operations: Basic $ 3.95 $ 1.31 $ 1.26 $ 1.08 $ 7.61 Diluted $ 3.90 $ 1.29 $ 1.25 $ 1.07 $ 7.53 __________________________________________________________ (a) The second and third quarters of the fiscal year ended September 30, 2018 include gains from antitrust litigation settlements of $0.3 million and $35.6 million . The third quarter of the fiscal year ended September 30, 2018 includes a LIFO credit of $16.1 million . The fourth quarter of the fiscal year ended September 30, 2018 includes LIFO expense of $83.5 million . The second, third, and fourth quarters of the fiscal year ended September 30, 2018 include PharMEDium remediation costs of $22.5 million , $12.0 million , and $26.6 million . The fourth quarter of the fiscal year ended September 30, 2018 includes a $22.0 million estimate of our liability under the New York State Opioid Stewardship Act. (b) The first quarter of the fiscal year ended September 30, 2018 includes a loss on early retirement of debt of $23.8 million . The second quarter of the fiscal year ended September 30, 2018 includes a $42.3 million loss on consolidation of equity investments and a $30.0 million impairment of a non-customer note receivable. The first and fourth quarters of the fiscal year ended September 30, 2018 included discrete income tax benefits recognized in connection with the 2017 Tax Act of $587.6 million and $25.0 million , respectively. Fiscal Year Ended September 30, 2017 (in thousands, except per share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter Fiscal Year Revenue $ 38,169,265 $ 37,147,402 $ 38,707,144 $ 39,120,015 $ 153,143,826 Gross profit (a) $ 1,037,680 $ 1,256,427 $ 1,079,875 $ 1,172,020 $ 4,546,002 Distribution, selling, and administrative expenses; depreciation; and amortization 616,627 619,512 624,982 665,212 2,526,333 Employee severance, litigation, and other (b) 21,066 11,934 284,517 641,810 959,327 Operating income (loss) $ 399,987 $ 624,981 $ 170,376 $ (135,002 ) $ 1,060,342 Net income (loss) $ 247,246 $ 411,473 $ 50,352 $ (344,587 ) $ 364,484 Earnings per share operations: Basic $ 1.13 $ 1.89 $ 0.23 $ (1.58 ) $ 1.67 Diluted $ 1.11 $ 1.86 $ 0.23 $ (1.58 ) $ 1.64 __________________________________________________________ (a) The first quarter of the fiscal year ended September 30, 2017 includes gains from antitrust and litigation settlements of $1.4 million . The first quarter of the fiscal year ended September 30, 2017 includes LIFO expense of $28.3 million . The second, third, and fourth quarters of the fiscal year ended September 30, 2017 include LIFO credits of $86.5 million , $24.7 million , and $74.9 million , respectively. (b) The third quarter of the fiscal year ended September 30, 2017 includes $273.4 million for litigation settlements. The fourth quarter of the fiscal year ended September 30, 2017 includes a $625.0 million litigation accrual.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment, share-based compensation				$ 47,063
Deferred tax asset	$ 548,287	$ 604,210
Accounting Standards Update 2016-09 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax asset			$ 47,100
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment, share-based compensation				$ 47,063
Retained Earnings [Member] | Accounting Standards Update 2016-09 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment, share-based compensation			$ 47,100

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Concentrations of Credit Risk (Details)	12 Months Ended
	Sep. 30, 2018
Walgreens Boots Alliance, Inc. [Member]
Concentration Risk [Line Items]
Major customer, percentage of revenue	33.00%
Major customer, percentage of accounts receivable	49.00%
Express Scripts, Inc. [Member]
Concentration Risk [Line Items]
Major customer, percentage of revenue	13.00%
Major customer, percentage of accounts receivable	8.00%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Derivative Financial Instruments (Details) $ in Millions	Sep. 30, 2018CAD ($)contract
Accounting Policies [Abstract]
Number of foreign currency denominated contracts outstanding | contract	1
Discontinued operations, note due from buyer | $	$ 17.5

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details) - USD ($)	3 Months Ended				12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Assets Held and Used [Line Items]
Goodwill impairment	$ 59,684,000	$ 0	$ 0	$ 0	$ 59,684,000	$ 0	$ 0
Other intangible assets impairment charge					0	$ 0	$ 0
PharMEDium Healthcare Holdings, Inc [Member]
Assets Held and Used [Line Items]
Carrying value of assets excluding goodwill	$ 903,000,000				$ 903,000,000

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Investment Securities Available-For-Sale (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2017
Prepaid Expenses and Other [Member]
Debt Securities, Available-for-sale [Abstract]
Available-for-sale securities	$ 0	$ 0

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Merchandise Inventories (Details) - USD ($) $ in Thousands	3 Months Ended						12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Percentage of inventories, cost determined using LIFO	75.00%		80.00%				75.00%	80.00%
Excess cost of inventories over LIFO, if used FIFO	$ 1,534,400		$ 1,467,000				$ 1,534,400	$ 1,467,000
LIFO charges (credit)	$ 83,500	$ (16,100)	$ (74,900)	$ (24,700)	$ (86,500)	$ 28,300	$ 67,324	$ (157,782)	$ 200,230

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Sep. 30, 2018
Building and improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Building and improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	40 years
Machinery, equipment and other [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Machinery, equipment and other [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Software and software development costs [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Software and software development costs [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Accounting Policies [Abstract]
Accrual for estimated customer sales returns	$ 988.8	$ 1,001.7

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Shipping and Handling Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Shipping and Handling [Line Items]
Cost of goods sold	$ 163,327,318	$ 148,597,824	$ 142,577,080
Shipping and Handling [Member]
Shipping and Handling [Line Items]
Cost of goods sold	$ 590,800	$ 517,300	$ 494,700

Acquisitions and Investments -

Acquisitions and Investments - PharMEDium (Details) - USD ($) $ in Thousands	Nov. 06, 2015	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Goodwill		$ 6,664,272	$ 6,044,281	$ 5,991,497
PharMEDium Healthcare Holdings, Inc [Member]
Business Acquisition [Line Items]
Cash paid to acquire business, including purchase price adjustments	$ 2,700,000
Goodwill	1,800,000
Estimated fair value of accounts receivables	63,200
Estimated fair value of inventory	43,100
Estimated fair value of accounts payable	22,800
Estimated fair value of the intangible assets acquired	1,100,000
Deferred tax liability	356,100
PharMEDium Healthcare Holdings, Inc [Member] | Customer relationships [Member]
Business Acquisition [Line Items]
Estimated fair value of the intangible assets acquired, finite-lived	$ 882,700
Estimated useful life (in years)	15 years
PharMEDium Healthcare Holdings, Inc [Member] | Trade names [Member]
Business Acquisition [Line Items]
Estimated fair value of the intangible assets acquired, finite-lived	$ 167,600
Estimated useful life (in years)	15 years
PharMEDium Healthcare Holdings, Inc [Member] | Software technology [Member]
Business Acquisition [Line Items]
Estimated fair value of the intangible assets acquired, finite-lived	$ 52,600
Estimated useful life (in years)	10 years

Acquisitions and Investments _2

Acquisitions and Investments - NEVSCO (Details) - USD ($) $ in Thousands	1 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Goodwill		$ 6,664,272	$ 6,044,281	$ 5,991,497
Northeast Veterinary Supply Company NEVSCO [Member]
Business Acquisition [Line Items]
Cash paid to acquire business, including purchase price adjustments	$ 70,000
Goodwill	30,900
Estimated fair value of accounts receivable	10,300
Estimated fair value of inventory	6,700
Estimated fair value of accounts payable and accrued expenses	3,000
Estimated fair value of the intangible assets acquired, finite-lived	$ 29,800
Customer relationships [Member] | Northeast Veterinary Supply Company NEVSCO [Member]
Business Acquisition [Line Items]
Estimated useful life (in years)	15 years

Acquisitions and Investments _3

Acquisitions and Investments - H.D. Smith (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired		$ 785,299	$ 61,648	$ 2,731,356
Goodwill		6,664,272	6,044,281	$ 5,991,497
Net deferred tax liabilities		$ 1,829,410	$ 2,492,612
H.D. Smith [Member]
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired	$ 815,000
Goodwill	499,900
Estimated fair value of accounts receivable	163,100
Estimated fair value of inventory	350,700
Estimated fair value of accounts payable and accrued expenses	366,100
Estimated fair value of the intangible assets acquired, finite-lived	167,800
Net deferred tax liabilities	60,600
Customer relationships [Member] | H.D. Smith [Member]
Business Acquisition [Line Items]
Estimated fair value of the intangible assets acquired, finite-lived	$ 156,600
Estimated useful life (in years)	12 years
Trade names [Member] | H.D. Smith [Member]
Business Acquisition [Line Items]
Estimated fair value of the intangible assets acquired, finite-lived	$ 11,200
Estimated useful life (in years)	2 years

Acquisitions and Investments _4

Acquisitions and Investments - Proforma and Specialty Joint Venture (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Sep. 30, 2018	Jan. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2018
Business Acquisition [Line Items]
Investment in Profarma			$ 0	$ 11,347	$ 19,034
Goodwill	$ 6,664,272		6,664,272	6,044,281	5,991,497
Net deferred tax liabilities	1,829,410		1,829,410	2,492,612
Loss on consolidation of equity investments			42,328	0	0
Foreign currency translation adjustment from AOCI			$ (45,941)	$ 0	$ 0
Profarma Distribuidora de Produtos Farmaceuticos S.A. [Member]
Business Acquisition [Line Items]
Investment in Profarma		$ 62,500
Ownership interest in Profarma						38.20%
Goodwill		142,000
Estimated fair value of accounts receivable		160,100
Estimated fair value of inventory		190,500
Estimated fair value of accounts payable and accrued expenses		167,700
Assumed short-term debt		209,900
Assumed long-term debt		12,400
Assumed cash		150,800
Noncontrolling interest		168,000
Estimated fair value of the intangible assets acquired, finite-lived		84,600
Net deferred tax liabilities		50,100
Profarma Joint Venture [Member]
Business Acquisition [Line Items]
Investment in specialty joint venture	$ 23,600	15,600
Ownership in specialty joint venture	89.90%		89.90%			64.50%
Goodwill		3,500
Estimated fair value of accounts receivable		65,000
Estimated fair value of inventory		29,100
Estimated fair value of accounts payable and accrued expenses		54,300
Assumed short-term debt		32,700
Assumed cash		28,900
Estimated fair value of the intangible assets acquired, finite-lived		$ 4,600
Estimated useful life (in years)		15 years
Loss on consolidation of equity investments			$ 8,800
Gain on remeasurement of Profarma's previously held equity interest			12,400
Customer relationships [Member] | Profarma Distribuidora de Produtos Farmaceuticos S.A. [Member]
Business Acquisition [Line Items]
Estimated fair value of the intangible assets acquired, finite-lived		$ 25,900
Customer relationships [Member] | Profarma Joint Venture [Member]
Business Acquisition [Line Items]
Estimated useful life (in years)		15 years
Trade names [Member] | Profarma Distribuidora de Produtos Farmaceuticos S.A. [Member]
Business Acquisition [Line Items]
Estimated fair value of the intangible assets acquired, finite-lived		$ 58,700
Foreign currency translation [Member]
Business Acquisition [Line Items]
Foreign currency translation adjustment from AOCI			$ 45,900
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Profarma Distribuidora de Produtos Farmaceuticos S.A. [Member]
Business Acquisition [Line Items]
Fair value of equity interests		103,100
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Profarma Joint Venture [Member]
Business Acquisition [Line Items]
Fair value of equity interests		$ 31,200
Minimum [Member] | Trade names [Member] | Profarma Distribuidora de Produtos Farmaceuticos S.A. [Member]
Business Acquisition [Line Items]
Estimated useful life (in years)		15 years
Maximum [Member] | Trade names [Member] | Profarma Distribuidora de Produtos Farmaceuticos S.A. [Member]
Business Acquisition [Line Items]
Estimated useful life (in years)		25 years

Variable Interest Entity (Detai

Variable Interest Entity (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 2,492,516	$ 2,435,115	$ 2,741,832	$ 2,167,442
Merchandise inventories	11,918,508	11,461,428
Property and equipment, net	1,892,424	1,797,945
Goodwill	6,664,272	6,044,281	5,991,497
Other long-term assets	270,942	337,664
TOTAL ASSETS	37,669,838	35,316,470	$ 33,637,501
Deferred income taxes	1,829,410	2,492,612
Other long-term liabilities	110,352	$ 75,406
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	26,801
Accounts receivables, net	144,646
Merchandise inventories	168,931
Prepaid expenses and other	61,924
Property and equipment, net	32,667
Goodwill	82,309
Other intangible assets	80,974
Other long-term assets	8,912
TOTAL ASSETS	607,164
Accounts payable	150,102
Accrued expenses and other	37,195
Short-term debt	115,461
Long-term debt	39,704
Deferred income taxes	46,137
Other long-term liabilities	31,988
Total liabilities	$ 420,587

Income Taxes - Domestic and For

Income Taxes - Domestic and Foreign Income From Continuing Operations Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Domestic	$ 704,935	$ 394,721	$ 906,415
Foreign	472,488	523,166	484,495
Income before income taxes	$ 1,177,423	$ 917,887	$ 1,390,910

Income Taxes - Income Tax Provi

Income Taxes - Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Current provision:
Federal	$ 247,755	$ 141,071	$ 11,892
State and local	39,328	35,950	26,741
Foreign	69,972	57,313	55,275
Provision for income taxes, current	357,055	234,334	93,908
Deferred (benefit) provision:
Federal	(828,023)	265,074	(119,218)
State and local	33,887	54,995	(11,490)
Foreign	(1,388)	(1,000)	(219)
Provision for income taxes, deferred	(795,524)	319,069	(130,927)
(Benefit) provision for income taxes	$ (438,469)	$ 553,403	$ (37,019)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Effective Income Tax Rate (Details)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Statutory U.S. federal income tax rate	24.50%	35.00%	35.00%
State and local income tax rate, net of federal tax benefit	(0.10%)	5.40%	0.60%
Foreign	(6.20%)	(14.60%)	(8.40%)
Warrants	0.00%	0.00%	(32.80%)
Valuation allowance	(1.40%)	2.20%	2.20%
Excess tax benefits related to share-based compensation	(1.80%)	(3.80%)	(0.00%)
Litigation settlements and accruals (see Note 13)	(6.30%)	34.30%	0.00%
Goodwill impairment (see Note 5)	1.70%	0.00%	0.00%
Tax reform	(52.00%)	0.00%	0.00%
Capital gain on distribution	3.60%	0.00%	0.00%
Other	0.80%	1.80%	0.70%
Effective income tax rate	(37.20%)	60.30%	(2.70%)

Income Taxes - Significant Comp

Income Taxes - Significant Components of Deferred Tax Liabilities (Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Components of Deferred Tax Assets and Liabilities [Abstract]
Merchandise inventories	$ 1,189,801	$ 1,519,779
Property and equipment	133,417	150,240
Goodwill and other intangible assets	853,747	1,214,597
Other	747	1,126
Gross deferred tax liabilities	2,177,712	2,885,742
Net operating loss and tax credit carryforwards	(421,808)	(320,180)
Capital loss carryforwards	0	(64,346)
Allowance for doubtful accounts	(20,126)	(25,871)
Accrued expenses	(17,363)	(36,188)
Employee and retiree benefits	(10,210)	(17,121)
Share-based compensation	(28,888)	(59,495)
Other	(49,892)	(81,009)
Gross deferred tax assets	(548,287)	(604,210)
Valuation allowance for deferred tax assets	199,985	211,080
Deferred tax assets, net of valuation allowance	(348,302)	(393,130)
Net deferred tax liabilities	$ 1,829,410	$ 2,492,612

Income Taxes - Reconciliation_2

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of period	$ 323,869	$ 75,766	$ 44,722
Additions of tax positions of the current year	2,804	252,866	24,145
Additions to tax positions of the prior years	558	1,049	11,840
Reductions of tax positions of the prior years	(224,878)	(668)	(1,407)
Settlements with taxing authorities	(1,847)	(3,285)	(2,589)
Expiration of statutes of limitations	(2,382)	(1,859)	(945)
Unrecognized tax benefits at end of period	$ 98,124	$ 323,869	$ 75,766

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	Sep. 30, 2018	Sep. 28, 2018	Nov. 30, 2015	Mar. 31, 2013	Sep. 30, 2018	Dec. 31, 2017	Jun. 30, 2018	Aug. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Operating Loss Carryforwards [Line Items]
Tax Cuts and Jobs Act, recognized income tax benefits					$ 25,000,000	$ 587,600,000			$ 612,600,000
Tax Cuts and Jobs Act, deferred income tax benefit as result of applying a lower U.S. federal income tax rate									897,600,000
Tax Cuts and Jobs Act, current income tax expense on historical foreign earnings and profits							$ 310,000,000
Tax Cuts and Jobs Act, decrease in provisional transition tax					25,000,000
Tax Cuts And Jobs Act, transition tax									219,600,000
Undistributed earnings of international subsidiaries	$ 1,900,000,000				1,900,000,000				1,900,000,000
Permanently reinvested cumulative undistributed earnings	1,100,000,000				1,100,000,000				1,100,000,000
Valuation allowance - increase (decrease)									(11,100,000)	$ 45,500,000
Excess tax benefit from the exercise of stock options and lapses of restricted stock units									22,700,000	36,700,000	$ 0
Income tax payments, net of refunds									104,000,000	105,000,000	17,500,000
Unrecognized tax benefits, including interest and penalties	112,900,000				112,900,000				112,900,000	338,400,000
Unrecognized tax benefits, including interest and penalties, net of federal benefit	89,400,000				89,400,000				89,400,000	304,200,000
Unrecognized tax benefits that would impact effective tax rate	71,100,000				71,100,000				71,100,000	289,200,000
Unrecognized tax benefits, interest and penalties	14,800,000				14,800,000				14,800,000	14,500,000
Litigation settlement, unrecognized tax benefit	98,124,000				98,124,000				98,124,000	323,869,000	75,766,000	$ 44,722,000
Reductions of tax positions of the prior years									224,878,000	668,000	$ 1,407,000
Reduction of unrecognized tax benefits reasonably possible	14,700,000				14,700,000				14,700,000
Value of warrants				$ 242,400,000				$ 1,565,900,000
Term of warrants (in years)				10 years
Tax benefit adjustment, increase in fair value of warrants			$ 456,000,000					$ 52,000,000
Federal [Member]
Operating Loss Carryforwards [Line Items]
Potential tax benefits from net operating loss carryforwards	89,700,000				89,700,000				89,700,000
Potential tax benefits from net operating loss carryforwards subject to expiration	75,500,000				75,500,000				75,500,000
Federal [Member] | Alternative minimum tax credit carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 122,900,000				122,900,000				122,900,000
Federal [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, term (in years)	1 year
Federal [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, term (in years)	19 years
State [Member]
Operating Loss Carryforwards [Line Items]
Potential tax benefits from net operating loss carryforwards	$ 172,000,000				172,000,000				172,000,000
Tax credit carryforwards	$ 3,900,000				3,900,000				3,900,000
State [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, term (in years)	1 year
State [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, term (in years)	20 years
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Potential tax benefits from net operating loss carryforwards	$ 49,500,000				49,500,000				49,500,000
Foreign [Member] | Alternative minimum tax credit carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	2,100,000				2,100,000				2,100,000
USAO-EDNY Matter [Member]
Operating Loss Carryforwards [Line Items]
Litigation settlement, unrecognized tax benefit	$ 235,100,000				$ 235,100,000				$ 235,100,000
Litigation settlement, accrued reserve										625,000,000
USAO - EDNY Civil Claims [Member]
Operating Loss Carryforwards [Line Items]
Litigation settlement, accrued reserve										625,000,000
Litigation settlement, payment		$ 625,000,000
Accounting Standards Update 2016-09 [Member]
Operating Loss Carryforwards [Line Items]
Valuation allowance - increase (decrease)										$ 17,100,000

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Changes in Carrying Value of Goodwill (Details) - USD ($)	3 Months Ended				12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Goodwill [Roll Forward]
Beginning balance				$ 6,044,281,000	$ 6,044,281,000	$ 5,991,497,000
Goodwill recognized in connection with acquisitions					681,261,000	54,151,000
Goodwill disposed in connection with divestiture						(3,564,000)
Goodwill impairment	$ (59,684,000)	$ 0	$ 0	0	(59,684,000)	0	$ 0
Foreign currency translation					(1,586,000)	2,197,000
Ending balance	6,664,272,000				6,664,272,000	6,044,281,000	5,991,497,000
Operating segments [Member] | Pharmaceutical Distribution [Member]
Goodwill [Roll Forward]
Beginning balance				4,270,550,000	4,270,550,000	4,270,550,000
Goodwill recognized in connection with acquisitions					641,909,000	0
Goodwill disposed in connection with divestiture						0
Goodwill impairment					(59,684,000)
Foreign currency translation					0	0
Ending balance	4,852,775,000				4,852,775,000	4,270,550,000	4,270,550,000
Operating segments [Member] | Other [Member]
Goodwill [Roll Forward]
Beginning balance				$ 1,773,731,000	1,773,731,000	1,720,947,000
Goodwill recognized in connection with acquisitions					39,352,000	54,151,000
Goodwill disposed in connection with divestiture						(3,564,000)
Goodwill impairment					0
Foreign currency translation					(1,586,000)	2,197,000
Ending balance	$ 1,811,497,000				$ 1,811,497,000	$ 1,773,731,000	$ 1,720,947,000

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangibles, accumulated amortization	$ (684,743)	$ (506,825)
Total other intangible assets, gross carrying amount	3,632,571	3,340,106
Total other intangible assets, net carrying amount	2,947,828	2,833,281
Trade names [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived intangibles	$ 685,380	685,088
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, weighted average remaining useful life	14 years
Finite-lived intangibles, gross carrying amount	$ 2,549,245	2,329,665
Finite-lived intangibles, accumulated amortization	(555,440)	(408,636)
Finite-lived intangibles, net carrying amount	$ 1,993,805	1,921,029
Trade names and other [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, weighted average remaining useful life	13 years
Finite-lived intangibles, gross carrying amount	$ 397,946	325,353
Finite-lived intangibles, accumulated amortization	(129,303)	(98,189)
Finite-lived intangibles, net carrying amount	$ 268,643	$ 227,164

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Additional Information (Details) - USD ($)	3 Months Ended				12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 59,684,000	$ 0	$ 0	$ 0	$ 59,684,000	$ 0	$ 0
Amortization expense, fiscal year maturity
Amortization expense					181,156,000	$ 160,503,000	$ 152,493,000
2,018	182,900,000				182,900,000
2,019	175,400,000				175,400,000
2,020	171,400,000				171,400,000
2,021	170,100,000				170,100,000
2,022	169,100,000				169,100,000
Thereafter	$ 1,393,500,000				$ 1,393,500,000

Debt - Debt Instruments (Detail

Debt - Debt Instruments (Details)	Sep. 30, 2018USD ($)	Sep. 30, 2018GBP (£)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)
Debt Instrument [Line Items]
Capital lease obligations	$ 745,000			$ 0
Total debt	4,310,189,000			3,442,055,000
Less nonrecourse current portion	13,976,000			12,121,000
Total, net of current portion	4,158,532,000			3,429,934,000
Revolving credit note [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	75,000,000
Debt	0			0
Receivables securitization facility due 2019 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	1,450,000,000
Debt	500,000,000			500,000,000
Term loans due in 2020 [Member]
Debt Instrument [Line Items]
Debt	398,665,000			547,860,000
Multi-currency revolving credit facility due 2021 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	1,400,000,000
Debt	0			0
Overdraft facility due in 2021 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity | £		£ 30,000,000
Debt	13,269,000			12,121,000
$400,000, 4.875% senior notes due 2019 [Member]
Debt Instrument [Line Items]
Principal amount	$ 400,000,000		$ 400,000,000
Interest rate	4.875%	4.875%	4.875%
Debt	$ 0			398,399,000
$500,000, 3.50% senior notes due 2021 [Member]
Debt Instrument [Line Items]
Principal amount	$ 500,000,000
Interest rate	3.50%	3.50%
Debt	$ 498,392,000			497,877,000
$500,000, 3.40% senior notes due 2024 [Member]
Debt Instrument [Line Items]
Principal amount	$ 500,000,000
Interest rate	3.40%	3.40%
Debt	$ 497,255,000			496,766,000
$500,000, 3.25% senior notes due 2025 [Member]
Debt Instrument [Line Items]
Principal amount	$ 500,000,000
Interest rate	3.25%	3.25%
Debt	$ 495,632,000			494,950,000
$750,000, 3.45% senior notes due 2027 [Member]
Debt Instrument [Line Items]
Principal amount	$ 750,000,000		$ 750,000,000
Interest rate	3.45%	3.45%	3.45%
Debt	$ 742,258,000			0
$500,000, 4.25% senior notes due 2045 [Member]
Debt Instrument [Line Items]
Principal amount	$ 500,000,000
Interest rate	4.25%	4.25%
Debt	$ 494,298,000			494,082,000
$500,000, 4.3% senior notes due 2047 [Member]
Debt Instrument [Line Items]
Principal amount			$ 500,000,000
Interest rate			4.30%
Debt	492,222,000			0
Non-recourse Debt [Member]
Debt Instrument [Line Items]
Debt	177,453,000			0
Less nonrecourse current portion	$ 137,681,000			$ 0

Debt - Additional Information (

Debt - Additional Information (Details)	1 Months Ended					12 Months Ended			36 Months Ended	44 Months Ended
	Oct. 31, 2018	Dec. 31, 2017USD ($)	May 31, 2017USD ($)	Nov. 30, 2015USD ($)	Feb. 28, 2015USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2018GBP (£)
Debt Instrument [Line Items]
Repayments of term loan and senior notes						$ 681,001,000	$ 750,000,000	$ 800,000,000
Payment of premium on early retirement of debt		$ 22,300,000				22,348,000	0	0
Scheduled future principal payments, in fiscal 2019						148,800,000			$ 148,800,000	$ 148,800,000
Scheduled future principal payments, in fiscal 2020						595,700,000			595,700,000	595,700,000
Scheduled future principal payments, in fiscal 2021						336,900,000			336,900,000	336,900,000
Scheduled future principal payments, in fiscal 2022						500,000,000			500,000,000	500,000,000
Scheduled future principal payments, in fiscal 2023						0			0	0
Scheduled future principal payments, thereafter						2,800,000,000			2,800,000,000	2,800,000,000
Interest paid						162,100,000	125,300,000	123,500,000
Amortization of financing fees and accretion of original issue discounts						7,700,000	6,200,000	$ 6,300,000
$750,000, 3.45% senior notes due 2027 [Member]
Debt Instrument [Line Items]
Principal amount		$ 750,000,000				$ 750,000,000			$ 750,000,000	$ 750,000,000
Interest rate		3.45%				3.45%			3.45%	3.45%	3.45%
Percentage of principal amount		99.76%
Effective yield percentage		3.48%
$500,000, 4.3% senior notes due 2047 [Member]
Debt Instrument [Line Items]
Principal amount		$ 500,000,000
Interest rate		4.30%
Percentage of principal amount		99.51%
Effective yield percentage		4.33%
Multi-currency revolving credit facility due 2021 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 1,400,000,000			$ 1,400,000,000	$ 1,400,000,000
Minimum facility fee rate						0.05%
Maximum facility fee rate						0.15%
Facility fee, period end						0.09%
Commercial paper [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 1,400,000,000			1,400,000,000	1,400,000,000
Short-term debt						0	$ 0		0	0
Receivables securitization facility due 2019 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity						1,450,000,000			1,450,000,000	1,450,000,000
Accordion feature, potential increase in commitment						250,000,000			250,000,000	250,000,000
Revolving credit note [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity						75,000,000			75,000,000	75,000,000
Overdraft facility due in 2021 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity | £											£ 30,000,000
February 2015 term loan [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity					$ 1,000,000,000
Repayments of term loan and senior notes										925,000,000
November 2015 term loan [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 1,000,000,000
Repayments of term loan and senior notes									675,000,000
$500,000, 3.25% senior notes due 2025 [Member]
Debt Instrument [Line Items]
Principal amount						$ 500,000,000			$ 500,000,000	$ 500,000,000
Interest rate						3.25%			3.25%	3.25%	3.25%
$500,000, 4.25% senior notes due 2045 [Member]
Debt Instrument [Line Items]
Principal amount						$ 500,000,000			$ 500,000,000	$ 500,000,000
Interest rate						4.25%			4.25%	4.25%	4.25%
$600,000, 1.15% senior notes due 2017 [Member]
Debt Instrument [Line Items]
Interest rate			1.15%
Repayments of term loan and senior notes			$ 600,000,000
$500,000, 3.40% senior notes due 2024 [Member]
Debt Instrument [Line Items]
Principal amount						$ 500,000,000			$ 500,000,000	$ 500,000,000
Interest rate						3.40%			3.40%	3.40%	3.40%
$400,000, 4.875% senior notes due 2019 [Member]
Debt Instrument [Line Items]
Principal amount		$ 400,000,000				$ 400,000,000			$ 400,000,000	$ 400,000,000
Interest rate		4.875%				4.875%			4.875%	4.875%	4.875%
$500,000, 3.50% senior notes due 2021 [Member]
Debt Instrument [Line Items]
Principal amount						$ 500,000,000			$ 500,000,000	$ 500,000,000
Interest rate						3.50%			3.50%	3.50%	3.50%
CDOR / LIBOR / EURIBOR / Bankers Acceptance Stamping Fee [Member] | Multi-currency revolving credit facility due 2021 [Member]
Debt Instrument [Line Items]
Variable rate spread						0.91%
CDOR / LIBOR / EURIBOR / Bankers Acceptance Stamping Fee [Member] | Minimum [Member] | Multi-currency revolving credit facility due 2021 [Member]
Debt Instrument [Line Items]
Variable rate spread						0.70%
CDOR / LIBOR / EURIBOR / Bankers Acceptance Stamping Fee [Member] | Maximum [Member] | Multi-currency revolving credit facility due 2021 [Member]
Debt Instrument [Line Items]
Variable rate spread						1.10%
Alternate base rate and Canadian prime rate [Member] | Minimum [Member] | Multi-currency revolving credit facility due 2021 [Member]
Debt Instrument [Line Items]
Variable rate spread						0.00%
Alternate base rate and Canadian prime rate [Member] | Maximum [Member] | Multi-currency revolving credit facility due 2021 [Member]
Debt Instrument [Line Items]
Variable rate spread						0.10%
LIBOR [Member] | February 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread						1.00%
LIBOR [Member] | November 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread						1.00%
LIBOR [Member] | Minimum [Member] | February 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread					0.75%
LIBOR [Member] | Minimum [Member] | November 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread				0.75%
LIBOR [Member] | Maximum [Member] | February 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread					1.25%
LIBOR [Member] | Maximum [Member] | November 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread				1.25%
Base rate [Member] | Minimum [Member] | February 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread					0.00%
Base rate [Member] | Minimum [Member] | November 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread				0.00%
Base rate [Member] | Maximum [Member] | February 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread					0.25%
Base rate [Member] | Maximum [Member] | November 2015 term loan [Member]
Debt Instrument [Line Items]
Variable rate spread				0.25%
Subsequent Event [Member] | LIBOR [Member] | Term Loan Agreement October 2018 [Member]
Debt Instrument [Line Items]
Variable rate spread	0.65%

Stockholders' Equity and Weig_3

Stockholders' Equity and Weighted Average Common Shares Outstanding - Additional Information (Details) - USD ($)

1 Months Ended

5 Months Ended

6 Months Ended

12 Months Ended

31 Months Ended

Oct. 31, 2018

Nov. 30, 2016

Sep. 30, 2016

Aug. 31, 2016

Mar. 31, 2013

Sep. 30, 2016

Mar. 31, 2016

Sep. 30, 2018

Sep. 30, 2017

Sep. 30, 2016

Dec. 31, 2015

May 31, 2016

Aug. 31, 2013

Equity, Class of Treasury Stock [Line Items]

Common stock, authorized (shares)

600,000,000

600,000,000

Common stock, par value (usd per share)

$ 0.01

$ 0.01

Preferred stock, authorized (shares)

10,000,000

Preferred stock, par value (usd per share)

$ 0.01

Preferred stock, issued (shares)

0

Shares repurchased

$ 663,220,000

$ 329,929,000

$ 1,866,344,000

Shares to which framework agreement allows open market purchases (shares)

19,859,795

Percentage of common stock to which framework agreement allows open market purchases

7.00%

Antidilutive securities excluded from computation of diluted earnings per share (shares)

3,200,000

4,100,000

3,100,000

Treasury Stock [Member]

Equity, Class of Treasury Stock [Line Items]

Shares repurchased

$ 663,220,000

$ 329,929,000

$ 1,866,344,000

Walgreens Warrant 1 (2016 Warrants) [Member]

Equity, Class of Treasury Stock [Line Items]

Warrants (shares)

22,696,912

Warrants, exercise price (usd per share)

$ 51.50

Warrants, exercise period (in months)

6 months

Walgreens Warrant 1 (2016 Warrants) [Member] | Walgreens Boots Alliance, Inc. [Member] | Investor [Member]

Equity, Class of Treasury Stock [Line Items]

Exercises of warrants

$ 1,168,900,000

Walgreens Warrant 1 (2016 Warrants) [Member] | Walgreens Boots Alliance, Inc. [Member] | Investor [Member] | Treasury Stock [Member]

Equity, Class of Treasury Stock [Line Items]

Exercises of warrants

866,000,000

Walgreens Warrant 1 (2016 Warrants) [Member] | Walgreens Boots Alliance, Inc. [Member] | Investor [Member] | Additional Paid-in Capital [Member]

Equity, Class of Treasury Stock [Line Items]

Exercises of warrants

$ 302,900,000

Walgreens Warrant 2 (2017 Warrants) [Member]

Equity, Class of Treasury Stock [Line Items]

Warrants (shares)

22,696,912

Warrants, exercise price (usd per share)

$ 52.50

$ 52.50

Warrants, exercise period (in months)

6 months

6 months

Walgreens Warrant 2 (2017 Warrants) [Member] | Walgreens Boots Alliance, Inc. [Member] | Investor [Member]

Equity, Class of Treasury Stock [Line Items]

Exercises of warrants

$ 1,191,600,000

Walgreens Warrant 2 (2017 Warrants) [Member] | Walgreens Boots Alliance, Inc. [Member] | Investor [Member] | Treasury Stock [Member]

Equity, Class of Treasury Stock [Line Items]

Exercises of warrants

1,157,500,000

Walgreens Warrant 2 (2017 Warrants) [Member] | Walgreens Boots Alliance, Inc. [Member] | Investor [Member] | Additional Paid-in Capital [Member]

Equity, Class of Treasury Stock [Line Items]

Exercises of warrants

$ 34,100,000

August 2013 Share Repurchase Program [Member]

Equity, Class of Treasury Stock [Line Items]

Share repurchase program, authorized amount

$ 750,000,000

Shares repurchased (shares)

1,100,000

Shares repurchased

$ 100,000,000

May 2016 Share Repurchase Program [Member]

Equity, Class of Treasury Stock [Line Items]

Share repurchase program, authorized amount

$ 750,000,000

Shares repurchased (shares)

500,000

4,500,000

2,900,000

2,100,000

Shares repurchased

$ 231,200,000

$ 118,800,000

Accelerated share repurchase program, amount paid

$ 400,000,000

$ 400,000,000

$ 400,000,000

Accelerated share repurchase program, initial funding allocated to shares repurchased

380,000,000

Accelerated share repurchase program, initial funding allocated to share holdback

$ 20,000,000

Settlement of accelerated share repurchase transaction (shares)

500,000

November 2016 Share Repurchase Program [Member]

Equity, Class of Treasury Stock [Line Items]

Share repurchase program, authorized amount

$ 1,000,000,000

Shares repurchased (shares)

7,700,000

2,700,000

Shares repurchased

$ 663,100,000

$ 211,100,000

Share repurchase program, availability remaining

$ 125,800,000

Special Share Repurchase Programs [Member]

Equity, Class of Treasury Stock [Line Items]

Shares repurchased (shares)

26,300,000

18,800,000

Shares repurchased

$ 1,535,100,000

$ 1,774,100,000

Subsequent Event [Member] | November 2016 Share Repurchase Program [Member]

Equity, Class of Treasury Stock [Line Items]

Shares repurchased, cash settled

$ 24,000,000

Subsequent Event [Member] | October 2018 Share Repurchase Program [Member]

Equity, Class of Treasury Stock [Line Items]

Share repurchase program, authorized amount

$ 1,000,000,000

Stockholders' Equity and Weig_4

Stockholders' Equity and Weighted Average Common Shares Outstanding - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ 2,932,824	$ 2,064,461
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(79,253)	(95,850)
Pension and postretirement adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(5,065)	(4,186)
Foreign currency translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(74,811)	(92,164)
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ 623	$ 500

Stockholders' Equity and Weig_5

Stockholders' Equity and Weighted Average Common Shares Outstanding - Components of Diluted Weighted Average Shares Outstanding (Details) - shares shares in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Equity [Abstract]
Weighted average common shares outstanding — basic (shares)	217,872	218,375	212,206
Effect of dilutive securities — stock options, restricted stock, restricted stock units, and the unsettled ASR transaction (shares)	2,464	3,227	3,338
Dilutive effect of the warrants (shares)	0	0	10,415
Weighted average common shares outstanding — diluted (shares)	220,336	221,602	225,959

Related Party Transactions (Det

Related Party Transactions (Details) - Walgreens Boots Alliance, Inc. [Member] - Investor [Member] - USD ($) $ in Billions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Related Party Transaction [Line Items]
Ownership percentage (more than)	10.00%
Revenue from related party	$ 54.7	$ 45.4	$ 43.4
Receivable from related party	$ 5.6	$ 5

Retirement and Other Benefit _2

Retirement and Other Benefit Plans (Details)	1 Months Ended	3 Months Ended	12 Months Ended				24 Months Ended
	Jun. 30, 2016USD ($)	Dec. 31, 2016	Dec. 31, 2019	Sep. 30, 2018USD ($)shares	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2018	Aug. 01, 2014employee
Defined Benefit Plan Disclosure [Line Items]
Number of participants | employee								3,200
Number of active employees | employee								500
Pension settlement				$ 0	$ 0	$ 47,607,000
Expense recognized upon transfer of assets to defined contribution 401(k) plan	$ 17,100,000			$ 0	0	17,149,000
Minimum allowed employee contributions, percent of salary				1.00%
Maximum allowed employee contributions, percent of salary				50.00%
Discretionary contributions					0
Discretionary contributions, vesting period (in years)				5 years
Deferred compensation, annual benefit, percent of compensation, Benefit Restoration Plan		4.00%
Defined contribution plans expense				$ 37,900,000	28,300,000	$ 34,400,000
Deferred compensation, common stock authorized for issuance (shares) | shares				2,960,000
Deferred compensation, common stock issued (shares) | shares				0
Deferred compensation liability				$ 27,500,000	$ 26,300,000
Employee contribution, first 3% of salary [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match		100.00%
Employer matching contribution, percent of salary		3.00%
Employee contribution, additional 2% of salary [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match		50.00%
Employer matching contribution, percent of salary		2.00%
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation, annual benefit, percent of compensation, Benefit Restoration Plan			4.00%				3.00%
Scenario, Forecast [Member] | Employee contribution, first 3% of salary [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match			100.00%				100.00%
Employer matching contribution, percent of salary			3.00%				3.00%
Scenario, Forecast [Member] | Employee contribution, additional 2% of salary [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match			50.00%
Employer matching contribution, percent of salary			2.00%

Share-Based Compensation - Weig

Share-Based Compensation - Weighted Average Assumptions (Details)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	1.89%	1.26%	1.40%
Expected dividend yield	1.96%	1.80%	1.38%
Volatility of common stock	26.54%	26.78%	25.05%
Expected life of the options	3 years 9 months 4 days	3 years 8 months 27 days	3 years 8 months 19 days

Share-Based Compensation - Stoc

Share-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018
Options
Outstanding, beginning of period (shares)			10,287
Granted (shares)			1,538
Exercised (shares)			(2,742)
Forfeited (shares)			(604)
Expired (shares)			(58)
Outstanding, end of period (shares)	8,421	10,287	8,421
Exercisable, end of period (shares)	4,561		4,561
Expected to vest after end of period (shares)	3,732		3,732
Weighted Average Exercise Price
Outstanding, beginning of period (usd per share)			$ 70
Granted (usd per share)			78
Exercised (usd per share)			51
Forfeited (usd per share)			84
Expired (usd per share)			95
Outstanding, end of period (usd per share)	$ 77	$ 70	77
Exercisable, end of period (usd per share)	72		72
Expected to vest after end of period (usd per share)	$ 82		$ 82
Weighted Average Remaining Contractual Term
Outstanding	4 years	4 years
Exercisable	3 years
Expected to vest after end of period	5 years
Aggregate Intrinsic Value
Outstanding	$ 142,557	$ 170,856	$ 142,557
Exercisable	98,863		98,863
Expected to vest after end of period	$ 41,982		$ 41,982

Share-Based Compensation - Nonv

Share-Based Compensation - Nonvested Options (Details) - $ / shares shares in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Options
Nonvested, beginning of period (shares)	4,752
Granted (shares)	1,538
Vested (shares)	(1,826)
Forfeited (shares)	(604)
Nonvested, end of period (shares)	3,860	4,752
Weighted Average Grant Date Fair Value
Nonvested, beginning of period (usd per share)	$ 15
Granted (usd per share)	14.16	$ 13.57	$ 17.43
Vested (usd per share)	14
Forfeited (usd per share)	15
Nonvested, end of period (usd per share)	$ 15	$ 15

Share-Based Compensation - No_2

Share-Based Compensation - Nonvested Restricted Stock Units (Details) - Restricted stock units [Member] shares in Thousands	12 Months Ended
	Sep. 30, 2018$ / sharesshares
Restricted Stock Units
Nonvested, beginning of period (shares) | shares	819
Granted (shares) | shares	526
Vested (shares) | shares	(173)
Forfeited (shares) | shares	(149)
Nonvested, end of period (shares) | shares	1,023
Weighted Average Grant Date Fair Value
Nonvested, beginning of period (usd per share) | $ / shares	$ 84
Granted (usd per share) | $ / shares	78
Vested (usd per share) | $ / shares	91
Forfeited (usd per share) | $ / shares	81
Nonvested, end of period (usd per share) | $ / shares	$ 80

Share-Based Compensation - No_3

Share-Based Compensation - Nonvested Performance Stock Units (Details) - Performance stock units [Member] shares in Thousands	12 Months Ended
	Sep. 30, 2018$ / sharesshares
Performance Stock Units
Nonvested, beginning of period (shares) | shares	201
Granted (shares) | shares	150
Vested (shares) | shares	(80)
Forfeited (shares) | shares	(27)
Nonvested, end of period (shares) | shares	244
Weighted Average Grant Date Fair Value
Nonvested, beginning of period (usd per share) | $ / shares	$ 85
Granted (usd per share) | $ / shares	78
Vested (usd per share) | $ / shares	98
Forfeited (usd per share) | $ / shares	79
Nonvested, end of period (usd per share) | $ / shares	$ 77

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant under plan (shares)	15,600,000	15,600,000		15,600,000
Weighted average fair values of options granted (usd per share)				$ 14.16	$ 13.57	$ 17.43
Stock option expense				$ 22,600,000	$ 28,600,000	$ 33,100,000
Intrinsic value of stock option exercises				116,700,000	116,600,000	120,900,000
Total fair values of options vested				$ 25,800,000	$ 25,200,000	$ 24,400,000
Nonvested options outstanding (shares)	3,860,000	3,860,000		3,860,000	4,752,000
Expected future compensation expense relating to nonvested options outstanding	$ 25,800,000	$ 25,800,000		$ 25,800,000
Weighted average period over which expected future compensation expense relating to nonvested options outstanding will be recognized	2 years 1 month 16 days
ESPP shares authorized (shares)	4,000,000	4,000,000		4,000,000
Requisite service period (in days)				30 days
ESPP, participant election, maximum percent of base salary			25.00%
ESPP, purchase price of stock, percent of fair market value of the stock		85.00%	95.00%
ESPP, stock purchase period (in months)			6 months
ESPP, maximum purchases that can be made during each calendar year by participant				$ 25,000
ESPP, shares acquired from the open market for issuance to participants				72,198	75,904	71,016
Employee discount rate on stock (percentage)		15.00%	5.00%
Employee options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)				4 years
Expiration period (in years)				7 years
Non-employee options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)				3 years
Expiration period (in years)				10 years
Restricted stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)				3 years
Restricted stock expense				$ 26,800,000	$ 25,100,000	$ 19,500,000
Total fair values of restricted shares vested				$ 15,800,000	$ 13,800,000	17,800,000
Nonvested shares outstanding (shares)	1,023,000	1,023,000		1,023,000	819,000
Expected future compensation expense relating to restricted shares outstanding	$ 29,100,000	$ 29,100,000		$ 29,100,000
Weighted average period over which expected future compensation expense relating to restricted shares outstanding will be recognized	1 year 3 months 18 days
Performance stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)				3 years
Nonvested shares outstanding (shares)	244,000	244,000		244,000	201,000
Performance stock unit expense				$ 12,800,000	$ 8,400,000	$ 12,300,000
Performance stock units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				0.00%	0.00%
Performance stock units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				200.00%	150.00%

Leases and Other Commitments -

Leases and Other Commitments - Minimum Lease Payments (Details) $ in Thousands	Sep. 30, 2018USD ($)
Operating Leases
2,019	$ 89,589
2,020	84,689
2,021	75,929
2,022	64,064
2,023	54,168
Thereafter	143,714
Total minimum lease payments	512,153
Financing Obligations
2,019	26,561
2,020	28,137
2,021	27,974
2,022	25,591
2,023	24,401
Thereafter	107,146
Total minimum lease payments	239,810
Operating and Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	116,150
2,020	112,826
2,021	103,903
2,022	89,655
2,023	78,569
Thereafter	250,860
Total minimum lease payments	$ 751,963

Leases and Other Commitments _2

Leases and Other Commitments - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Operating Leases
Rental expense	$ 114.9	$ 80.7	$ 88.8
Other Commitment, Fiscal Year Maturity [Abstract]
Liability related to the transition tax	219.6
Outsourced corporate and information technology activities [Member]
Other Commitment, Fiscal Year Maturity [Abstract]
Remaining commitment	33.7
Remaining commitment, 2019	$ 15

Employee Severance, Litigatio_3

Employee Severance, Litigation, and Other (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Employee severance			$ 36,694	$ 7,767	$ 38,786
Litigation and opioid-related costs		$ 273,400	61,527	917,573	0
Transfer of surplus plan assets	$ 17,100		0	0	17,149
Customer contract dispute settlements			0	0	13,000
Other			85,299	33,987	33,976
Total employee severance, litigation, and other			183,520	959,327	102,911
Other, Acquisition and Integration [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs			33,900	17,000	19,200
Other, Business Transformation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs			33,000	3,700
Other, Other Restructuring Initiatives [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs			$ 18,400	$ 13,300	$ 14,700

Legal Matters and Contingenci_2

Legal Matters and Contingencies (Details) - USD ($) $ in Thousands	Sep. 28, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Loss Contingencies [Line Items]
Litigation settlement					$ 273,400		$ 61,527	$ 917,573	$ 0
Annual fund commitment total			$ 100,000
Estimated liability under the New York Opioid Stewardship Act		$ 22,000
Gain (loss) related to litigation settlement			$ 35,600	$ 300		$ 1,400	35,900	1,400	$ 133,800
USAO-EDNY Misdemeanor Violation [Member]
Loss Contingencies [Line Items]
Litigation settlement								260,000
USAO-EDNY Matter [Member]
Loss Contingencies [Line Items]
Litigation settlement, payment	$ 625,000
Litigation settlement, accrued reserve								625,000
USAO-SDNY Matter [Member]
Loss Contingencies [Line Items]
Litigation settlement								13,400
Litigation settlement, payment							$ 2,800	10,700
West Virginia AG Matter [Member] [Member]
Loss Contingencies [Line Items]
Litigation settlement, payment								16,000
Gain (loss) related to litigation settlement								$ 16,000

Litigation Settlements (Details

Litigation Settlements (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Litigation Settlement [Abstract]
Gain (loss) related to litigation settlement	$ 35.6	$ 0.3	$ 1.4	$ 35.9	$ 1.4	$ 133.8

Business Segment Information -

Business Segment Information - Reconciliation of Segment Revenue, Operating Income, Assets, Depreciation and Amortization, and Capital Expenditures (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenue	$ 43,297,136	$ 43,142,309	$ 41,033,858	$ 40,466,332	$ 39,120,015	$ 38,707,144	$ 37,147,402	$ 38,169,265	$ 167,939,635	$ 153,143,826	$ 146,849,686
Operating income	154,097	$ 389,195	$ 481,420	$ 418,973	(135,002)	$ 170,376	$ 624,981	$ 399,987	1,443,685	1,060,342	1,525,774
Assets	37,669,838				35,316,470				37,669,838	35,316,470	33,637,501
Depreciation and amortization									465,127	397,603	364,735
Capital expenditures									336,411	466,397	464,616
Pharmaceutical Distribution [Member]
Segment Reporting Information [Line Items]
Assets	31,892,621				29,691,127				31,892,621	29,691,127	28,605,047
Capital expenditures									190,191	339,478	359,391
Other [Member]
Segment Reporting Information [Line Items]
Assets	$ 5,777,217				$ 5,625,343				5,777,217	5,625,343	5,032,454
Capital expenditures									146,220	126,919	105,225
Operating segments [Member]
Segment Reporting Information [Line Items]
Operating income									1,981,230	2,016,870	2,030,368
Operating segments [Member] | Pharmaceutical Distribution [Member]
Segment Reporting Information [Line Items]
Revenue									161,699,343	147,453,495	141,701,997
Operating income									1,626,748	1,643,629	1,702,725
Depreciation and amortization									225,608	188,065	170,973
Operating segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenue									6,332,730	5,747,863	5,207,095
Operating income									355,091	373,797	327,746
Depreciation and amortization									64,768	53,160	46,500
Intersegment eliminations [Member]
Segment Reporting Information [Line Items]
Revenue									(92,438)	(57,532)	(59,406)
Operating income									(609)	(556)	(103)
Segment reconciling items [Member]
Segment Reporting Information [Line Items]
Acquisition-related intangibles amortization									$ 174,751	$ 156,378	$ 147,262

Business Segment Information _2

Business Segment Information - Reconciliation of Segment Operating Income to Income From Continuing Operations (Details) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Operating income	$ 154,097,000	$ 389,195,000	$ 481,420,000	$ 418,973,000	$ (135,002,000)	$ 170,376,000	$ 624,981,000	$ 399,987,000	$ 1,443,685,000	$ 1,060,342,000	$ 1,525,774,000
Gain from antitrust litigation settlements		35,600,000	300,000					1,400,000	35,900,000	1,400,000	133,800,000
LIFO (expense) credit	(83,500,000)	16,100,000			$ 74,900,000	$ 24,700,000	$ 86,500,000	$ (28,300,000)	(67,324,000)	157,782,000	(200,230,000)
PharMEDium remediation costs	(26,600,000)	(12,000,000)	(22,500,000)
Warrants expense									0	0	(140,342,000)
Employee severance, litigation, and other									(183,520,000)	(959,327,000)	(102,911,000)
Pension settlement charge									0	0	(47,607,000)
Goodwill impairment	$ (59,684,000)	$ 0	$ 0	0					(59,684,000)	0	0
Other loss (income)									25,469,000	(2,730,000)	(5,048,000)
Interest expense, net									174,699,000	145,185,000	139,912,000
Loss on consolidation of equity investments									42,328,000	0	0
Loss on early retirement of debt				$ (23,800,000)					23,766,000	0	0
Income before income taxes									1,177,423,000	917,887,000	1,390,910,000
Operating segments [Member]
Segment Reporting Information [Line Items]
Operating income									1,981,230,000	2,016,870,000	2,030,368,000
Segment reconciling items [Member]
Segment Reporting Information [Line Items]
Gain from antitrust litigation settlements									35,938,000	1,395,000	133,758,000
LIFO (expense) credit									(67,324,000)	157,782,000	(200,230,000)
PharMEDium remediation costs									(66,204,000)	0	0
New York State Opioid Stewardship Act									(22,000,000)	0	0
Acquisition-related intangibles amortization									(174,751,000)	(156,378,000)	(147,262,000)
Warrants expense									0	0	(140,342,000)
Employee severance, litigation, and other									(183,520,000)	(959,327,000)	(102,911,000)
Pension settlement charge									0	0	(47,607,000)
Goodwill impairment									$ (59,684,000)	$ 0	$ 0

Business Segment Information _3

Business Segment Information - Additional Information (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2018USD ($)country	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Segment Reporting Information [Line Items]
Impairment of non-customer note receivable	$ 30,000	$ 0	$ 0
Other Segments [Member] | World Courier [Member]
Segment Reporting Information [Line Items]
Number of countries in which entity operates (over) | country	50
Other Nonoperating Income (Expense) [Member]
Segment Reporting Information [Line Items]
Impairment of non-customer note receivable	$ 30,000

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Fair value [Member] | Level 1 [Member] | Money market accounts [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	$ 1,050	$ 800
Fair value [Member] | Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Long-term debt	4,000.1	3,522.5
Carrying amount [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Long-term debt	$ 4,158.5	$ 3,429.9

Quarterly Financial Informati_3

Quarterly Financial Information (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Loss Contingencies [Line Items]
Revenue	$ 43,297,136,000	$ 43,142,309,000	$ 41,033,858,000	$ 40,466,332,000	$ 39,120,015,000	$ 38,707,144,000	$ 37,147,402,000	$ 38,169,265,000	$ 167,939,635,000	$ 153,143,826,000	$ 146,849,686,000
Gross profit	1,032,641,000	1,211,341,000	1,255,683,000	1,112,652,000	1,172,020,000	1,079,875,000	1,256,427,000	1,037,680,000	4,612,317,000	4,546,002,000	4,272,606,000
Distribution, selling, and administrative expenses; depreciation; and amortization	778,363,000	746,593,000	736,814,000	663,658,000	665,212,000	624,982,000	619,512,000	616,627,000	2,925,428,000	2,526,333,000
Employee severance, litigation, and other	40,497,000	75,553,000	37,449,000	30,021,000	641,810,000	284,517,000	11,934,000	21,066,000	183,520,000	959,327,000
Goodwill impairment	59,684,000	0	0	0					59,684,000	0	0
Operating income	154,097,000	389,195,000	481,420,000	418,973,000	(135,002,000)	170,376,000	624,981,000	399,987,000	1,443,685,000	1,060,342,000	1,525,774,000
Net income (loss)	194,004,000	277,875,000	282,160,000	861,853,000					1,615,892,000	364,484,000	1,427,929,000
Net income attributable to AmerisourceBergen Corporation	$ 233,288,000	$ 275,809,000	$ 287,455,000	$ 861,853,000	$ (344,587,000)	$ 50,352,000	$ 411,473,000	$ 247,246,000	$ 1,658,405,000	$ 364,484,000	$ 1,427,929,000
Earnings per share operations:
Basic (usd per share)	$ 1.08	$ 1.26	$ 1.31	$ 3.95	$ (1.58)	$ 0.23	$ 1.89	$ 1.13	$ 7.61	$ 1.67	$ 6.73
Diluted (usd per share)	$ 1.07	$ 1.25	$ 1.29	$ 3.90	$ (1.58)	$ 0.23	$ 1.86	$ 1.11	$ 7.53	$ 1.64	$ 6.32
Gain (loss) related to litigation settlement		$ 35,600,000	$ 300,000					$ 1,400,000	$ 35,900,000	$ 1,400,000	$ 133,800,000
LIFO charges (credit)	$ 83,500,000	(16,100,000)			$ (74,900,000)	$ (24,700,000)	$ (86,500,000)	$ 28,300,000	67,324,000	(157,782,000)	200,230,000
PharMEDium remediation costs	26,600,000	$ 12,000,000	22,500,000
Estimated liability under the New York Opioid Stewardship Act	22,000,000
Loss on early retirement of debt				$ 23,800,000					(23,766,000)	0	0
Impairment charge on equity investment			42,300,000
Impairment of non-customer note receivable			$ 30,000,000
Discrete income tax benefits recognized in connection with 2017 Tax Act	$ 25,000,000			$ 587,600,000					612,600,000
Litigation settlements						$ 273,400,000			$ 61,527,000	917,573,000	$ 0
USAO-EDNY Matter [Member]
Earnings per share operations:
Litigation settlement, accrued reserve										$ 625,000,000

Subsequent Event (Details)

Subsequent Event (Details) - Subsequent Event [Member]	1 Months Ended
	Nov. 30, 2018$ / shares
Subsequent Event [Line Items]
Dividend increase percentage	5.00%
Quarterly cash dividend declared (usd per share)	$ 0.40

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Details) - Allowances for returns and doubtful accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 1,068,251	$ 926,034	$ 923,755
Charged to Costs and Expenses	3,397,562	3,157,960	2,882,914
Deductions	(3,415,912)	(3,015,743)	(2,880,635)
Balance at End of Period	$ 1,049,901	$ 1,068,251	$ 926,034

Schedule II - Valuation and Q_3

Schedule II - Valuation and Qualifying Accounts - Additional Information (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Allowance for Doubtful Accounts for Long-term Accounts Receivable [Member] | Other Assets [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts for long-term accounts receivable	$ 13,568	$ 17,890	$ 20,689