Merck & Co. (MRK) 10-K 27 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	MRK
Entity Registrant Name	Merck & Co., Inc.
Entity Central Index Key	310,158
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		2,581,220,308
Entity Public Float			$ 161,991

Consolidated Statement of Incom

Consolidated Statement of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Sales	$ 42,294	$ 40,122	$ 39,807
Costs, Expenses and Other
Cost of sales	13,509	12,912	14,030
Selling, general and administrative	10,102	10,074	10,017
Research and development	9,752	10,339	10,261
Restructuring costs	632	776	651
Other (income) expense, net	(402)	(500)	189
Total Costs, Expenses and Other	33,593	33,601	35,148
Income Before Taxes	8,701	6,521	4,659
Taxes on Income	2,508	4,103	718
Net Income	6,193	2,418	3,941
Less: Net (Loss) Income Attributable to Noncontrolling Interests	(27)	24	21
Net Income Attributable to Merck & Co., Inc.	$ 6,220	$ 2,394	$ 3,920
Basic Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 2.34	$ 0.88	$ 1.42
Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 2.32	$ 0.87	$ 1.41

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net Income Attributable to Merck & Co., Inc.	$ 6,220	$ 2,394	$ 3,920
Other Comprehensive (Loss) Income Net of Taxes:
Net unrealized gain (loss) on derivatives, net of reclassifications	297	(446)	(66)
Net unrealized loss on investments, net of reclassifications	(10)	(58)	(44)
Benefit plan net (loss) gain and prior service (cost) credit, net of amortization	(425)	419	(799)
Cumulative translation adjustment	(223)	401	(169)
Other comprehensive income (loss), net of taxes	(361)	316	(1,078)
Comprehensive Income Attributable to Merck & Co., Inc.	$ 5,859	$ 2,710	$ 2,842

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Current Assets
Cash and cash equivalents	$ 7,965	$ 6,092
Short-term investments	899	2,406
Accounts receivable (net of allowance for doubtful accounts of $119 in 2018 and $159 in 2017)	7,071	6,873
Inventories (excludes inventories of $1,417 in 2018 and $1,187 in 2017 classified in Other assets - see Note 7)	5,440	5,096
Other current assets	4,500	4,299
Total current assets	25,875	24,766
Investments	6,233	12,125
Property, Plant and Equipment (at cost)
Land	333	365
Buildings	11,486	11,726
Machinery, equipment and office furnishings	14,441	14,649
Construction in progress	3,355	2,301
Property, plant and equipment (at cost)	29,615	29,041
Less: accumulated depreciation	16,324	16,602
Property, plant and equipment, net	13,291	12,439
Goodwill	18,253	18,284
Other Intangibles, Net	11,431	14,183
Other Assets	7,554	6,075
Total Assets	82,637	87,872
Current Liabilities
Loans payable and current portion of long-term debt	5,308	3,057
Trade accounts payable	3,318	3,102
Accrued and other current liabilities	10,151	10,427
Income taxes payable	1,971	708
Dividends payable	1,458	1,320
Total current liabilities	22,206	18,614
Long-Term Debt	19,806	21,353
Deferred Income Taxes	1,702	2,219
Other Noncurrent Liabilities	12,041	11,117
Merck & Co., Inc. Stockholders’ Equity
Common stock, $0.50 par value Authorized - 6,500,000,000 shares Issued - 3,577,103,522 shares in 2018 and 2017	1,788	1,788
Other paid-in capital	38,808	39,902
Retained earnings	42,579	41,350
Accumulated other comprehensive loss	(5,545)	(4,910)
Stockholders' equity before deduction for treasury stock	77,630	78,130
Less treasury stock, at cost: 984,543,979 shares in 2018 and 880,491,914 shares in 2017	50,929	43,794
Total Merck & Co., Inc. stockholders’ equity	26,701	34,336
Noncontrolling Interests	181	233
Total equity	26,882	34,569
Total Liabilities and Equity	$ 82,637	$ 87,872

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 119	$ 159
Inventories classified in other assets	$ 1,417	$ 1,187
Common stock, par value (in dollars per share)	$ 0.50	$ 0.50
Common stock, shares authorized (in shares)	6,500,000,000	6,500,000,000
Common stock, shares issued (in shares)	3,577,103,522	3,577,103,522
Treasury stock, shares (in shares)	984,543,979	880,491,914

Consolidated Statement of Equit

Consolidated Statement of Equity - USD ($) $ in Millions	Total	The StayWell Company LLC	Vallee S.A.	Common Stock	Other Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	Non- controlling Interests	Non- controlling InterestsThe StayWell Company LLC	Non- controlling InterestsVallee S.A.
Beginning Balance at Dec. 31, 2015	$ 44,767			$ 1,788	$ 40,222	$ 45,348	$ (4,148)	$ (38,534)	$ 91
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income Attributable to Merck & Co., Inc.	3,920					3,920
Other comprehensive income (loss), net of taxes	(1,078)						(1,078)
Cash dividends declared on common stock (1.99 per share in 2018, $1.89 per share in 2017 and $1.85 per share in 2016)	(5,135)					(5,135)
Treasury stock shares purchased	(3,434)							(3,434)
Acquisition		$ 124								$ 124
Net loss attributable to noncontrolling interests	21								21
Distributions attributable to noncontrolling interests	(16)								(16)
Share-based compensation plans and other	1,139				(283)			1,422
Ending Balance at Dec. 31, 2016	40,308			1,788	39,939	44,133	(5,226)	(40,546)	220
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income Attributable to Merck & Co., Inc.	2,394					2,394
Other comprehensive income (loss), net of taxes	316						316
Cash dividends declared on common stock (1.99 per share in 2018, $1.89 per share in 2017 and $1.85 per share in 2016)	(5,177)					(5,177)
Treasury stock shares purchased	(4,014)							(4,014)
Acquisition			$ 7								$ 7
Net loss attributable to noncontrolling interests	24								24
Distributions attributable to noncontrolling interests	(18)								(18)
Share-based compensation plans and other	729				(37)			766
Ending Balance at Dec. 31, 2017	34,569			1,788	39,902	41,350	(4,910)	(43,794)	233
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income Attributable to Merck & Co., Inc.	6,220					6,220
Other comprehensive income (loss), net of taxes	(361)						(361)
Cash dividends declared on common stock (1.99 per share in 2018, $1.89 per share in 2017 and $1.85 per share in 2016)	(5,313)					(5,313)
Treasury stock shares purchased	(9,091)				(1,000)			(8,091)
Net loss attributable to noncontrolling interests	(27)								(27)
Distributions attributable to noncontrolling interests	(25)								(25)
Share-based compensation plans and other	862				(94)			956
Ending Balance at Dec. 31, 2018	26,882			$ 1,788	$ 38,808	42,579	(5,545)	$ (50,929)	$ 181
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards (see Note 2)	$ 48					$ 322	$ (274)

Consolidated Statement of Equ_2

Consolidated Statement of Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Common stock, dividends declared (in dollars per share)	$ 1.99	$ 1.89	$ 1.85

Consolidated Statement of Cash

Consolidated Statement of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows from Operating Activities
Net income	$ 6,193	$ 2,418	$ 3,941
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	4,519	4,676	5,471
Intangible asset impairment charges	296	646	3,948
Charge for future payments related to collaboration license options	650	500	0
Provisional charge for one-time transition tax related to the enactment of U.S. tax legislation	0	5,347	0
Charge related to the settlement of worldwide Keytruda patent litigation	0	0	625
Deferred income taxes	(509)	(2,621)	(1,521)
Share-based compensation	348	312	300
Other	978	190	213
Net changes in assets and liabilities:
Accounts receivable	(418)	297	(619)
Inventories	(911)	(145)	206
Trade accounts payable	230	254	278
Accrued and other current liabilities	(341)	(922)	(2,018)
Income taxes payable	827	(3,291)	124
Noncurrent liabilities	(266)	(123)	(809)
Other	(674)	(1,087)	237
Net Cash Provided by Operating Activities	10,922	6,451	10,376
Cash Flows from Investing Activities
Capital expenditures	(2,615)	(1,888)	(1,614)
Purchases of securities and other investments	(7,994)	(10,739)	(15,651)
Proceeds from sales of securities and other investments	15,252	15,664	14,353
Acquisitions, net of cash acquired	(431)	(396)	(780)
Other	102	38	482
Net Cash Provided by (Used in) Investing Activities	4,314	2,679	(3,210)
Cash Flows from Financing Activities
Net change in short-term borrowings	5,124	(26)	0
Payments on debt	(4,287)	(1,103)	(2,386)
Proceeds from issuance of debt	0	0	1,079
Purchases of treasury stock	(9,091)	(4,014)	(3,434)
Dividends paid to stockholders	(5,172)	(5,167)	(5,124)
Proceeds from exercise of stock options	591	499	939
Other	(325)	(195)	(118)
Net Cash Used in Financing Activities	(13,160)	(10,006)	(9,044)
Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	(205)	457	(131)
Net Increase (Decrease) in Cash, Cash Equivalents and Restricted Cash	1,871	(419)	(2,009)
Cash, Cash Equivalents and Restricted Cash at Beginning of Year (includes $4 million of restricted cash at January 1, 2018 included in Other Assets)	6,096	6,515	8,524
Cash, Cash Equivalents and Restricted Cash at End of Year (includes $2 million of restricted cash at December 31, 2018 included in Other Assets)	$ 7,967	$ 6,096	$ 6,515

Consolidated Statement of Cas_2

Consolidated Statement of Cash Flows (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Statement of Cash Flows [Abstract]
Restricted Cash	$ 2	$ 4

Nature of Operations

Nature of Operations	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations Merck & Co., Inc. (Merck or the Company) is a global health care company that delivers innovative health solutions through its prescription medicines, vaccines, biologic therapies and animal health products. The Company’s operations are principally managed on a products basis and include four operating segments, which are the Pharmaceutical, Animal Health, Healthcare Services and Alliances segments. The Pharmaceutical and Animal Health segments are the only reportable segments. The Pharmaceutical segment includes human health pharmaceutical and vaccine products. Human health pharmaceutical products consist of therapeutic and preventive agents, generally sold by prescription, for the treatment of human disorders. The Company sells these human health pharmaceutical products primarily to drug wholesalers and retailers, hospitals, government agencies and managed health care providers such as health maintenance organizations, pharmacy benefit managers and other institutions. Human health vaccine products consist of preventive pediatric, adolescent and adult vaccines, primarily administered at physician offices. The Company sells these human health vaccines primarily to physicians, wholesalers, physician distributors and government entities. On December 31, 2016, Merck and Sanofi Pasteur S.A. (Sanofi) terminated their equally-owned joint venture, Sanofi Pasteur MSD (SPMSD), which developed and marketed vaccines in Europe. In 2017, Merck began recording vaccine sales and incurring costs as a result of operating its vaccines business in the European markets that were previously part of the SPMSD joint venture, which was accounted for as an equity method affiliate. The Animal Health segment discovers, develops, manufactures and markets animal health products, including pharmaceutical and vaccine products, for the prevention, treatment and control of disease in all major livestock and companion animal species, which the Company sells to veterinarians, distributors and animal producers. The Healthcare Services segment provides services and solutions that focus on engagement, health analytics and clinical services to improve the value of care delivered to patients. The Alliances segment primarily includes activity from the Company’s relationship with AstraZeneca LP related to sales of Nexium and Prilosec, which concluded in 2018 (see Note 9).

Summary of Accounting Policies

Summary of Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Accounting Policies	Summary of Accounting Policies Principles of Consolidation — The consolidated financial statements include the accounts of the Company and all of its subsidiaries in which a controlling interest is maintained. Intercompany balances and transactions are eliminated. Controlling interest is determined by majority ownership interest and the absence of substantive third-party participating rights or, in the case of variable interest entities, by majority exposure to expected losses, residual returns or both. For those consolidated subsidiaries where Merck ownership is less than 100%, the outside shareholders’ interests are shown as Noncontrolling interests in equity. Investments in affiliates over which the Company has significant influence but not a controlling interest, such as interests in entities owned equally by the Company and a third party that are under shared control, are carried on the equity basis. Acquisitions — In a business combination, the acquisition method of accounting requires that the assets acquired and liabilities assumed be recorded as of the date of the acquisition at their respective fair values with limited exceptions. Assets acquired and liabilities assumed in a business combination that arise from contingencies are generally recognized at fair value. If fair value cannot be determined, the asset or liability is recognized if probable and reasonably estimable; if these criteria are not met, no asset or liability is recognized. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Accordingly, the Company may be required to value assets at fair value measures that do not reflect the Company’s intended use of those assets. Any excess of the purchase price (consideration transferred) over the estimated fair values of net assets acquired is recorded as goodwill. Transaction costs and costs to restructure the acquired company are expensed as incurred. The operating results of the acquired business are reflected in the Company’s consolidated financial statements after the date of the acquisition. If the Company determines the assets acquired do not meet the definition of a business under the acquisition method of accounting, the transaction will be accounted for as an acquisition of assets rather than a business combination and, therefore, no goodwill will be recorded. In an asset acquisition, acquired in-process research and development (IPR&D) with no alternative future use is charged to expense and contingent consideration is not recognized at the acquisition date. Foreign Currency Translation — The net assets of international subsidiaries where the local currencies have been determined to be the functional currencies are translated into U.S. dollars using current exchange rates. The U.S. dollar effects that arise from translating the net assets of these subsidiaries at changing rates are recorded in the foreign currency translation account, which is included in Accumulated other comprehensive income (loss) ( AOCI ) and reflected as a separate component of equity. For those subsidiaries that operate in highly inflationary economies and for those subsidiaries where the U.S. dollar has been determined to be the functional currency, non-monetary foreign currency assets and liabilities are translated using historical rates, while monetary assets and liabilities are translated at current rates, with the U.S. dollar effects of rate changes included in Other (income) expense, net . Cash Equivalents — Cash equivalents are comprised of certain highly liquid investments with original maturities of less than three months. Inventories — Inventories are valued at the lower of cost or net realizable value. The cost of a substantial majority of U.S. pharmaceutical and vaccine inventories is determined using the last-in, first-out (LIFO) method for both financial reporting and tax purposes. The cost of all other inventories is determined using the first-in, first-out (FIFO) method. Inventories consist of currently marketed products, as well as certain inventories produced in preparation for product launches that are considered to have a high probability of regulatory approval. In evaluating the recoverability of inventories produced in preparation for product launches, the Company considers the likelihood that revenue will be obtained from the future sale of the related inventory together with the status of the product within the regulatory approval process. Investments — Investments in marketable debt securities classified as available-for-sale are reported at fair value. Fair values of the Company’s investments in marketable debt securities are determined using quoted market prices in active markets for identical assets or liabilities or quoted prices for similar assets or liabilities or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Changes in fair value that are considered temporary are reported net of tax in Other Comprehensive Income ( OCI ). The Company considers available evidence in evaluating potential impairments of its investments in marketable debt securities, including the duration and extent to which fair value is less than cost. An other-than-temporary impairment has occurred if the Company does not expect to recover the entire amortized cost basis of the marketable debt security. If the Company does not intend to sell the impaired debt security, and it is not more likely than not it will be required to sell the debt security before the recovery of its amortized cost basis, the amount of the other-than-temporary impairment recognized in earnings, recorded in Other (income) expense, net , is limited to the portion attributed to credit loss. The remaining portion of the other-than-temporary impairment related to other factors is recognized in OCI . Realized gains and losses for debt securities are included in Other (income) expense, net . Investments in publicly traded equity securities are reported at fair value determined using quoted market prices in active markets for identical assets or quoted prices for similar assets or other inputs that are observable or can be corroborated by observable market data. Changes in fair value are included in Other (income) expense, net . Investments in equity securities without readily determinable fair values are recorded at cost, plus or minus subsequent observable price changes in orderly transactions for identical or similar investments, minus impairments. Such adjustments are recognized in Other (income) expense, net . Realized gains and losses for equity securities are included in Other (income) expense, net . Revenue Recognition — On January 1, 2018, the Company adopted ASU 2014-09, Revenue from Contracts with Customers , and subsequent amendments (ASC 606 or new guidance), using the modified retrospective method. Merck applied the new guidance to all contracts with customers within the scope of the standard that were in effect on January 1, 2018 and recognized the cumulative effect of initially applying the new guidance as an adjustment to the opening balance of retained earnings (see “ Recently Adopted Accounting Standards ” below). Comparative information for prior periods has not been restated and continues to be reported under the accounting standards in effect for those periods. The new guidance requires an entity to recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration that it expects to be entitled to in exchange for those goods or services. The new guidance introduces a 5-step model to recognize revenue when or as control is transferred: identify the contract with a customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when or as the performance obligations are satisfied. Changes to the Company’s revenue recognition policy as a result of adopting ASC 606 are described below. See Note 19 for disaggregated revenue disclosures. Recognition of revenue requires evidence of a contract, probable collection of sales proceeds and completion of substantially all performance obligations. Merck acts as the principal in substantially all of its customer arrangements and therefore records revenue on a gross basis. The majority of the Company’s contracts related to the Pharmaceutical and Animal Health segments have a single performance obligation - the promise to transfer goods. Shipping is considered immaterial in the context of the overall customer arrangement and damages or loss of goods in transit are rare. Therefore, shipping is not deemed a separately recognized performance obligation. The vast majority of revenues from sales of products are recognized at a point in time when control of the goods is transferred to the customer, which the Company has determined is when title and risks and rewards of ownership transfer to the customer and the Company is entitled to payment. Certain Merck entities, including U.S. entities, have contract terms under which control of the goods passes to the customer upon shipment; however, either pursuant to the terms of the contract or as a business practice, Merck retains responsibility for goods lost or damaged in transit. Prior to the adoption of the new standard, Merck would recognize revenue for these entities upon delivery of the goods. Under the new guidance, the Company is now recognizing revenue at time of shipment for these entities. The Company recognizes revenue from the sales of vaccines to the Federal government for placement into vaccine stockpiles in accordance with Securities and Exchange Commission (SEC) Interpretation , Commission Guidance Regarding Accounting for Sales of Vaccines and BioTerror Countermeasures to the Federal Government for Placement into the Pediatric Vaccine Stockpile or the Strategic National Stockpile . This interpretation allows companies to recognize revenue for sales of vaccines into U.S. government stockpiles even though these sales might not meet the criteria for revenue recognition under other accounting guidance. For businesses within the Company’s Healthcare Services segment and certain services in the Animal Health segment, revenue is recognized over time, generally ratably over the contract term as services are provided. These service revenues are not material. The nature of the Company’s business gives rise to several types of variable consideration including discounts and returns, which are estimated at the time of sale generally using the expected value method, although the most likely amount method is used for prompt pay discounts. In the United States, sales discounts are issued to customers at the point-of-sale, through an intermediary wholesaler (known as chargebacks), or in the form of rebates. Additionally, sales are generally made with a limited right of return under certain conditions. Revenues are recorded net of provisions for sales discounts and returns, which are established at the time of sale. In addition, revenues are recorded net of time value of money discounts if collection of accounts receivable is expected to be in excess of one year. The U.S. provision for aggregate customer discounts covering chargebacks and rebates was $10.7 billion in 2018, $10.7 billion in 2017 and $9.7 billion in 2016. Chargebacks are discounts that occur when a contracted customer purchases through an intermediary wholesaler. The contracted customer generally purchases product from the wholesaler at its contracted price plus a mark-up. The wholesaler, in turn, charges the Company back for the difference between the price initially paid by the wholesaler and the contract price paid to the wholesaler by the customer. The provision for chargebacks is based on expected sell-through levels by the Company’s wholesale customers to contracted customers, as well as estimated wholesaler inventory levels. Rebates are amounts owed based upon definitive contractual agreements or legal requirements with private sector and public sector (Medicaid and Medicare Part D) benefit providers, after the final dispensing of the product by a pharmacy to a benefit plan participant. The provision for rebates is based on expected patient usage, as well as inventory levels in the distribution channel to determine the contractual obligation to the benefit providers. The Company uses historical customer segment utilization mix, sales forecasts, changes to product mix and price, inventory levels in the distribution channel, government pricing calculations and prior payment history in order to estimate the expected provision. Amounts accrued for aggregate customer discounts are evaluated on a quarterly basis through comparison of information provided by the wholesalers, health maintenance organizations, pharmacy benefit managers, federal and state agencies, and other customers to the amounts accrued. The accrued balances relative to the provisions for chargebacks and rebates included in Accounts receivable and Accrued and other current liabilities were $245 million and $2.4 billion , respectively, at December 31, 2018 and were $198 million and $2.4 billion , respectively, at December 31, 2017 . Outside of the United States, variable consideration in the form of discounts and rebates are a combination of commercially-driven discounts in highly competitive product classes, discounts required to gain or maintain reimbursement, or legislatively mandated rebates. In certain European countries, legislatively mandated rebates are calculated based on an estimate of the government’s total unbudgeted spending and the Company’s specific payback obligation. Rebates may also be required based on specific product sales thresholds. The Company applies an estimated factor against its actual invoiced sales to represent the expected level of future discount or rebate obligations associated with the sale. The Company maintains a returns policy that allows its U.S. pharmaceutical customers to return product within a specified period prior to and subsequent to the expiration date (generally, three to six months before and 12 months after product expiration). The estimate of the provision for returns is based upon historical experience with actual returns. Additionally, the Company considers factors such as levels of inventory in the distribution channel, product dating and expiration period, whether products have been discontinued, entrance in the market of generic competition, changes in formularies or launch of over-the-counter products, among others. Outside of the United States, returns are only allowed in certain countries on a limited basis. Merck’s payment terms for U.S. pharmaceutical customers are typically net 36 days from receipt of invoice and for U.S. animal health customers are typically net 30 days from receipt of invoice; however, certain products, including Keytruda , have longer payment terms up to 90 days. Outside of the United States, payment terms are typically 30 days to 90 days, although certain markets have longer payment terms. The following table provides the effects of adopting ASC 606 on the Consolidated Statement of Income: Year Ended December 31, 2018 As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Sales $ 42,294 $ (2 ) $ 42,292 Cost of sales 13,509 (6 ) 13,503 Income before taxes 8,701 4 8,705 Taxes on income 2,508 1 2,509 Net income attributable to Merck & Co., Inc. 6,220 3 6,223 The following table provides the effects of adopting ASC 606 on the Consolidated Balance Sheet: December 31, 2018 As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Assets Accounts receivable $ 7,071 $ (13 ) $ 7,058 Inventories 5,440 7 5,447 Liabilities Accrued and other current liabilities 10,151 (3 ) 10,148 Income taxes payable 1,971 (1 ) 1,970 Equity Retained earnings 42,579 (2 ) 42,577 Depreciation — Depreciation is provided over the estimated useful lives of the assets, principally using the straight-line method. For tax purposes, accelerated tax methods are used. The estimated useful lives primarily range from 25 to 45 years for Buildings , and from 3 to 15 years for Machinery, equipment and office furnishings . Depreciation expense was $1.4 billion in 2018 , $1.5 billion in 2017 and $1.6 billion in 2016 . Advertising and Promotion Costs — Advertising and promotion costs are expensed as incurred. The Company recorded advertising and promotion expenses of $2.1 billion , $2.2 billion and $2.1 billion in 2018 , 2017 and 2016 , respectively. Software Capitalization — The Company capitalizes certain costs incurred in connection with obtaining or developing internal-use software including external direct costs of material and services, and payroll costs for employees directly involved with the software development. Capitalized software costs are included in Property, plant and equipment and amortized beginning when the software project is substantially complete and the asset is ready for its intended use. Capitalized software costs associated with projects that are being amortized over 6 to 10 years (including the Company’s on-going multi-year implementation of an enterprise-wide resource planning system) were $439 million and $449 million , net of accumulated amortization at December 31, 2018 and 2017 , respectively. All other capitalized software costs are being amortized over periods ranging from 3 to 5 years. Costs incurred during the preliminary project stage and post-implementation stage, as well as maintenance and training costs, are expensed as incurred. Goodwill — Goodwill represents the excess of the consideration transferred over the fair value of net assets of businesses acquired. Goodwill is assigned to reporting units and evaluated for impairment on at least an annual basis, or more frequently if impairment indicators exist, by first assessing qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If the Company concludes it is more likely than not that the fair value of a reporting unit is less than its carrying amount, a quantitative fair value test is performed. If the carrying value of a reporting unit is greater than its fair value, a goodwill impairment charge will be recorded for the difference (up to the carrying value of goodwill). Acquired Intangibles — Acquired intangibles include products and product rights, tradenames and patents, which are initially recorded at fair value, assigned an estimated useful life, and amortized primarily on a straight-line basis over their estimated useful lives ranging from 2 to 20 years (see Note 8). The Company periodically evaluates whether current facts or circumstances indicate that the carrying values of its acquired intangibles may not be recoverable. If such circumstances are determined to exist, an estimate of the undiscounted future cash flows of these assets, or appropriate asset groupings, is compared to the carrying value to determine whether an impairment exists. If the asset is determined to be impaired, the loss is measured based on the difference between the carrying value of the intangible asset and its fair value, which is determined based on the net present value of estimated future cash flows. Acquired In-Process Research and Development — Acquired IPR&D that the Company acquires through business combinations represents the fair value assigned to incomplete research projects which, at the time of acquisition, have not reached technological feasibility. The amounts are capitalized and are accounted for as indefinite-lived intangible assets, subject to impairment testing until completion or abandonment of the projects. Upon successful completion of each project, Merck will make a determination as to the then-useful life of the intangible asset, generally determined by the period in which the substantial majority of the cash flows are expected to be generated, and begin amortization. The Company tests IPR&D for impairment at least annually, or more frequently if impairment indicators exist, by first assessing qualitative factors to determine whether it is more likely than not that the fair value of the IPR&D intangible asset is less than its carrying amount. If the Company concludes it is more likely than not that the fair value is less than the carrying amount, a quantitative test that compares the fair value of the IPR&D intangible asset with its carrying value is performed. If the fair value is less than the carrying amount, an impairment loss is recognized in operating results. Contingent Consideration — Certain of the Company’s business acquisitions involve the potential for future payment of consideration that is contingent upon the achievement of performance milestones, including product development milestones and royalty payments on future product sales. The fair value of contingent consideration liabilities is determined at the acquisition date using unobservable inputs. These inputs include the estimated amount and timing of projected cash flows, the probability of success (achievement of the contingent event) and the risk-adjusted discount rate used to present value the probability-weighted cash flows. Subsequent to the acquisition date, at each reporting period, the contingent consideration liability is remeasured at current fair value with changes (either expense or income) recorded in earnings. Research and Development — Research and development is expensed as incurred. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. Research and development expenses include restructuring costs and IPR&D impairment charges. In addition, research and development expenses include expense or income related to changes in the estimated fair value measurement of liabilities for contingent consideration. Research and development expenses also include upfront and milestone payments related to asset acquisitions and licensing transactions involving clinical development programs that have not yet received regulatory approval. Collaborative Arrangements — Merck has entered into collaborative arrangements that provide the Company with varying rights to develop, produce and market products together with its collaborative partners. When Merck is the principal on sales transactions with third parties, the Company recognizes sales, cost of sales and selling, general and administrative expenses on a gross basis. Profit sharing amounts it pays to its collaborative partners are recorded within Cost of sales . When the collaborative partner is the principal on sales transactions with third parties, the Company records profit sharing amounts received from its collaborative partners as alliance revenue (within Sales ). Alliance revenue is recorded net of cost of sales and includes an adjustment to share commercialization costs between the partners in accordance with the collaboration agreement. The adjustment is determined by comparing the commercialization costs Merck has incurred directly and reported within Selling, general and administrative expenses with the costs the collaborative partner has incurred. Research and development costs Merck incurs related to collaborations are recorded within Research and development expenses. Cost reimbursements to the collaborative partner or payments received from the collaborative partner to share these costs pursuant to the terms of the collaboration agreements are recorded as increases or decreases to Research and development expenses. In addition, the terms of the collaboration agreements may require the Company to make payments based upon the achievement of certain developmental, regulatory approval or commercial milestones. Upfront and milestone payments payable by Merck to collaborative partners prior to regulatory approval are expensed as incurred and included in Research and development expenses. Payments due to collaborative partners upon or subsequent to regulatory approval are capitalized and amortized over the estimated useful life of the corresponding intangible asset to Cost of sales provided that future cash flows support the amounts capitalized. Sales-based milestones payable by Merck to collaborative partners are accrued when probable of being achieved and capitalized, subject to cumulative amortization catch-up. The amortization catch-up is calculated either from the time of the first regulatory approval for indications that were unapproved at the time the collaboration was formed, or from time of the formation of the collaboration for approved products. The related intangible asset that is recognized is amortized to Cost of sales over its remaining useful life, subject to impairment testing. Share-Based Compensation — The Company expenses all share-based payments to employees over the requisite service period based on the grant-date fair value of the awards. Restructuring Costs — The Company records liabilities for costs associated with exit or disposal activities in the period in which the liability is incurred. In accordance with existing benefit arrangements, employee termination costs are accrued when the restructuring actions are probable and estimable. When accruing these costs, the Company will recognize the amount within a range of costs that is the best estimate within the range. When no amount within the range is a better estimate than any other amount, the Company recognizes the minimum amount within the range. Costs for one-time termination benefits in which the employee is required to render service until termination in order to receive the benefits are recognized ratably over the future service period. Contingencies and Legal Defense Costs — The Company records accruals for contingencies and legal defense costs expected to be incurred in connection with a loss contingency when it is probable that a liability has been incurred and the amount can be reasonably estimated. Taxes on Income — Deferred taxes are recognized for the future tax effects of temporary differences between financial and income tax reporting based on enacted tax laws and rates. The Company evaluates tax positions to determine whether the benefits of tax positions are more likely than not of being sustained upon audit based on the technical merits of the tax position. For tax positions that are more likely than not of being sustained upon audit, the Company recognizes the largest amount of the benefit that is greater than 50% likely of being realized upon ultimate settlement in the financial statements. For tax positions that are not more likely than not of being sustained upon audit, the Company does not recognize any portion of the benefit in the financial statements. The Company recognizes interest and penalties associated with uncertain tax positions as a component of Taxes on income in the Consolidated Statement of Income. Use of Estimates — The consolidated financial statements are prepared in conformity with accounting principles generally accepted in the United States (GAAP) and, accordingly, include certain amounts that are based on management’s best estimates and judgments. Estimates are used when accounting for amounts recorded in connection with acquisitions, including initial fair value determinations of assets and liabilities, primarily IPR&D, other intangible assets and contingent consideration, as well as subsequent fair value measurements. Additionally, estimates are used in determining such items as provisions for sales discounts and returns, depreciable and amortizable lives, recoverability of inventories, including those produced in preparation for product launches, amounts recorded for contingencies, environmental liabilities, accruals for contingent sales-based milestone payments and other reserves, pension and other postretirement benefit plan assumptions, share-based compensation assumptions, restructuring costs, impairments of long-lived assets (including intangible assets and goodwill) and investments, and taxes on income. Because of the uncertainty inherent in such estimates, actual results may differ from these estimates. Reclassifications — Certain reclassifications have been made to prior year amounts to conform to the current year presentation. Recently Adopted Accounting Standards — In May 2014, the Financial Accounting Standards Board (FASB) issued amended accounting guidance on revenue recognition (ASU 2014-09) that applies to all contracts with customers. The objective of the new guidance is to improve comparability of revenue recognition practices across entities and to provide more useful information to users of financial statements through improved disclosure requirements. The new standard permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of adopting the guidance being recognized at the date of initial application (modified retrospective method). The new standard was effective as of January 1, 2018 and was adopted using the modified retrospective method. The Company recorded a cumulative-effect adjustment upon adoption increasing Retained earnings by $5 million . In January 2016, the FASB issued revised guidance for the accounting and reporting of financial instruments (ASU 2016-01) and in 2018 issued related technical corrections (ASU 2018-03). The new guidance requires that equity investments with readily determinable fair values currently classified as available for sale be measured at fair value with changes in fair value recognized in net income. The Company has elected to measure equity investments without readily determinable fair values at cost, adjusted for subsequent observable price changes and less impairments, which will be recognized in net income. The new guidance also changed certain disclosure requirements. ASU 2016-01 was effective as of January 1, 2018 and was adopted using a modified retrospective approach. The Company recorded a cumulative-effect adjustment upon adoption increasing Retained earnings by $8 million . ASU 2018-03 was also adopted as of January 1, 2018 on a prospective basis and did not result in any additional impacts upon adoption. In October 2016, the FASB issued guidance on the accounting for the income tax consequences of intra-entity transfers of assets other than inventory (ASU 2016-16). The new guidance requires the recognition of the income tax consequences of an intra-entity transfer of an asset (with the exception of inventory) when the intra-entity transfer occurs, replacing the prohibition against doing so. The current exception to defer the recognition of any tax impact on the transfer of inventory within the consolidated entity until it is sold to a third party remains unaffected. The new standard was effective as of January 1, 2018 and was adopted using a modified retrospective approach. The Company recorded a cumulative-effect adjustment upon adoption increasing Retained earnings by $54 million with a corresponding decrease to Deferred Income Taxes . In August 2017, the FASB issued new guidance on hedge accounting (ASU 2017-12) that is intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. The new guidance makes more financial and nonfinancial hedging strategies eligible for hedge accounting, amends the presentation and disclosure requirements, and changes how companies assess effectiveness. The Company elected to early adopt this guidance as of January 1, 2018 on a modified retrospective basis. The new guidance was applied to all existing hedges as of the adoption date. For fair value hedges of interest rate risk outstanding as of the date of adoption, the Company recorded a cumulative-effect adjustment upon adoption to the basis adjustment on the hedged item resulting from applying the benchmark component of the coupon guidance. This adjustment decreased Retained earnings by $11 million . Also, in accordance with the transition provisions of AS

Acquisitions, Divestitures, Res

Acquisitions, Divestitures, Research Collaborations and License Agreements	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Acquisitions, Divestitures, Research Collaborations and License Agreements	Acquisitions, Divestitures, Research Collaborations and License Agreements The Company continues to pursue the acquisition of businesses and establishment of external alliances such as research collaborations and licensing agreements to complement its internal research capabilities. These arrangements often include upfront payments, as well as expense reimbursements or payments to the third party, and milestone, royalty or profit share arrangements, contingent upon the occurrence of certain future events linked to the success of the asset in development. The Company also reviews its marketed products and pipeline to examine candidates which may provide more value through out-licensing and, as part of its portfolio assessment process, may also divest certain assets. Pro forma financial information for acquired businesses is not presented if the historical financial results of the acquired entity are not significant when compared with the Company’s financial results. Recently Announced Transaction In December 2018, Merck and privately held Antelliq Group (Antelliq) signed a definitive agreement under which Merck will acquire Antelliq from funds advised by BC Partners. Antelliq is a leader in digital animal identification, traceability and monitoring solutions. These solutions help veterinarians, farmers and pet owners gather critical data to improve management, health and well-being of livestock and pets. Merck will make a cash payment of approximately €2.1 billion (approximately $2.4 billion based on exchange rates at the time of the announcement) to acquire all outstanding shares of Antelliq and will assume Antelliq’s debt of €1.1 billion (approximately $1.3 billion ), which it intends to repay shortly after the closing of the acquisition. The transaction is subject to clearance by antitrust and competition law authorities and other customary closing conditions, and is expected to close in the second quarter of 2019. 2018 Transactions In 2018, the Company recorded an aggregate charge of $423 million within Cost of sales in conjunction with the termination of a collaboration agreement entered into in 2014 with Samsung Bioepis Co., Ltd. (Samsung) for insulin glargine. The charge reflects a termination payment of $155 million , which represents the reimbursement of all fees previously paid by Samsung to Merck under the agreement, plus interest, as well as the release of Merck’s ongoing obligations under the agreement. The charge also included fixed asset abandonment charges of $137 million , inventory write-offs of $122 million , as well as other related costs of $9 million . The termination of this agreement has no impact on the Company’s other collaboration with Samsung. In June 2018, Merck acquired Viralytics Limited (Viralytics), an Australian publicly traded company focused on oncolytic immunotherapy treatments for a range of cancers, for AUD 502 million ( $378 million ). The transaction provided Merck with full rights to Cavatak (V937, formerly CVA21), Viralytics’s investigational oncolytic immunotherapy. Cavatak is based on Viralytics’s proprietary formulation of an oncolytic virus (Coxsackievirus Type A21) that has been shown to preferentially infect and kill cancer cells. Cavatak is currently being evaluated in multiple Phase 1 and Phase 2 clinical trials, both as an intratumoral and intravenous agent, including in combination with Keytruda . Under a previous agreement between Merck and Viralytics, a study is investigating the use of the Keytruda and Cavatak combination in melanoma, prostate, lung and bladder cancers. The transaction was accounted for as an acquisition of an asset. Merck recorded net assets of $34 million (primarily cash) at the acquisition date and Research and development expenses of $344 million in 2018 related to the transaction. There are no future contingent payments associated with the acquisition. In March 2018, Merck and Eisai Co., Ltd. (Eisai) entered into a strategic collaboration for the worldwide co-development and co-commercialization of Lenvima, an orally available tyrosine kinase inhibitor discovered by Eisai (see Note 4). 2017 Transactions In October 2017, Merck acquired Rigontec GmbH (Rigontec). Rigontec is a leader in accessing the retinoic acid-inducible gene I pathway, part of the innate immune system, as a novel and distinct approach in cancer immunotherapy to induce both immediate and long-term anti-tumor immunity. Rigontec’s lead candidate, MK-4621 (formerly RGT100), is currently in Phase I development evaluating treatment in patients with various tumors. Under the terms of the agreement, Merck made an upfront cash payment of €119 million ( $140 million ) and may make additional contingent payments of up to €349 million (of which €184 million are related to the achievement of research milestones and regulatory approvals and €165 million are related to the achievement of commercial targets). The transaction was accounted for as an acquisition of an asset and the upfront payment is reflected within Research and development expenses in 2017. In July 2017, Merck and AstraZeneca PLC (AstraZeneca) entered into a global strategic oncology collaboration to co-develop and co-commercialize AstraZeneca’s Lynparza for multiple cancer types (see Note 4). In March 2017, Merck acquired a controlling interest in Vallée S.A. (Vallée), a leading privately held producer of animal health products in Brazil. Vallée has an extensive portfolio of products spanning parasiticides, anti-infectives and vaccines that include products for livestock, horses, and companion animals. Under the terms of the agreement, Merck acquired 93.5% of the shares of Vallée for $358 million . Of the total purchase price, $176 million was placed into escrow pending resolution of certain contingent items. The transaction was accounted for as an acquisition of a business. Merck recognized intangible assets of $297 million related to currently marketed products, net deferred tax liabilities of $102 million , other net assets of $32 million and noncontrolling interest of $25 million . In addition, the Company recorded liabilities of $37 million for contingencies identified at the acquisition date and corresponding indemnification assets of $37 million , representing the amounts to be reimbursed to Merck if and when the contingent liabilities are paid. The excess of the consideration transferred over the fair value of net assets acquired of $156 million was recorded as goodwill. The goodwill was allocated to the Animal Health segment and is not deductible for tax purposes. The estimated fair values of identifiable intangible assets related to currently marketed products were determined using an income approach. The probability-adjusted future net cash flows of each product were discounted to present value utilizing a discount rate of 15.5% . Actual cash flows are likely to be different than those assumed. The intangible assets related to currently marketed products are being amortized over their estimated useful lives of 15 years. In the fourth quarter of 2017, Merck acquired an additional 4.5% interest in Vallée for $18 million , which reduced the noncontrolling interest related to Vallée. 2016 Transactions In July 2016, Merck acquired Afferent Pharmaceuticals (Afferent), a privately held pharmaceutical company focused on the development of therapeutic candidates targeting the P2X3 receptor for the treatment of common, poorly-managed, neurogenic conditions. Afferent’s lead investigational candidate, MK-7264 (formerly AF-219), gefapixant, is a selective, non-narcotic, orally-administered P2X3 antagonist being evaluated for the treatment of refractory, chronic cough and for the treatment of endometriosis-related pain. Total consideration transferred of $510 million included cash paid for outstanding Afferent shares of $487 million , as well as share-based compensation payments to settle equity awards attributable to precombination service and cash paid for transaction costs on behalf of Afferent. In addition, former Afferent shareholders are eligible to receive a total of up to an additional $750 million contingent upon the attainment of certain clinical development and commercial milestones for multiple indications and candidates, including MK-7264. This transaction was accounted for as an acquisition of a business. The Company determined the fair value of the contingent consideration was $223 million at the acquisition date utilizing a probability-weighted estimated cash flow stream using an appropriate discount rate dependent on the nature and timing of the milestone payment. Merck recognized an intangible asset for IPR&D of $832 million , net deferred tax liabilities of $258 million , and other net assets of $29 million (primarily consisting of cash acquired). The excess of the consideration transferred over the fair value of net assets acquired of $130 million was recorded as goodwill that was allocated to the Pharmaceutical segment and is not deductible for tax purposes. The fair value of the identifiable intangible asset related to IPR&D was determined using an income approach. The asset’s probability-adjusted future net cash flows were discounted to present value using a discount rate of 11.5% . Actual cash flows are likely to be different than those assumed. In 2018, as a result of the achievement of a clinical development milestone, Merck made a $175 million payment, which was accrued for at estimated fair value at the time of acquisition as noted above. The contingent consideration liability was then remeasured at current fair value at each subsequent reporting period until payment was made (see Note 6). In June 2016, Merck and Moderna Therapeutics (Moderna) entered into a strategic collaboration and license agreement to develop and commercialize novel messenger RNA (mRNA)-based personalized cancer vaccines. The development program will entail multiple studies in several types of cancer and include the evaluation of mRNA-based personalized cancer vaccines in combination with Merck’s Keytruda . Pursuant to the terms of the agreement, Merck made an upfront cash payment to Moderna of $200 million , which was recorded in Research and development expenses. Following human proof of concept studies, Merck has the right to elect to make an additional payment to Moderna. If Merck exercises this right, the two companies will then equally share costs and profits under a worldwide collaboration for the development of personalized cancer vaccines. Moderna will have the right to elect to co-promote the personalized cancer vaccines in the United States. The agreement entails exclusivity around combinations with Keytruda . Moderna and Merck each have the ability to combine mRNA-based personalized cancer vaccines with other (non-PD-1) agents. In January 2016, Merck acquired IOmet Pharma Ltd (IOmet), a privately held UK-based drug discovery company focused on the development of innovative medicines for the treatment of cancer, with a particular emphasis on the fields of cancer immunotherapy and cancer metabolism. The acquisition provided Merck with IOmet’s preclinical pipeline of IDO (indoleamine-2,3-dioxygenase 1), TDO (tryptophan-2,3-dioxygenase), and dual-acting IDO/TDO inhibitors. The transaction was accounted for as an acquisition of a business. Total purchase consideration in the transaction included a cash payment of $150 million and future additional milestone payments of up to $250 million contingent upon certain clinical and regulatory milestones being achieved. The Company determined the fair value of the contingent consideration was $94 million at the acquisition date utilizing a probability-weighted estimated cash flow stream adjusted for the expected timing of each payment utilizing a discount rate of 10.5% . Merck recognized intangible assets for IPR&D of $155 million and net deferred tax assets of $32 million . The excess of the consideration transferred over the fair value of net assets acquired of $57 million was recorded as goodwill that was allocated to the Pharmaceutical segment and is not deductible for tax purposes. The fair values of the identifiable intangible assets related to IPR&D were determined using an income approach. The assets’ probability-adjusted future net cash flows were discounted to present value also using a discount rate of 10.5% . Actual cash flows are likely to be different than those assumed. In 2017, as a result of the achievement of a clinical development milestone, Merck made a $100 million payment, which was accrued for at estimated fair value at the time of acquisition as noted above. The contingent consideration liability was then remeasured at current fair value at each subsequent reporting period until payment was made (see Note 6). Remicade/Simponi In 1998, a subsidiary of Schering-Plough entered into a licensing agreement with Centocor Ortho Biotech Inc. (Centocor), a Johnson & Johnson (J&J) company, to market Remicade, which is prescribed for the treatment of inflammatory diseases. In 2005, Schering-Plough’s subsidiary exercised an option under its contract with Centocor for license rights to develop and commercialize Simponi , a fully human monoclonal antibody. The Company has marketing rights to both products throughout Europe, Russia and Turkey. Remicade lost market exclusivity in major European markets in 2015 and the Company no longer has market exclusivity in any of its marketing territories . The Company continues to have market exclusivity for Simponi in all of its marketing territories. All profits derived from Merck’s distribution of the two products in these countries are equally divided between Merck and J&J.

Collaborative Arrangements

Collaborative Arrangements	12 Months Ended
	Dec. 31, 2018
Collaborative Arrangements [Abstract]
Collaborative Arrangements	Collaborative Arrangements Merck has entered into collaborative arrangements that provide the Company with varying rights to develop, produce and market products together with its collaborative partners. Both parties in these arrangements are active participants and exposed to significant risks and rewards dependent on the commercial success of the activities of the collaboration. Merck’s more significant collaborative arrangements are discussed below. AstraZeneca In July 2017, Merck and AstraZeneca entered into a global strategic oncology collaboration to co-develop and co-commercialize AstraZeneca’s Lynparza for multiple cancer types. Lynparza is an oral poly (ADP-ribose) polymerase (PARP) inhibitor currently approved for certain types of ovarian and breast cancer. The companies are jointly developing and commercializing Lynparza, both as monotherapy and in combination trials with other potential medicines. Independently, Merck and AstraZeneca will develop and commercialize Lynparza in combinations with their respective PD-1 and PD-L1 medicines, Keytruda and Imfinzi. The companies will also jointly develop and commercialize AstraZeneca’s selumetinib, an oral, potent, selective inhibitor of MEK, part of the mitogen-activated protein kinase (MAPK) pathway, currently being developed for multiple indications. Under the terms of the agreement, AstraZeneca and Merck will share the development and commercialization costs for Lynparza and selumetinib monotherapy and non-PD-L1/PD-1 combination therapy opportunities. Gross profits from Lynparza and selumetinib product sales generated through monotherapies or combination therapies are shared equally. Merck will fund all development and commercialization costs of Keytruda in combination with Lynparza or selumetinib. AstraZeneca will fund all development and commercialization costs of Imfinzi in combination with Lynparza or selumetinib. AstraZeneca is currently the principal on Lynparza sales transactions. Merck records its share of Lynparza product sales, net of cost of sales and commercialization costs, as alliance revenue within the Pharmaceutical segment and its share of development costs associated with the collaboration as part of Research and development expenses. Reimbursements received from AstraZeneca for research and development expenses are recognized as reductions to Research and development costs. As part of the agreement, Merck made an upfront payment to AstraZeneca of $1.6 billion and will make payments of up to $750 million over a multi-year period for certain license options (of which $250 million was paid in December 2017, $400 million was paid in December 2018 and $100 million is expected be paid in 2019). The Company recorded an aggregate charge of $2.35 billion in Research and development expenses in 2017 related to the upfront payment and future license option payments. In addition, the agreement provides for additional contingent payments from Merck to AstraZeneca related to the successful achievement of regulatory and sales-based milestones. In 2018, Merck determined it was probable that annual sales of Lynparza in the future would trigger three sales-based milestone payments from Merck to AstraZeneca aggregating $600 million . Accordingly, in 2018, Merck recorded $600 million of liabilities and a corresponding increase to the intangible asset related to Lynparza, and recognized $58 million of cumulative amortization expense within Cost of sales . During 2018, one of the sales-based milestones was triggered, resulting in a $150 million payment to AstraZeneca. In 2018, Merck made an additional $100 million sales-based milestone payment, which was accrued for in 2017 when the Company deemed to the payment to be probable. The remaining $3.4 billion of potential future sales-based milestone payments have not yet been accrued as they are not deemed by the Company to be probable at this time. In 2018, Lynparza received approval in the United States for the treatment of certain patients with metastatic breast cancer and for use in the first-line maintenance setting for advanced ovarian cancer, triggering capitalized milestone payments of $140 million in the aggregate from Merck to AstraZeneca. Potential future regulatory milestone payments of $1.76 billion remain under the agreement. The asset balance related to Lynparza (which includes capitalized sales-based and regulatory milestone payments) was $743 million at December 31, 2018 and is included in Other Assets on the Consolidated Balance Sheet. The amount is being amortized over its estimated useful life through 2028 as supported by projected future cash flows, subject to impairment testing. Summarized information related to this collaboration is as follows: Years Ended December 31 2018 2017 Alliance revenue $ 187 $ 20 Cost of sales (1) 93 4 Selling, general and administrative 48 1 Research and development (2) 152 2,419 December 31 2018 2017 Receivables from AstraZeneca included in Other current assets $ 52 $ 12 Payables to AstraZeneca included in Accrued and other current liabilities (3) 405 543 Payables to AstraZeneca included Other Noncurrent Liabilities (3) 250 100 (1) Represents amortization of capitalized milestone payments. (2) Amount for 2017 includes $2.35 billion related to the upfront payment and future license option payments. (3) Includes accrued milestone and license option payments. Eisai In March 2018, Merck and Eisai announced a strategic collaboration for the worldwide co-development and co-commercialization of Lenvima, an orally available tyrosine kinase inhibitor discovered by Eisai. Under the agreement, Merck and Eisai will develop and commercialize Lenvima jointly, both as monotherapy and in combination with Merck’s anti-PD-1 therapy, Keytruda . Eisai records Lenvima product sales globally (Eisai is the principal on Lenvima sales transactions), and Merck and Eisai share gross profits equally. Merck records its share of Lenvima product sales, net of cost of sales and commercialization costs, as alliance revenue. Expenses incurred during co-development, including for studies evaluating Lenvima as monotherapy, are shared equally by the two companies and reflected in Research and development expenses. Under the agreement, Merck made an upfront payment to Eisai of $750 million and will make payments of up to $650 million for certain option rights through 2021 (of which $325 million will be paid in March 2019, $200 million is expected to be paid in 2020 and $125 million is expected to be paid in 2021). The Company recorded an aggregate charge of $1.4 billion in Research and development expenses in 2018 related to the upfront payment and future option payments. In addition, the agreement provides for Eisai to receive up to $385 million associated with the achievement of certain clinical and regulatory milestones and up to $3.97 billion for the achievement of milestones associated with sales of Lenvima. In 2018, Merck determined it was probable that annual sales of Lenvima in the future would trigger three sales-based milestone payments from Merck to Eisai aggregating $268 million . Accordingly, in 2018, Merck recorded $268 million of liabilities and a corresponding increase to the intangible asset related to Lenvima, and recognized $24 million of cumulative amortization expense within Cost of sales . The remaining $3.71 billion of potential future sales-based milestone payments have not yet been accrued as they are not deemed by the Company to be probable at this time. In 2018, Lenvima was approved for the treatment of patients with unresectable hepatocellular carcinoma in the United States, the European Union, Japan and China, triggering capitalized milestone payments to Eisai of $250 million in the aggregate. Potential future regulatory milestone payments of $135 million remain under the agreement. The asset balance related to Lenvima (which includes capitalized sales-based and regulatory milestone payments) was $479 million at December 31, 2018 and is included in Other Assets on the Consolidated Balance Sheet. The amount is being amortized over its estimated useful life through 2026 as supported by projected future cash flows, subject to impairment testing. Summarized information related to this collaboration is as follows: Year Ended December 31 2018 Alliance revenue $ 149 Cost of sales (1) 39 Selling, general and administrative 13 Research and development (2) 1,489 December 31 2018 Receivables from Eisai included in Other current assets $ 71 Payables to Eisai included in Accrued and other current liabilities (3) 375 Payables to Eisai included in Other Noncurrent Liabilities (3) 543 (1) Represents amortization of capitalized milestone payments. (2) Includes $1.4 billion related to the upfront payment and future option payments. (3) Includes accrued milestone and option payments. Bayer AG In 2014, the Company entered into a worldwide clinical development collaboration with Bayer AG (Bayer) to market and develop soluble guanylate cyclase (sGC) modulators including Bayer’s Adempas, which is approved to treat pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. The two companies have implemented a joint development and commercialization strategy. The collaboration also includes clinical development of Bayer’s vericiguat, which is in Phase 3 trials for worsening heart failure, as well as opt-in rights for other early-stage sGC compounds in development by Bayer. Merck in turn made available its early-stage sGC compounds under similar terms. Under the agreement, Bayer leads commercialization of Adempas in the Americas, while Merck leads commercialization in the rest of the world. For vericiguat and other potential opt-in products, Bayer will lead commercialization in the rest of world and Merck will lead in the Americas. For all products and candidates included in the agreement, both companies will share in development costs and profits on sales and will have the right to co-promote in territories where they are not the lead. In 2016, Merck began promoting and distributing Adempas in Europe. Transition from Bayer in other Merck territories, including Japan, continued in 2017. Revenue from Adempas includes sales in Merck’s marketing territories, as well as Merck’s share of profits from the sale of Adempas in Bayer’s marketing territories. In 2018, Merck determined it was probable that annual worldwide sales of Adempas in the future would trigger a $375 million sales-based milestone payment from Merck to Bayer. Accordingly, Merck recorded a $375 million noncurrent liability and a corresponding increase to the intangible asset related to Adempas, and recognized $106 million of cumulative amortization expense within Cost of sales . In 2018, the Company made a $350 million milestone payment to Bayer, which was accrued for in 2016 when Merck deemed the payment to be probable. There is an additional $400 million potential future sales-based milestone payment that has not yet been accrued as it is not deemed by the Company to be probable at this time. The intangible asset balance related to Adempas (which includes the remaining acquired intangible asset balance, as well as capitalized sales-based milestone payments) was $1.0 billion at December 31, 2018 and is included in Other Intangibles, Net on the Consolidated Balance Sheet. The amount is being amortized over its estimated useful life through 2027 as supported by projected future cash flows, subject to impairment testing. Summarized information related to this collaboration is as follows: Years Ended December 31 2018 2017 2016 Net product sales recorded by Merck $ 190 $ 149 $ 88 Merck’s profit share from sales in Bayer’s marketing territories 139 151 81 Total sales 329 300 169 Cost of sales (1) 216 99 133 Selling, general and administrative 35 27 26 Research and development 127 101 82 December 31 2018 2017 Receivables from Bayer included in Other current assets $ 32 $ 33 Payables to Bayer included in Accrued and other current liabilities (2) — 350 Payables to Bayer included in Other Noncurrent Liabilities (2) 375 — (1) Includes amortization of intangible assets. (2) Includes accrued milestone payments. Aggregate amortization expense related to capitalized license costs recorded within Cost of sales was $186 million in 2018 , $39 million in 2017 and $30 million in 2016 . The estimated aggregate amortization expense for each of the next five years is as follows: 2019 , $196 million ; 2020 , $193 million ; 2021 , $191 million ; 2022 , $187 million ; 2023 , $181 million .

Restructuring

Restructuring	12 Months Ended
	Dec. 31, 2018
Restructuring and Related Activities [Abstract]
Restructuring	Restructuring In 2010 and 2013, the Company commenced actions under global restructuring programs designed to streamline its cost structure. The actions under these programs include the elimination of positions in sales, administrative and headquarters organizations, as well as the sale or closure of certain manufacturing and research and development sites and the consolidation of office facilities. The Company also continues to reduce its global real estate footprint and improve the efficiency of its manufacturing and supply network. The Company recorded total pretax costs of $658 million in 2018 , $927 million in 2017 and $1.1 billion in 2016 related to restructuring program activities. Since inception of the programs through December 31, 2018 , Merck has recorded total pretax accumulated costs of approximately $14.1 billion and eliminated approximately 45,510 positions comprised of employee separations, as well as the elimination of contractors and vacant positions. The Company estimates that approximately two-thirds of the cumulative pretax costs are cash outlays, primarily related to employee separation expense. Approximately one-third of the cumulative pretax costs are non-cash, relating primarily to the accelerated depreciation of facilities to be closed or divested. The Company has substantially completed the actions under these programs. For segment reporting, restructuring charges are unallocated expenses. The following table summarizes the charges related to restructuring program activities by type of cost: Separation Costs Accelerated Depreciation Other Total Year Ended December 31, 2018 Cost of sales $ — $ 10 $ 11 $ 21 Selling, general and administrative — 2 1 3 Research and development — (13 ) 15 2 Restructuring costs 473 — 159 632 $ 473 $ (1 ) $ 186 $ 658 Year Ended December 31, 2017 Cost of sales $ — $ 52 $ 86 $ 138 Selling, general and administrative — 2 — 2 Research and development — 6 5 11 Restructuring costs 552 — 224 776 $ 552 $ 60 $ 315 $ 927 Year Ended December 31, 2016 Cost of sales $ — $ 77 $ 104 $ 181 Selling, general and administrative — 8 87 95 Research and development — 142 — 142 Restructuring costs 216 — 435 651 $ 216 $ 227 $ 626 $ 1,069 Separation costs are associated with actual headcount reductions, as well as those headcount reductions which were probable and could be reasonably estimated. Positions eliminated under restructuring program activities were approximately 2,160 in 2018 , 2,450 in 2017 and 2,625 in 2016 . Accelerated depreciation costs primarily relate to manufacturing, research and administrative facilities and equipment to be sold or closed as part of the programs. Accelerated depreciation costs represent the difference between the depreciation expense to be recognized over the revised useful life of the asset, based upon the anticipated date the site will be closed or divested or the equipment disposed of, and depreciation expense as determined utilizing the useful life prior to the restructuring actions. All the sites have and will continue to operate up through the respective closure dates and, since future undiscounted cash flows were sufficient to recover the respective book values, Merck is recording accelerated depreciation over the revised useful life of the site assets. Anticipated site closure dates, particularly related to manufacturing locations, have been and may continue to be adjusted to reflect changes resulting from regulatory or other factors. Other activity in 2018 , 2017 and 2016 includes $141 million , $267 million and $409 million , respectively, of asset abandonment, shut-down and other related costs. Additionally, other activity includes certain employee-related costs associated with pension and other postretirement benefit plans (see Note 14) and share-based compensation. Other activity also reflects net pretax losses resulting from sales of facilities and related assets of $151 million in 2016 . The following table summarizes the charges and spending relating to restructuring program activities: Separation Costs Accelerated Depreciation Other Total Restructuring reserves January 1, 2017 $ 395 $ — $ 146 $ 541 Expenses 552 60 315 927 (Payments) receipts, net (328 ) — (394 ) (722 ) Non-cash activity — (60 ) 61 1 Restructuring reserves December 31, 2017 619 — 128 747 Expenses 473 (1 ) 186 658 (Payments) receipts, net (649 ) — (238 ) (887 ) Non-cash activity — 1 15 16 Restructuring reserves December 31, 2018 (1) $ 443 $ — $ 91 $ 534 (1) The remaining cash outlays are expected to be substantially completed by the end of 2020.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Financial Instruments	Financial Instruments Derivative Instruments and Hedging Activities The Company manages the impact of foreign exchange rate movements and interest rate movements on its earnings, cash flows and fair values of assets and liabilities through operational means and through the use of various financial instruments, including derivative instruments. A significant portion of the Company’s revenues and earnings in foreign affiliates is exposed to changes in foreign exchange rates. The objectives and accounting related to the Company’s foreign currency risk management program, as well as its interest rate risk management activities are discussed below. Foreign Currency Risk Management The Company has established revenue hedging, balance sheet risk management and net investment hedging programs to protect against volatility of future foreign currency cash flows and changes in fair value caused by volatility in foreign exchange rates. The objective of the revenue hedging program is to reduce the variability caused by changes in foreign exchange rates that would affect the U.S. dollar value of future cash flows derived from foreign currency denominated sales, primarily the euro and Japanese yen. To achieve this objective, the Company will hedge a portion of its forecasted foreign currency denominated third-party and intercompany distributor entity sales (forecasted sales) that are expected to occur over its planning cycle, typically no more than two years into the future. The Company will layer in hedges over time, increasing the portion of forecasted sales hedged as it gets closer to the expected date of the forecasted sales. The portion of forecasted sales hedged is based on assessments of cost-benefit profiles that consider natural offsetting exposures, revenue and exchange rate volatilities and correlations, and the cost of hedging instruments. The Company manages its anticipated transaction exposure principally with purchased local currency put options, forward contracts, and purchased collar options. The fair values of these derivative contracts are recorded as either assets (gain positions) or liabilities (loss positions) in the Consolidated Balance Sheet. Changes in the fair value of derivative contracts are recorded each period in either current earnings or OCI , depending on whether the derivative is designated as part of a hedge transaction and, if so, the type of hedge transaction. For derivatives that are designated as cash flow hedges, the unrealized gains or losses on these contracts is recorded in AOCI and reclassified into Sales when the hedged anticipated revenue is recognized. For those derivatives which are not designated as cash flow hedges, but serve as economic hedges of forecasted sales, unrealized gains or losses are recorded in Sales each period. The cash flows from both designated and non-designated contracts are reported as operating activities in the Consolidated Statement of Cash Flows. The Company does not enter into derivatives for trading or speculative purposes. The Company manages operating activities and net asset positions at each local subsidiary in order to mitigate the effects of exchange on monetary assets and liabilities. The Company also uses a balance sheet risk management program to mitigate the exposure of net monetary assets that are denominated in a currency other than a subsidiary’s functional currency from the effects of volatility in foreign exchange. In these instances, Merck principally utilizes forward exchange contracts to offset the effects of exchange on exposures denominated in developed country currencies, primarily the euro and Japanese yen. For exposures in developing country currencies, the Company will enter into forward contracts to partially offset the effects of exchange on exposures when it is deemed economical to do so based on a cost-benefit analysis that considers the magnitude of the exposure, the volatility of the exchange rate and the cost of the hedging instrument. The cash flows from these contracts are reported as operating activities in the Consolidated Statement of Cash Flows. Monetary assets and liabilities denominated in a currency other than the functional currency of a given subsidiary are remeasured at spot rates in effect on the balance sheet date with the effects of changes in spot rates reported in Other (income) expense, net . The forward contracts are not designated as hedges and are marked to market through Other (income) expense, net . Accordingly, fair value changes in the forward contracts help mitigate the changes in the value of the remeasured assets and liabilities attributable to changes in foreign currency exchange rates, except to the extent of the spot-forward differences. These differences are not significant due to the short-term nature of the contracts, which typically have average maturities at inception of less than one year . The Company also uses forward exchange contracts to hedge its net investment in foreign operations against movements in exchange rates. The forward contracts are designated as hedges of the net investment in a foreign operation. The Company hedges a portion of the net investment in certain of its foreign operations. The unrealized gains or losses on these contracts are recorded in foreign currency translation adjustment within OCI , and remain in AOCI until either the sale or complete or substantially complete liquidation of the subsidiary. The Company excludes certain portions of the change in fair value of its derivative instruments from the assessment of hedge effectiveness (excluded component). Changes in fair value of the excluded components are recognized in OCI . In accordance with the new guidance adopted on January 1, 2018 (see Note 2), the Company has elected to recognize in earnings the initial value of the excluded component on a straight-line basis over the life of the derivative instrument, rather than using the mark-to-market approach. The cash flows from these contracts are reported as investing activities in the Consolidated Statement of Cash Flows. Foreign exchange risk is also managed through the use of foreign currency debt. The Company’s senior unsecured euro-denominated notes have been designated as, and are effective as, economic hedges of the net investment in a foreign operation. Accordingly, foreign currency transaction gains or losses due to spot rate fluctuations on the euro-denominated debt instruments are included in foreign currency translation adjustment within OCI . The effects of the Company’s net investment hedges on OCI and the Consolidated Statement of Income are shown below: Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income (1) Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing Years Ended December 31 2018 2017 2016 2018 2017 2016 Net Investment Hedging Relationships Foreign exchange contracts $ (18 ) $ — $ 2 $ (11 ) $ — $ (1 ) Euro-denominated notes (183 ) 520 (193 ) — — — (1) No amounts were reclassified from AOCI into income related to the sale of a subsidiary. Interest Rate Risk Management The Company may use interest rate swap contracts on certain investing and borrowing transactions to manage its net exposure to interest rate changes and to reduce its overall cost of borrowing. The Company does not use leveraged swaps and, in general, does not leverage any of its investment activities that would put principal capital at risk. In May 2018, four interest rate swaps with notional amounts aggregating $1.0 billion matured. These swaps effectively converted the Company’s $1.0 billion , 1.30% fixed-rate notes due 2018 to variable rate debt. In December 2018, in connection with the early repayment of debt, the Company settled three interest rate swaps with notional amounts aggregating $550 million . These swaps effectively converted a portion of the Company’s $1.25 billion , 5.00% notes due 2019 to variable rate debt. At December 31, 2018 , the Company was a party to 19 pay-floating, receive-fixed interest rate swap contracts designated as fair value hedges of fixed-rate notes in which the notional amounts match the amount of the hedged fixed-rate notes as detailed in the table below. 2018 Debt Instrument Par Value of Debt Number of Interest Rate Swaps Held Total Swap Notional Amount 1.85% notes due 2020 $ 1,250 5 $ 1,250 3.875% notes due 2021 1,150 5 1,150 2.40% notes due 2022 1,000 4 1,000 2.35% notes due 2022 1,250 5 1,250 The interest rate swap contracts are designated hedges of the fair value changes in the notes attributable to changes in the benchmark London Interbank Offered Rate (LIBOR) swap rate. The fair value changes in the notes attributable to changes in the LIBOR swap rate are recorded in interest expense along with the offsetting fair value changes in the swap contracts. The cash flows from these contracts are reported as operating activities in the Consolidated Statement of Cash Flows. The table below presents the location of amounts recorded on the Consolidated Balance Sheet related to cumulative basis adjustments for fair value hedges as of December 31: Carrying Amount of Hedged Liabilities Cumulative Amount of Fair Value Hedging Adjustment Increase (Decrease) Included in the Carrying Amount 2018 2017 2018 2017 Balance Sheet Line Item in which Hedged Item is Included Loans payable and current portion of long-term debt $ — $ 983 $ — $ (17 ) Long-Term Debt (1) 4,560 5,146 (82 ) (41 ) (1) Amounts include hedging adjustment gains related to discontinued hedging relationships of $11 million at December 31, 2017. Presented in the table below is the fair value of derivatives on a gross basis segregated between those derivatives that are designated as hedging instruments and those that are not designated as hedging instruments as of December 31: 2018 2017 Fair Value of Derivative U.S. Dollar Notional Fair Value of Derivative U.S. Dollar Notional Balance Sheet Caption Asset Liability Asset Liability Derivatives Designated as Hedging Instruments Interest rate swap contracts Other assets $ — $ — $ — $ 2 $ — $ 550 Interest rate swap contracts Accrued and other current liabilities — — — — 3 1,000 Interest rate swap contracts Other noncurrent liabilities — 81 4,650 — 52 4,650 Foreign exchange contracts Other current assets 263 — 6,222 51 — 4,216 Foreign exchange contracts Other assets 75 — 2,655 38 — 1,936 Foreign exchange contracts Accrued and other current liabilities — 7 774 — 71 2,014 Foreign exchange contracts Other noncurrent liabilities — 1 89 — 1 20 $ 338 $ 89 $ 14,390 $ 91 $ 127 $ 14,386 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts Other current assets $ 116 $ — $ 5,430 $ 39 $ — $ 3,778 Foreign exchange contracts Accrued and other current liabilities — 71 9,922 — 90 7,431 $ 116 $ 71 $ 15,352 $ 39 $ 90 $ 11,209 $ 454 $ 160 $ 29,742 $ 130 $ 217 $ 25,595 As noted above, the Company records its derivatives on a gross basis in the Consolidated Balance Sheet. The Company has master netting agreements with several of its financial institution counterparties (see Concentrations of Credit Risk below). The following table provides information on the Company’s derivative positions subject to these master netting arrangements as if they were presented on a net basis, allowing for the right of offset by counterparty and cash collateral exchanged per the master agreements and related credit support annexes at December 31: 2018 2017 Asset Liability Asset Liability Gross amounts recognized in the consolidated balance sheet $ 454 $ 160 $ 130 $ 217 Gross amount subject to offset in master netting arrangements not offset in the consolidated balance sheet (121 ) (121 ) (94 ) (94 ) Cash collateral received (107 ) — (3 ) — Net amounts $ 226 $ 39 $ 33 $ 123 The table below provides information regarding the location and amount of pretax (gains) losses of derivatives designated in fair value or cash flow hedging relationships: Sales Other (income) expense, net (1) Other comprehensive income (loss) Years Ended December 31 2018 2017 2016 2018 2017 2016 2018 2017 2016 Financial Statement Line Items in which Effects of Fair Value or Cash Flow Hedges are Recorded $ 42,294 $ 40,122 $ 39,807 $ (402 ) (500 ) 189 $ (361 ) $ 316 $ (1,078 ) (Gain) loss on fair value hedging relationships Interest rate swap contracts Hedged items — — — (27 ) (48 ) (29 ) — — — Derivatives designated as hedging instruments — — — 50 12 (35 ) — — — Impact of cash flow hedging relationships Foreign exchange contracts Amount of gain (loss) recognized in OCI on derivatives — — — — — — 228 (562 ) 210 (Decrease) increase in Sales as a result of AOCI reclassifications (160 ) 138 311 — — — 160 (138 ) (311 ) (1) Interest expense is a component of Other (income) expense, net. The table below provides information regarding the income statement effects of derivatives not designated as hedging instruments: Amount of Derivative Pretax (Gain) Loss Recognized in Income Years Ended December 31 Income Statement Caption 2018 2017 2016 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts (1) Other (income) expense, net $ (260 ) $ 110 $ 132 Foreign exchange contracts (2) Sales (8 ) (3 ) — (1) These derivative contracts mitigate changes in the value of remeasured foreign currency denominated monetary assets and liabilities attributable to changes in foreign currency exchange rates. (2) These derivative contracts serve as economic hedges of forecasted transactions. At December 31, 2018 , the Company estimates $186 million of pretax net unrealized gains on derivatives maturing within the next 12 months that hedge foreign currency denominated sales over that same period will be reclassified from AOCI to Sales . The amount ultimately reclassified to Sales may differ as foreign exchange rates change. Realized gains and losses are ultimately determined by actual exchange rates at maturity. Investments in Debt and Equity Securities Information on investments in debt and equity securities at December 31 is as follows: 2018 2017 Fair Value Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized Gains Losses Gains Losses Corporate notes and bonds $ 4,920 $ 4,985 $ 3 $ (68 ) $ 9,806 $ 9,837 $ 9 $ (40 ) Asset-backed securities 1,275 1,285 1 (11 ) 1,542 1,548 1 (7 ) U.S. government and agency securities 892 895 2 (5 ) 2,042 2,059 — (17 ) Foreign government bonds 166 167 — (1 ) 733 739 — (6 ) Mortgage-backed securities 8 8 — — 626 634 1 (9 ) Commercial paper — — — — 159 159 — — Total debt securities 7,261 7,340 6 (85 ) 14,908 14,976 11 (79 ) Publicly traded equity securities (1) 456 275 265 16 (6 ) Total debt and publicly traded equity securities $ 7,717 $ 15,183 $ 15,241 $ 27 $ (85 ) (1) Pursuant to the adoption of ASU 2016-01 (see Note 2), beginning on January 1, 2018, changes in the fair value of publicly traded equity securities are recognized in net income. Unrealized net losses of $35 million were recognized in Other (income) expense, net during 2018 on equity securities still held at December 31, 2018 . At December 31, 2018 , the Company also had $568 million of equity investments without readily determinable fair values included in Other Assets . During 2018 , the Company recognized unrealized gains of $167 million in Other (income) expense, net on certain of these equity investments based on favorable observable price changes from transactions involving similar investments of the same investee. In addition, during 2018 , the Company recognized unrealized losses of $26 million in Other (income) expense, net related to certain of these investments based on unfavorable observable price changes. Available-for-sale debt securities included in Short-term investments totaled $894 million at December 31, 2018 . Of the remaining debt securities, $5.8 billion mature within five years. At December 31, 2018 and 2017 , there were no debt securities pledged as collateral. Fair Value Measurements Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The Company uses a fair value hierarchy which maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. There are three levels of inputs used to measure fair value with Level 1 having the highest priority and Level 3 having the lowest: Level 1 — Quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity. Level 3 assets or liabilities are those whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques with significant unobservable inputs, as well as assets or liabilities for which the determination of fair value requires significant judgment or estimation. If the inputs used to measure the financial assets and liabilities fall within more than one level described above, the categorization is based on the lowest level input that is significant to the fair value measurement of the instrument. Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis Financial assets and liabilities measured at fair value on a recurring basis at December 31 are summarized below: Fair Value Measurements Using Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total 2018 2017 Assets Investments Corporate notes and bonds $ — $ 4,835 $ — $ 4,835 $ — $ 9,678 $ — $ 9,678 Asset-backed securities (1) — 1,253 — 1,253 — 1,476 — 1,476 U.S. government and agency securities — 731 — 731 68 1,767 — 1,835 Foreign government bonds — 166 — 166 — 732 — 732 Mortgage-backed securities — — — — — 547 — 547 Commercial paper — — — — — 159 — 159 Publicly traded equity securities 147 — — 147 104 — — 104 147 6,985 — 7,132 172 14,359 — 14,531 Other assets (2) U.S. government and agency securities 55 106 — 161 — 207 — 207 Corporate notes and bonds — 85 — 85 — 128 — 128 Asset-backed securities (1) — 22 — 22 — 66 — 66 Mortgage-backed securities — 8 — 8 — 79 — 79 Foreign government bonds — — — — — 1 — 1 Publicly traded equity securities 309 — — 309 171 — — 171 364 221 — 585 171 481 — 652 Derivative assets (3) Forward exchange contracts — 241 — 241 — 48 — 48 Purchased currency options — 213 — 213 — 80 — 80 Interest rate swaps — — — — — 2 — 2 — 454 — 454 — 130 — 130 Total assets $ 511 $ 7,660 $ — $ 8,171 $ 343 $ 14,970 $ — $ 15,313 Liabilities Other liabilities Contingent consideration $ — $ — $ 788 $ 788 $ — $ — $ 935 $ 935 Derivative liabilities (3) Interest rate swaps — 81 — 81 — 55 — 55 Forward exchange contracts — 74 — 74 — 162 — 162 Written currency options — 5 — 5 — — — — — 160 — 160 — 217 — 217 Total liabilities $ — $ 160 $ 788 $ 948 $ — $ 217 $ 935 $ 1,152 (1) Primarily all of the asset-backed securities are highly-rated (Standard & Poor’s rating of AAA and Moody’s Investors Service rating of Aaa), secured primarily by auto loan, credit card and student loan receivables, with weighted-average lives of primarily 5 years or less. (2) Investments included in other assets are restricted as to use, primarily for the payment of benefits under employee benefit plans. (3) The fair value determination of derivatives includes the impact of the credit risk of counterparties to the derivatives and the Company’s own credit risk, the effects of which were not significant. There were no transfers between Level 1 and Level 2 during 2018 . As of December 31, 2018 , Cash and cash equivalents of $8.0 billion include $7.2 billion of cash equivalents (which would be considered Level 2 in the fair value hierarchy). Contingent Consideration Summarized information about the changes in liabilities for contingent consideration is as follows: 2018 2017 Fair value January 1 $ 935 $ 891 Changes in estimated fair value (1) 89 141 Additions 8 3 Payments (244 ) (100 ) Fair value December 31 (2) $ 788 $ 935 (1) Recorded in Research and development expenses, Cost of sales and Other (income) expense, net . Includes cumulative translation adjustments. (2) Balance at December 31, 2018 includes $89 million recorded as a current liability for amounts expected to be paid within the next 12 months. The changes in the estimated fair value of liabilities for contingent consideration in 2018 were largely attributable to increases in the liabilities recorded in connection with the termination of the SPMSD joint venture in 2016 (see Note 9), partially offset by the reversal of a liability related to the discontinuation of a program obtained in connection with the acquisition of SmartCells (see Note 8). The changes in the estimated fair value of liabilities for contingent consideration in 2017 primarily relate to increases in the liabilities recorded in connection with the termination of the SPMSD joint venture and the clinical progression of a program related to the Afferent acquisition. The payments of contingent consideration in 2018 include $175 million related to the achievement of a clinical milestone in connection with the acquisition of Afferent (see Note 3). The remaining payments in 2018 relate to liabilities recorded in connection with the termination of the SPMSD joint venture. The payments of contingent consideration in 2017 relate to the achievement of a clinical milestone in connection with the acquisition of IOmet (see Note 3). Other Fair Value Measurements Some of the Company’s financial instruments, such as cash and cash equivalents, receivables and payables, are reflected in the balance sheet at carrying value, which approximates fair value due to their short-term nature. The estimated fair value of loans payable and long-term debt (including current portion) at December 31, 2018 , was $25.6 billion compared with a carrying value of $25.1 billion and at December 31, 2017 , was $25.6 billion compared with a carrying value of $24.4 billion . Fair value was estimated using recent observable market prices and would be considered Level 2 in the fair value hierarchy. Concentrations of Credit Risk On an ongoing basis, the Company monitors concentrations of credit risk associated with corporate and government issuers of securities and financial institutions with which it conducts business. Credit exposure limits are established to limit a concentration with any single issuer or institution. Cash and investments are placed in instruments that meet high credit quality standards, as specified in the Company’s investment policy guidelines. The majority of the Company’s accounts receivable arise from product sales in the United States and Europe and are primarily due from drug wholesalers and retailers, hospitals, government agencies, managed health care providers and pharmacy benefit managers. The Company monitors the financial performance and creditworthiness of its customers so that it can properly assess and respond to changes in their credit profile. The Company also continues to monitor global economic conditions, including the volatility associated with international sovereign economies, and associated impacts on the financial markets and its business. The Company’s customers with the largest accounts receivable balances are: McKesson Corporation, AmerisourceBergen Corporation and Cardinal Health, Inc., which represented, in aggregate, approximately 40% of total accounts receivable at December 31, 2018 . The Company monitors the creditworthiness of its customers to which it grants credit terms in the normal course of business. Bad debts have been minimal. The Company does not normally require collateral or other security to support credit sales. Derivative financial instruments are executed under International Swaps and Derivatives Association master agreements. The master agreements with several of the Company’s financial institution counterparties also include credit support annexes. These annexes contain provisions that require collateral to be exchanged depending on the value of the derivative assets and liabilities, the Company’s credit rating, and the credit rating of the counterparty. Cash collateral received by the Company from various counterparties was $107 million and $3 million at December 31, 2018 and 2017 , respectively. The obligation to return such collateral is recorded in Accrued and other current liabilities . No cash collateral was advanced by the Company to counterparties as of December 31, 2018 or 2017 .

Inventories

Inventories	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories at December 31 consisted of: 2018 2017 Finished goods $ 1,658 $ 1,334 Raw materials and work in process 5,004 4,703 Supplies 194 201 Total (approximates current cost) 6,856 6,238 Increase to LIFO costs 1 45 $ 6,857 $ 6,283 Recognized as: Inventories $ 5,440 $ 5,096 Other assets 1,417 1,187 Inventories valued under the LIFO method comprised approximately $2.5 billion and $2.2 billion at December 31, 2018 and 2017 , respectively. Amounts recognized as Other assets are comprised almost entirely of raw materials and work in process inventories. At December 31, 2018 and 2017 , these amounts included $1.4 billion and $1.1 billion , respectively, of inventories not expected to be sold within one year. In addition, these amounts included $7 million and $80 million at December 31, 2018 and 2017 , respectively, of inventories produced in preparation for product launches.

Goodwill and Other Intangibles

Goodwill and Other Intangibles	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangibles	Goodwill and Other Intangibles The following table summarizes goodwill activity by segment: Pharmaceutical Animal Health All Other Total Balance January 1, 2017 $ 16,075 $ 1,708 $ 379 $ 18,162 Acquisitions — 177 — 177 Impairments — — (38 ) (38 ) Other (1) (9 ) (8 ) — (17 ) Balance December 31, 2017 (2) 16,066 1,877 341 18,284 Acquisitions — 17 24 41 Impairments — — (144 ) (144 ) Other (1) 96 (24 ) — 72 Balance December 31, 2018 (2) $ 16,162 $ 1,870 $ 221 $ 18,253 (1) Other includes cumulative translation adjustments on goodwill balances and certain other adjustments. (2) Accumulated goodwill impairment losses at December 31, 2018 and 2017 were $369 million and $225 million , respectively. The additions to goodwill within the Animal Health segment in 2017 primarily relate to the acquisition of Vallée (see Note 3). The impairments of goodwill within other non-reportable segments in 2018 and 2017 relate to certain businesses within the Healthcare Services segment. Other intangibles at December 31 consisted of: 2018 2017 Gross Carrying Amount Accumulated Amortization Net Gross Carrying Amount Accumulated Amortization Net Products and product rights $ 46,615 $ 37,585 $ 9,030 $ 46,693 $ 34,950 $ 11,743 IPR&D 1,064 — 1,064 1,194 — 1,194 Tradenames 209 107 102 209 97 112 Other 2,403 1,168 1,235 2,035 901 1,134 $ 50,291 $ 38,860 $ 11,431 $ 50,131 $ 35,948 $ 14,183 Acquired intangibles include products and product rights, tradenames and patents, which are initially recorded at fair value, assigned an estimated useful life, and amortized primarily on a straight-line basis over their estimated useful lives. Some of the Company’s more significant acquired intangibles related to marketed products (included in products and product rights above) at December 31, 2018 include Zerbaxa , $2.7 billion ; Sivextro , $833 million ; Implanon/Nexplanon $470 million ; Dificid , $395 million ; Gardasil/Gardasil 9, $384 million ; Bridion , $275 million ; and Simponi , $194 million . The Company has an intangible asset related to Adempas as a result of a collaboration with Bayer (see Note 4) that had a carrying value of $1.0 billion at December 31, 2018 reflected in “Other” in the table above. During 2017 and 2016 , the Company recorded impairment charges related to marketed products and other intangibles of $58 million and $347 million , respectively, within Cost of sales . During 2017, the Company recorded an intangible asset impairment charge of $47 million related to Intron A , a treatment for certain types of cancers. Sales of Intron A are being adversely affected by the availability of new therapeutic options. In 2017, sales of Intron A in the United States eroded more rapidly than previously anticipated by the Company, which led to changes in the cash flow assumptions for Intron A. These revisions to cash flows indicated that the Intron A intangible asset value was not fully recoverable on an undiscounted cash flows basis. The Company utilized market participant assumptions to determine its best estimate of the fair value of the intangible asset related to Intron A that, when compared with its related carrying value, resulted in the impairment charge noted above. The remaining charges in 2017 relate to the impairment of customer relationship, tradename and developed technology intangibles for certain businesses in the Healthcare Services segment. In 2016, the Company lowered its cash flow projections for Zontivity, a product for the reduction of thrombotic cardiovascular events in patients with a history of myocardial infarction or with peripheral arterial disease, following several business decisions that reduced sales expectations for Zontivity in the United States and Europe. The Company utilized market participant assumptions and considered several different scenarios to determine the fair value of the intangible asset related to Zontivity that, when compared with its related carrying value, resulted in an impairment charge of $252 million . Also during 2016, the Company wrote-off $95 million that had been capitalized in connection with in-licensed products Grastek and Ragwitek, allergy immunotherapy tablets that, for business reasons, the Company returned to the licensor. IPR&D that the Company acquires through business combinations represents the fair value assigned to incomplete research projects which, at the time of acquisition, have not reached technological feasibility. Amounts capitalized as IPR&D are accounted for as indefinite-lived intangible assets, subject to impairment testing until completion or abandonment of the projects. Upon successful completion of each project, the Company will make a separate determination as to the then useful life of the asset and begin amortization. In 2018, the Company recorded $152 million of IPR&D impairment charges within Research and development expenses. Of this amount, $139 million relates to the write-off of the remaining intangible asset balance for a program obtained in connection with the SmartCells acquisition following a decision to terminate the program due to product development issues. The Company previously recorded an impairment charge in 2016 for the other programs obtained in connection with the acquisition of SmartCells as described below. The discontinuation of this clinical development program resulted in a reversal of the related liability for contingent consideration of $60 million (see Note 6). In 2017, the Company recorded $483 million of IPR&D impairment charges. Of this amount, $240 million resulted from a strategic decision to discontinue the development of the investigational combination regimens MK-3682B (grazoprevir/ruzasvir/uprifosbuvir) and MK-3682C (ruzasvir/uprifosbuvir) for the treatment of chronic hepatitis C virus (HCV) infection. This decision was made based on a review of available Phase 2 efficacy data and in consideration of the evolving marketplace and the growing number of treatment options available for patients with chronic HCV infection, including Zepatier , which is marketed by the Company for the treatment of adult patients with chronic HCV infection. As a result of this decision, the Company recorded an IPR&D impairment charge to write-off the remaining intangible asset related to uprifosbuvir. The Company had previously recorded an impairment charge for uprifosbuvir in 2016 as described below. The IPR&D impairment charges in 2017 also include a charge of $226 million to write-off the intangible asset related to verubecestat, an investigational small molecule inhibitor of the beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), resulting from a decision in February 2018 to stop a Phase 3 study evaluating verubecestat in people with prodromal Alzheimer’s disease. The decision to stop the study followed a recommendation by the external Data Monitoring Committee (eDMC), which assessed overall benefit/risk during an interim safety analysis. The eDMC concluded that it was unlikely that positive benefit/risk could be established if the trial continued. During 2016, the Company recorded $3.6 billion of IPR&D impairment charges. Of this amount, $2.9 billion related to the clinical development program for uprifosbuvir, a nucleotide prodrug that was being evaluated for the treatment of HCV. The Company determined that changes to the product profile, as well as changes to Merck’s expectations for pricing and the market opportunity, taken together constituted a triggering event that required the Company to evaluate the uprifosbuvir intangible asset for impairment. Utilizing market participant assumptions, and considering different scenarios, the Company concluded that its best estimate of the fair value of the intangible asset related to uprifosbuvir was $240 million , resulting in the recognition of the impairment charge noted above. The IPR&D impairment charges in 2016 also included charges of $180 million and $143 million related to the discontinuation of programs obtained in connection with the acquisitions of cCAM Biotherapeutics Ltd. and OncoEthix, respectively, resulting from unfavorable efficacy data. An additional $72 million related to programs obtained in connection with the SmartCells acquisition following a decision to terminate the lead compound due to a lack of efficacy and to pursue a back-up compound which reduced projected future cash flows. The IPR&D impairment charges in 2016 also included $112 million related to an in-licensed program for house dust mite allergies that, for business reasons, was returned to the licensor. The remaining IPR&D impairment charges in 2016 primarily related to deprioritized pipeline programs that were deemed to have no alternative use during the period, including a $79 million impairment charge for an investigational candidate for contraception. The discontinuation or delay of certain of these clinical development programs resulted in a reduction of the related liabilities for contingent consideration. The IPR&D projects that remain in development are subject to the inherent risks and uncertainties in drug development and it is possible that the Company will not be able to successfully develop and complete the IPR&D programs and profitably commercialize the underlying product candidates. The Company may recognize additional non-cash impairment charges in the future related to other marketed products or pipeline programs and such charges could be material. Aggregate amortization expense primarily recorded within Cost of sales was $2.9 billion in 2018 , $3.2 billion in 2017 and $3.8 billion in 2016 . The estimated aggregate amortization expense for each of the next five years is as follows: 2019 , $1.5 billion ; 2020 , $1.2 billion ; 2021 , $1.1 billion ; 2022 , $1.1 billion ; 2023 , $1.1 billion .

Joint Ventures and Other Equity

Joint Ventures and Other Equity Method Affiliates	12 Months Ended
	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Joint Ventures and Other Equity Method Affiliates	Joint Ventures and Other Equity Method Affiliates Sanofi Pasteur MSD In 1994, Merck and Pasteur Mérieux Connaught (now Sanofi Pasteur S.A.) established an equally-owned joint venture (SPMSD) to market vaccines in Europe and to collaborate in the development of combination vaccines for distribution in Europe. Joint venture vaccine sales were $1.0 billion for 2016. On December 31, 2016, Merck and Sanofi Pasteur (Sanofi) terminated SPMSD and ended their joint vaccines operations in Europe. Under the terms of the termination, Merck acquired Sanofi’s 50% interest in SPMSD in exchange for consideration of $657 million comprised of cash, as well as future royalties of 11.5% on net sales of all Merck products that were previously sold by the joint venture through December 31, 2024, which the Company determined had a fair value of $416 million on the date of termination. The Company accounted for this transaction as a step acquisition, which required that Merck remeasure its ownership interest (previously accounted for as an equity method investment) to fair value at the acquisition date. Merck in turn sold to Sanofi its intellectual property rights held by SPMSD in exchange for consideration of $596 million comprised of cash and future royalties of 11.5% on net sales of all Sanofi products that were previously sold by the joint venture through December 31, 2024, which the Company determined had a fair value of $302 million on the date of termination. Excluded from this arrangement are sales of Vaxelis (a jointly developed pediatric hexavalent combination vaccine that was approved by the European Commission in 2016 and by the U.S. Food and Drug Administration in 2018). The European marketing rights for Vaxelis were transferred to a separate equally-owned joint venture between Sanofi and Merck. The net impact of the termination of the SPMSD joint venture is as follows: Products and product rights (8-year useful life) $ 936 Accounts receivable 133 Income taxes payable (221 ) Deferred income tax liabilities (147 ) Other, net 47 Net assets acquired 748 Consideration payable to Sanofi, net (392 ) Derecognition of Merck’s previously held equity investment in SPMSD (183 ) Increase in net assets 173 Merck’s share of restructuring costs related to the termination (77 ) Net gain on termination of SPMSD joint venture (1) $ 96 (1) Recorded in Other (income) expense, net . The estimated fair values of identifiable intangible assets related to products and product rights were determined using an income approach through which fair value is estimated based on market participant expectations of each asset’s projected net cash flows. The projected net cash flows were then discounted to present value utilizing a discount rate of 11.5% . Actual cash flows are likely to be different than those assumed. Of the amount recorded for products and product rights, $468 million related to Gardasil/Gardasil 9. The fair value of liabilities for contingent consideration related to Merck’s future royalty payments to Sanofi of $416 million (reflected in the consideration payable to Sanofi, net, in the table above) was determined at the acquisition date using unobservable inputs. These inputs include the estimated amount and timing of projected cash flows and a risk-adjusted discount rate of 8% used to present value the cash flows. Changes in the inputs could result in a different fair value measurement. Based on an existing accounting policy election, Merck did not record the $302 million estimated fair value of contingent future royalties to be received from Sanofi on the sale of Sanofi products, but rather is recognizing such amounts as sales occur and the royalties are earned. The Company incurred $24 million of transaction costs related to the termination of SPMSD included in Selling, general and administrative expenses in 2016. Pro forma financial information for this transaction has not been presented as the results are not significant when compared with the Company’s financial results. AstraZeneca LP In 1982, Merck entered into an agreement with Astra AB (Astra) to develop and market Astra products under a royalty-bearing license. In 1993, Merck’s total sales of Astra products reached a level that triggered the first step in the establishment of a joint venture business carried on by Astra Merck Inc. (AMI), in which Merck and Astra each owned a 50% share. This joint venture, formed in 1994, developed and marketed most of Astra’s new prescription medicines in the United States. In 1998, Merck and Astra completed a restructuring of the ownership and operations of the joint venture whereby Merck acquired Astra’s interest in AMI, renamed KBI Inc. (KBI), and contributed KBI’s operating assets to a new U.S. limited partnership, Astra Pharmaceuticals L.P. (the Partnership), in exchange for a 1% limited partner interest. Astra contributed the net assets of its wholly owned subsidiary, Astra USA, Inc., to the Partnership in exchange for a 99% general partner interest. The Partnership, renamed AstraZeneca LP (AZLP) upon Astra’s 1999 merger with Zeneca Group Plc, became the exclusive distributor of the products for which KBI retained rights. Merck earned revenue based on sales of KBI products and earned certain Partnership returns from AZLP. On June 30, 2014, AstraZeneca exercised its option to purchase Merck’s interest in KBI (and redeem Merck’s remaining interest in AZLP). A portion of the exercise price, which remained subject to a true-up in 2018 based on actual sales of Nexium and Prilosec from closing in 2014 to June 2018, was deferred and recognized as income as the contingency was eliminated as sales occurred. Once the deferred income amount was fully recognized, in 2016, the Company began recognizing income and a corresponding receivable for amounts that would be due to Merck from AstraZeneca based on the sales performance of Nexium and Prilosec subject to the true-up in June 2018. The Company recognized income of $99 million in 2018, $232 million in 2017, and $98 million in 2016 (including $5 million of remaining deferred income) in Other (income) expense, net related to these amounts. In January 2019, the Company received $424 million from AstraZeneca in settlement of these amounts, which concludes the transactions related to the 2014 termination of Company’s relationship with AZLP.

Loans Payable, Long-Term Debt a

Loans Payable, Long-Term Debt and Other Commitments	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Loans Payable, Long-Term Debt and Other Commitments	Loans Payable, Long-Term Debt and Other Commitments Loans payable at December 31, 2018 included $5.1 billion of commercial paper and $149 million of long-dated notes that are subject to repayment at the option of the holders. Loans payable at December 31, 2017 included $3.0 billion of notes due in 2018 and $73 million of long-dated notes that are subject to repayment at the option of the holders. The weighted-average interest rate of commercial paper borrowings was 2.09% and 0.85% for the years ended December 31, 2018 and 2017 , respectively. Long-term debt at December 31 consisted of: 2018 2017 2.75% notes due 2025 $ 2,490 $ 2,488 3.70% notes due 2045 1,974 1,973 2.80% notes due 2023 1,745 1,744 4.15% notes due 2043 1,237 1,237 1.85% notes due 2020 1,231 1,232 2.35% notes due 2022 1,214 1,220 1.125% euro-denominated notes due 2021 1,134 1,185 3.875% notes due 2021 1,132 1,140 1.875% euro-denominated notes due 2026 1,127 1,178 2.40% notes due 2022 983 993 6.50% notes due 2033 726 729 Floating-rate notes due 2020 699 699 0.50% euro-denominated notes due 2024 565 591 1.375% euro-denominated notes due 2036 561 587 2.50% euro-denominated notes due 2034 560 585 3.60% notes due 2042 490 489 6.55% notes due 2037 414 415 5.75% notes due 2036 338 338 5.95% debentures due 2028 306 306 5.85% notes due 2039 270 270 6.40% debentures due 2028 250 250 6.30% debentures due 2026 135 135 5.00% notes due 2019 — 1,260 Other 225 309 $ 19,806 $ 21,353 Other (as presented in the table above) includes $223 million and $300 million at December 31, 2018 and 2017 , respectively, of borrowings at variable rates that resulted in effective interest rates of 2.27% and 1.42% for 2018 and 2017 , respectively. With the exception of the 6.30% debentures due 2026, the notes listed in the table above are redeemable in whole or in part, at Merck’s option at any time, at varying redemption prices. In December 2018, the Company exercised a make-whole provision on its $1.25 billion , 5.00% notes due 2019 and repaid this debt. In November 2017, the Company launched tender offers for certain outstanding notes and debentures. The Company paid $810 million in aggregate consideration (applicable purchase price together with accrued interest) to redeem $585 million principal amount of debt that was validly tendered in connection with the tender offers and recognized a loss on extinguishment of debt of $191 million in 2017. Effective as of November 3, 2009, the Company executed a full and unconditional guarantee of the then existing debt of its subsidiary Merck Sharp & Dohme Corp. (MSD) and MSD executed a full and unconditional guarantee of the then existing debt of the Company (excluding commercial paper), including for payments of principal and interest. These guarantees do not extend to debt issued subsequent to that date. Certain of the Company’s borrowings require that Merck comply with covenants and, at December 31, 2018 , the Company was in compliance with these covenants. The aggregate maturities of long-term debt for each of the next five years are as follows: 2019 , no maturities; 2020 , $1.9 billion ; 2021 , $2.3 billion ; 2022 , $2.2 billion ; 2023 , $1.7 billion . The Company has a $6.0 billion credit facility that matures in June 2023. The facility provides backup liquidity for the Company’s commercial paper borrowing facility and is to be used for general corporate purposes. The Company has not drawn funding from this facility. Rental expense under operating leases, net of sublease income, was $322 million in 2018 , $327 million in 2017 and $292 million in 2016 . The minimum aggregate rental commitments under noncancellable leases are as follows: 2019 , $188 million ; 2020 , $198 million ; 2021 , $150 million ; 2022 , $134 million ; 2023 , $84 million and thereafter, $243 million . The Company has no significant capital leases.

Contingencies and Environmental

Contingencies and Environmental Liabilities	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Environmental Liabilities	Contingencies and Environmental Liabilities The Company is involved in various claims and legal proceedings of a nature considered normal to its business, including product liability, intellectual property, and commercial litigation, as well as certain additional matters including governmental and environmental matters. In the opinion of the Company, it is unlikely that the resolution of these matters will be material to the Company’s financial position, results of operations or cash flows. Given the nature of the litigation discussed below and the complexities involved in these matters, the Company is unable to reasonably estimate a possible loss or range of possible loss for such matters until the Company knows, among other factors, (i) what claims, if any, will survive dispositive motion practice, (ii) the extent of the claims, including the size of any potential class, particularly when damages are not specified or are indeterminate, (iii) how the discovery process will affect the litigation, (iv) the settlement posture of the other parties to the litigation and (v) any other factors that may have a material effect on the litigation. The Company records accruals for contingencies when it is probable that a liability has been incurred and the amount can be reasonably estimated. These accruals are adjusted periodically as assessments change or additional information becomes available. For product liability claims, a portion of the overall accrual is actuarially determined and considers such factors as past experience, number of claims reported and estimates of claims incurred but not yet reported. Individually significant contingent losses are accrued when probable and reasonably estimable. Legal defense costs expected to be incurred in connection with a loss contingency are accrued when probable and reasonably estimable. The Company’s decision to obtain insurance coverage is dependent on market conditions, including cost and availability, existing at the time such decisions are made. The Company has evaluated its risks and has determined that the cost of obtaining product liability insurance outweighs the likely benefits of the coverage that is available and, as such, has no insurance for most product liabilities effective August 1, 2004. Product Liability Litigation Fosamax As previously disclosed, Merck is a defendant in product liability lawsuits in the United States involving Fosamax ( Fosamax Litigation). As of December 31, 2018 , approximately 3,900 cases have been filed and either are pending or conditionally dismissed (as noted below) against Merck in either federal or state court. Plaintiffs in the vast majority of these cases generally allege that they sustained femur fractures and/or other bone injuries (Femur Fractures) in association with the use of Fosamax . In March 2011, Merck submitted a Motion to Transfer to the Judicial Panel on Multidistrict Litigation (JPML) seeking to have all federal cases alleging Femur Fractures consolidated into one multidistrict litigation for coordinated pre-trial proceedings. All federal cases involving allegations of Femur Fracture have been or will be transferred to a multidistrict litigation in the District of New Jersey (Femur Fracture MDL). In the only bellwether case tried to date in the Femur Fracture MDL, Glynn v. Merck , the jury returned a verdict in Merck’s favor. In addition, in June 2013, the Femur Fracture MDL court granted Merck’s motion for judgment as a matter of law in the Glynn case and held that the plaintiff’s failure to warn claim was preempted by federal law. In August 2013, the Femur Fracture MDL court entered an order requiring plaintiffs in the Femur Fracture MDL to show cause why those cases asserting claims for a femur fracture injury that took place prior to September 14, 2010, should not be dismissed based on the court’s preemption decision in the Glynn case. Pursuant to the show cause order, in March 2014, the Femur Fracture MDL court dismissed with prejudice approximately 650 cases on preemption grounds. Plaintiffs in approximately 515 of those cases appealed that decision to the U.S. Court of Appeals for the Third Circuit (Third Circuit). In March 2017, the Third Circuit issued a decision reversing the Femur Fracture MDL court’s preemption ruling and remanding the appealed cases back to the Femur Fracture MDL court. Merck filed a petition for a writ of certiorari to the U.S. Supreme Court in August 2017, seeking review of the Third Circuit’s decision. In December 2017, the Supreme Court invited the Solicitor General to file a brief in the case expressing the views of the United States, and in May 2018, the Solicitor General submitted a brief stating that the Third Circuit’s decision was wrongly decided and recommended that the Supreme Court grant Merck’s cert petition. The Supreme Court granted Merck’s petition in June 2018, and an oral argument before the Supreme Court was held on January 7, 2019. The final decision on the Femur Fracture MDL court’s preemption ruling is now pending before the Supreme Court. Accordingly, as of December 31, 2018 , nine cases were actively pending in the Femur Fracture MDL, and approximately 1,055 cases have either been dismissed without prejudice or administratively closed pending final resolution by the Supreme Court of the appeal of the Femur Fracture MDL court’s preemption order. As of December 31, 2018 , approximately 2,555 cases alleging Femur Fractures have been filed in New Jersey state court and are pending before Judge James Hyland in Middlesex County. The parties selected an initial group of 30 cases to be reviewed through fact discovery. Two additional groups of 50 cases each to be reviewed through fact discovery were selected in November 2013 and March 2014, respectively. A further group of 25 cases to be reviewed through fact discovery was selected by Merck in July 2015, and Merck has continued to select additional cases to be reviewed through fact discovery from 2016 to the present. As of December 31, 2018 , approximately 275 cases alleging Femur Fractures have been filed and are pending in California state court. All of the Femur Fracture cases filed in California state court have been coordinated before a single judge in Orange County, California. In March 2014, the court directed that a group of 10 discovery pool cases be reviewed through fact discovery and subsequently scheduled the Galper v. Merck case, which plaintiffs selected, as the first trial. The Galper trial began in February 2015 and the jury returned a verdict in Merck’s favor in April 2015, and plaintiff appealed that verdict to the California appellate court. In April 2017, the California appellate court issued a decision affirming the lower court’s judgment in favor of Merck. The next Femur Fracture trial in California that was scheduled to begin in April 2016 was stayed at plaintiffs’ request and a new trial date has not been set. Additionally, there are four Femur Fracture cases pending in other state courts. Discovery is ongoing in the Femur Fracture MDL and in state courts where Femur Fracture cases are pending and the Company intends to defend against these lawsuits. Januvia/Janumet As previously disclosed, Merck is a defendant in product liability lawsuits in the United States involving Januvia and/or Janumet . As of December 31, 2018 , Merck is aware of approximately 1,290 product users alleging that Januvia and/or Janumet caused the development of pancreatic cancer and other injuries. Most claims have been filed in multidistrict litigation before the U.S. District Court for the Southern District of California (MDL). Outside of the MDL, the majority of claims have been filed in coordinated proceedings before the Superior Court of California, County of Los Angeles (California State Court). In November 2015, the MDL and California State Court-in separate opinions-granted summary judgment to defendants on grounds of federal preemption. Plaintiffs appealed in both forums. In November 2017, the U.S. Court of Appeals for the Ninth Circuit vacated the judgment and remanded for further discovery, which is ongoing. In November 2018, the California state appellate court reversed and remanded on similar grounds. As of December 31, 2018 , eight product users have claims pending against Merck in state courts other than California, including Illinois. In June 2017, the Illinois trial court denied Merck’s motion for summary judgment based on federal preemption. Merck appealed, and the Illinois appellate court affirmed in December 2018. Merck intends to appeal that ruling. In addition to the claims noted above, the Company has agreed to toll the statute of limitations for approximately 50 additional claims. The Company intends to continue defending against these lawsuits. Vioxx As previously disclosed, Merck is a defendant in a lawsuit brought by the Attorney General of Utah alleging that Merck misrepresented the safety of Vioxx . The lawsuit is pending in Utah state court. Utah seeks damages and penalties under the Utah False Claims Act. A bench trial in this matter is currently scheduled for July 2019. Propecia/Proscar As previously disclosed, Merck is a defendant in product liability lawsuits in the United States involving Propecia and/or Proscar . The lawsuits were filed in various federal courts and in state court in New Jersey. The federal lawsuits were then consolidated for pretrial purposes in a federal multidistrict litigation before Judge Brian Cogan of the Eastern District of New York. The matters pending in state court in New Jersey were consolidated before Judge Hyland in Middlesex County (NJ Coordinated Proceedings). As previously disclosed, on April 9, 2018, Merck and the Plaintiffs’ Executive Committee in the Propecia MDL and the Plaintiffs’ Liaison Counsel in the NJ Coordinated Proceedings entered into an agreement to resolve the above mentioned Propecia/Proscar lawsuits for an aggregate amount of $4.3 million . The settlement was subject to certain contingencies, including 95% plaintiff participation and a per plaintiff clawback if the participation rate was less than 100%. The contingencies were satisfied and the settlement agreement was finalized. After the settlement, fewer than 25 cases remain pending in the United States. The Company intends to defend against any remaining unsettled lawsuits. Governmental Proceedings As previously disclosed, the Company has learned that the Prosecution Office of Milan, Italy is investigating interactions between the Company’s Italian subsidiary, certain employees of the subsidiary and certain Italian health care providers. The Company understands that this is part of a larger investigation involving engagements between various health care companies and those health care providers. The Company is cooperating with the investigation. As previously disclosed, the United Kingdom (UK) Competition and Markets Authority (CMA) issued a Statement of Objections against the Company and MSD Sharp & Dohme Limited (MSD UK) in May 2017. In the Statement of Objections, the CMA alleges that MSD UK abused a dominant position through a discount program for Remicade over the period from March 2015 to February 2016. The Company and MSD UK are contesting the CMA’s allegations. As previously disclosed, the Company has received an investigative subpoena from the California Insurance Commissioner’s Fraud Bureau (Bureau) seeking information from January 1, 2007 to the present related to the pricing and promotion of Cubicin . The Bureau is investigating whether Cubist Pharmaceuticals, Inc., which the Company acquired in 2015, unlawfully induced the presentation of false claims for Cubicin to private insurers under the California Insurance Code False Claims Act. The Company is cooperating with the investigation. As previously disclosed, the Company’s subsidiaries in China have received and may continue to receive inquiries regarding their operations from various Chinese governmental agencies. Some of these inquiries may be related to matters involving other multinational pharmaceutical companies, as well as Chinese entities doing business with such companies. The Company’s policy is to cooperate with these authorities and to provide responses as appropriate. As previously disclosed, from time to time, the Company receives inquiries and is the subject of preliminary investigation activities from competition and other governmental authorities in markets outside the United States. These authorities may include regulators, administrative authorities, and law enforcement and other similar officials, and these preliminary investigation activities may include site visits, formal or informal requests or demands for documents or materials, inquiries or interviews and similar matters. Certain of these preliminary inquiries or activities may lead to the commencement of formal proceedings. Should those proceedings be determined adversely to the Company, monetary fines and/or remedial undertakings may be required. Commercial and Other Litigation Zetia Antitrust Litigation As previously disclosed, Merck, MSD, Schering Corporation and MSP Singapore Company LLC (collectively, the Merck Defendants) are defendants in putative class action and opt-out lawsuits filed in 2018 on behalf of direct and indirect purchasers of Zetia alleging violations of federal and state antitrust laws, as well as other state statutory and common law causes of action. The cases have been consolidated for pretrial purposes in a federal multidistrict litigation before Judge Rebecca Beach Smith in the Eastern District of Virginia. On December 6, 2018, the court denied the Merck Defendants’ motions to dismiss or stay the direct purchaser putative class actions pending bilateral arbitration. On February 6, 2019, the magistrate judge issued a report and recommendation recommending that the district judge grant in part and deny in part defendants’ motions to dismiss on non-arbitration issues. On February 20, 2019, defendants and retailer opt-out plaintiffs filed objections to the report and recommendation. After responses are filed, the parties will await a decision from the district judge. Rotavirus Vaccines Antitrust Litigation As previously disclosed, MSD is a defendant in putative class action lawsuits filed in 2018 on behalf of direct purchasers of RotaTeq , alleging violations of federal antitrust laws. The cases were consolidated in the Eastern District of Pennsylvania. On January 23, 2019, the court denied MSD’s motions to compel arbitration and to dismiss the consolidated complaint. On February 19, 2019, MSD appealed the court’s order on arbitration to the Third Circuit, and on February 22, 2019, the court granted MSD’s motion to vacate existing deadlines in the district court in light of the appeal. Sales Force Litigation As previously disclosed, in May 2013, Ms. Kelli Smith filed a complaint against the Company in the U.S. District Court for the District of New Jersey on behalf of herself and a putative class of female sales representatives and a putative sub-class of female sales representatives with children, claiming (a) discriminatory policies and practices in selection, promotion and advancement, (b) disparate pay, (c) differential treatment, (d) hostile work environment and (e) retaliation under federal and state discrimination laws. In January 2014, plaintiffs filed an amended complaint adding four additional named plaintiffs. In October 2014, the court denied the Company’s motion to dismiss or strike the class claims as premature. In September 2015, plaintiffs filed additional motions, including a motion for conditional certification under the Equal Pay Act; a motion to amend the pleadings seeking to add ERISA and constructive discharge claims and a Company subsidiary as a named defendant; and a motion for equitable relief. Merck filed papers in opposition to the motions. In April 2016, the court granted plaintiff’s motion for conditional certification but denied plaintiffs’ motions to extend the liability period for their Equal Pay Act claims back to June 2009. In April 2016, the Magistrate Judge granted plaintiffs’ request to amend the complaint to add the following: (i) a Company subsidiary as a corporate defendant; (ii) an ERISA claim and (iii) an individual constructive discharge claim for one of the named plaintiffs. Approximately 700 individuals opted-in to this action; the opt-in period has closed. In August 2017, plaintiffs filed their motion for class certification. This motion sought to certify a Title VII pay discrimination class and also sought final collective action certification of plaintiffs’ Equal Pay Act claim. On October 1, 2018, the parties entered into an agreement to fully resolve the Smith sales force litigation. As part of the settlement and in exchange for a full and general release of all individual and class claims, the Company agreed to pay $8.5 million . The settlement agreement, which contains an “opt-out” clause allowing Merck to pull out of the agreement if 30 or more individuals opt out, will be subject to court approval. On December 18, 2018, plaintiffs filed a motion with the court seeking preliminary approval of the settlement. Qui Tam Litigation As previously disclosed, in June 2012, the U.S. District Court for the Eastern District of Pennsylvania unsealed a complaint that has been filed against the Company under the federal False Claims Act by two former employees alleging, among other things, that the Company defrauded the U.S. government by falsifying data in connection with a clinical study conducted on the mumps component of the Company’s M-M-R II vaccine. The complaint alleges the fraud took place between 1999 and 2001. The U.S. government had the right to participate in and take over the prosecution of this lawsuit, but notified the court that it declined to exercise that right. The two former employees are pursuing the lawsuit without the involvement of the U.S. government. In addition, as previously disclosed, two putative class action lawsuits on behalf of direct purchasers of the M‑M‑R II vaccine, which charge that the Company misrepresented the efficacy of the M-M-R II vaccine in violation of federal antitrust laws and various state consumer protection laws, are pending in the Eastern District of Pennsylvania. In September 2014, the court denied Merck’s motion to dismiss the False Claims Act suit and granted in part and denied in part its motion to dismiss the then-pending antitrust suit. As a result, both the False Claims Act suit and the antitrust suits have proceeded into discovery, which is ongoing. The Company continues to defend against these lawsuits. Merck KGaA Litigation As previously disclosed, in January 2016, to protect its long-established brand rights in the United States, the Company filed a lawsuit against Merck KGaA, Darmstadt, Germany (KGaA), historically operating as the EMD Group in the United States, alleging it improperly uses the name “Merck” in the United States. KGaA has filed suit against the Company in France, the UK, Germany, Switzerland, Mexico, India, Australia, Singapore, Hong Kong, and China alleging, among other things, unfair competition, trademark infringement and/or corporate name infringement. In the UK, Australia, Singapore, Hong Kong, and India, KGaA also alleges breach of the parties’ coexistence agreement. In December 2015, the Paris Court of First Instance issued a judgment finding that certain activities by the Company directed towards France did not constitute trademark infringement and unfair competition while other activities were found to infringe and constitute unfair competition. The Company and KGaA appealed the decision, and the appeal was heard in May 2017. In June 2017, the French appeals court held that certain of the activities by the Company directed to France constituted unfair competition or trademark infringement and, in December 2017, the Company decided not to pursue any further appeal. In January 2016, the UK High Court issued a judgment finding that the Company had breached the co-existence agreement and infringed KGaA’s trademark rights as a result of certain activities directed towards the UK based on use of the word MERCK on promotional and information activity. As noted in the UK decision, this finding was not based on the Company’s use of the sign MERCK in connection with the sale of products or any material pharmaceutical business transacted in the UK. The Company and KGaA have both appealed this decision, and the appeal was heard in June 2017. In November 2017, the UK Court of Appeals affirmed the decision on the co-existence agreement and remitted for re-hearing issues of trademark infringement, the scope of KGaA’s UK trademarks for pharmaceutical products, and the relief to which KGaA would be entitled. The re-hearing was held, and no decision has been handed down. In November 2018, the District Court in Hamburg, Germany dismissed all of KGaA’s claims concerning KGaA’s EU trademark with respect to the territory of the EU. In accordance with the Judgment of the Court of Justice of the EU delivered in October 2017, the District Court in Hamburg further held that it had no jurisdiction over the claim by KGaA insofar as the claim related to the territory of the UK. KGaA has appealed this decision. Further decisions from the District Court in Hamburg, Germany, in connection with claims concerning KGaA’s EU trademark, German trademark and trade name rights as well as unfair competition law with respect to the territory of Germany are expected on February 28, 2019. In January 2019, the Mexican Trademark Office issued a decision on KGaA’s action. The court found no trademark infringement by the Company and dismissed all of KGaA’s claims for trademark infringement. The court ruled against the Company on KGaA’s unfair competition claim. Both KGaA and the Company have appealed this decision. Patent Litigation From time to time, generic manufacturers of pharmaceutical products file abbreviated NDAs with the FDA seeking to market generic forms of the Company’s products prior to the expiration of relevant patents owned by the Company. To protect its patent rights, the Company may file patent infringement lawsuits against such generic companies. Similar lawsuits defending the Company’s patent rights may exist in other countries. The Company intends to vigorously defend its patents, which it believes are valid, against infringement by companies attempting to market products prior to the expiration of such patents. As with any litigation, there can be no assurance of the outcomes, which, if adverse, could result in significantly shortened periods of exclusivity for these products and, with respect to products acquired through acquisitions, potentially significant intangible asset impairment charges. Inegy — The patents protecting Inegy in Europe have expired but supplemental protection certificates (SPCs) have been granted to the Company in many European countries that will expire in April 2019. There are multiple challenges to the SPCs related to Inegy throughout Europe and generic products have been launched in Austria, France, Italy, Ireland, Spain, Portugal, Germany, and the Netherlands. The Company has filed for preliminary injunctions in many countries that are still pending decision. Preliminary injunctions are presently in force in Austria, Czech Republic, Greece, Norway, Portugal, and Slovakia. Preliminary injunctions have been denied or revoked in Germany, Ireland, the Netherlands and Spain. The Company is appealing those decisions. In France and Belgium, preliminary injunctions were granted against some companies and denied against others, and appeals are pending. The SPC was held valid in merits proceedings in Portugal and France. The Company has filed and will continue to file actions for patent infringement seeking damages against those companies that launch generic products before April 2019. Noxafil — In August 2015, the Company filed a lawsuit against Actavis Laboratories Fl, Inc. (Actavis) in the United States in respect of that company’s application to the FDA seeking pre-patent expiry approval to sell a generic version of Noxafil . In October 2017, the district court held the patent valid and infringed. Actavis appealed this decision. While the appeal was pending, the parties reached a settlement, subject to certain terms of the agreement being met, whereby Actavis can launch its generic version prior to expiry of the patent and pediatric exclusivity under certain conditions. In March 2016, the Company filed a lawsuit against Roxane Laboratories, Inc. (Roxane) in the United States in respect of that company’s application to the FDA seeking pre-patent expiry approval to sell a generic version of Noxafil . In November 2017, the parties reached a settlement whereby Roxane can launch its generic version prior to expiry of the patent under certain conditions. In February 2016, the Company filed a lawsuit against Par Sterile Products LLC, Par Pharmaceutical, Inc., Par Pharmaceutical Companies, Inc. and Par Pharmaceutical Holdings, Inc. (collectively, Par) in the United States in respect of that company’s application to the FDA seeking pre-patent expiry approval to sell a generic version of Noxafil injection. In October 2016, the parties reached a settlement whereby Par can launch its generic version in January 2023, or earlier under certain conditions. In February 2018, the Company filed a lawsuit against Fresenius Kabi USA, LLC (Fresenius) in the United States in respect of that company’s application to the FDA seeking pre-patent expiry approval to sell a generic version of Noxafil . In November 2018, the Company reached a settlement with Fresenius, whereby Fresenius can launch its generic version of the intravenous product prior to expiry of the patent under certain conditions. In March 2018, the Company filed a lawsuit against Mylan Laboratories Limited in the United States in respect of that company’s application to the FDA seeking pre-patent expiry approval to sell a generic version of Noxafil . Nasonex — Nasonex lost market exclusivity in the United States in 2016. Prior to that, in April 2015, the Company filed a patent infringement lawsuit against Apotex Inc. and Apotex Corp. (Apotex) in respect of Apotex’s marketed product that the Company believed was infringing. In January 2018, the Company and Apotex settled this matter with Apotex agreeing to pay the Company $115 million plus certain other consideration. Januvia, Janumet, Janumet XR — In February 2019, Par Pharmaceutical, Inc. (Par Pharmaceutical) filed suit against the Company in the U.S. District Court for the District of New Jersey, seeking a declaratory judgment of invalidity of a patent owned by the Company covering certain salt and polymorphic forms of sitagliptin that expires in 2026. A judgment in its favor may allow Par Pharmaceutical to bring to market a generic version of Janumet XR following the expiration of key patent protection in 2022, but prior to the expiration of the later-granted patent it is challenging. In response, the Company filed a patent infringement lawsuit in the U.S. District Court for the District of Delaware against Par Pharmaceutical and additional companies that also indicated an intent to market generic versions of Januvia , Janumet , and Janumet XR following expiration of key patent protection in 2022, but prior to the expiration of the later-granted patent owned by the Company covering certain salt and polymorphic forms of sitagliptin that expires in 2026, and a later granted patent owned by the Company covering the Janumet formulation which expires in 2028. No schedule for the cases has been set by the court. Gilead Patent Litigation and Opposition The Company, through its Idenix Pharmaceuticals, Inc. subsidiary, has pending litigation against Gilead in the United States, Germany, and France based on different patent estates that would be infringed by Gilead’s sales of their two products, Sovaldi and Harvoni. Gilead opposed the European patent at the European Patent Office (EPO). Trial in the United States was held in December 2016 and the jury returned a verdict for the Company, awarding damages of $2.54 billion . The Company submitted post-trial motions, including on the issues of enhanced damages and future royalties. Gilead submitted post-trial motions for judgment as a matter of law. A hearing on the motions was held in September 2017. Also, in September 2017, the court denied the Company’s motion on enhanced damages, granted its motion on prejudgment interest and deferred its motion on future royalties. In February 2018, the court granted Gilead’s motion for judgment as a matter of law and found the patent was invalid for a lack of enablement. The Company appealed this decision. The appellate briefing is completed and the Company is waiting for the oral argument to be scheduled. The EPO opposition division revoked the European patent, and the Company appealed this decision. The cases in France and Germany have been stayed pending the final decision of the EPO. Other Litigation There are various other pending legal proceedings involving the Company, principally product liability and intellectual property lawsuits. While it is not feasible to predict the outcome of such proceedings, in the opinion of the Company, either the likelihood of loss is remote or any reasonably possible loss associated with the resolution of such proceedings is not expected to be material to the Company’s financial position, results of operations or cash flows either individually or in the aggregate. Legal Defense Reserves Legal defense costs expected to be incurred in connection with a loss contingency are accrued when probable and reasonably estimable. Some of the significant factors considered in the review of these legal defense reserves are as follows: the actual costs incurred by the Company; the development of the Company’s legal defense strategy and structure in light of the scope of its litigation; the number of cases being brought against the Company; the costs and outcomes of completed trials and the most current information regarding anticipated timing, progression, and related costs of pre-trial activities and trials in the associated litigation. The amount of legal defense reserves as of December 31, 2018 and 2017 of approximately $245 million and $160 million , respectively, represents the Company’s best estimate of the minimum amount of defense costs to be incurred in connection with its outstanding litigation; however, events such as additional trials and other events that could arise in the course of its litigation could affect the ultimate amount of legal defense costs to be incurred by the Company. The Company will continue to monitor its legal defense costs and review the adequacy of the associated reserves and may determine to increase the reserves at any time in the future if, based upon the factors set forth, it believes it would be appropriate to do so. Environmental Matters As previously disclosed, Merck’s facilities in Oss, the Netherlands, were inspected in 2012 by the Province of Brabant (Province) pursuant to the Dutch Hazards of Major Accidents Decree and the sites’ environmental permits. The Province issued penalties for alleged violations of regulations governing preventing and managing accidents with hazardous substances, and the government also issued a fine for alleged environmental violations at one of the Oss facilities, which together totaled $235 thousand . The Company was subsequently advised that a criminal investigation had been initiated based upon certain of the issues that formed the basis of the administrative enforcement action by the Province. As previously disclosed, the matter was settled, without any admission of liability, for an aggregate payment of €400 thousand . The Company and its subsidiaries are parties to a number of proceedings brought under the Comprehensive Environmental Response, Compensation and Liability Act, commonly known as Superfund, and other federal and state equivalents. These proceedings seek to require the operators of hazardous waste disposal facilities, transporters of waste to the sites and generators of hazardous waste disposed of at the sites to clean up the sites or to reimburse the government for cleanup costs. The Company has been made a party to these proceedings as an alleged generator of waste disposed of at the sites. In each case, the government alleges that the defendants are jointly and severally liable for the cleanup costs. Although joint and several liabili

Equity

Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Equity	Equity The Merck certificate of incorporation authorizes 6,500,000,000 shares of common stock and 20,000,000 shares of preferred stock. Capital Stock A summary of common stock and treasury stock transactions (shares in millions) is as follows: 2018 2017 2016 Common Stock Treasury Stock Common Stock Treasury Stock Common Stock Treasury Stock Balance January 1 3,577 880 3,577 828 3,577 796 Purchases of treasury stock — 122 — 67 — 60 Issuances (1) — (17 ) — (15 ) — (28 ) Balance December 31 3,577 985 3,577 880 3,577 828 (1) Issuances primarily reflect activity under share-based compensation plans. On October 25, 2018, the Company entered into accelerated share repurchase (ASR) agreements with two third-party financial institutions (Dealers). Under the ASR agreements, Merck agreed to purchase $5 billion of Merck’s common stock, in total, with an initial delivery of 56.7 million shares of Merck’s common stock, based on the then-current market price, made by the Dealers to Merck, and payments of $5 billion made by Merck to the Dealers on October 29, 2018, which were funded with existing cash and investments, as well as short-term borrowings. The payments to the Dealers were recorded as reductions to shareholders’ equity, consisting of a $4 billion increase in treasury stock, which reflects the value of the initial 56.7 million shares received on October 29, 2018, and a $1 billion decrease in other-paid-in capital, which reflects the value of the stock held back by the Dealers pending final settlement. The number of shares of Merck’s common stock that Merck may receive, or may be required to remit, upon final settlement under the ASR agreements will be based upon the average daily volume weighted-average price of Merck’s common stock during the term of the ASR program, less a negotiated discount. Final settlement of the transaction under the ASR agreements is expected to occur in the first half of 2019, but may occur earlier at the option of the Dealers, or later under certain circumstances. If Merck is obligated to make adjustment payments to the Dealers under the ASR agreements, Merck may elect to satisfy such obligations in cash or in shares of Merck’s common stock.

Share-Based Compensation Plans

Share-Based Compensation Plans	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation Plans	Share-Based Compensation Plans The Company has share-based compensation plans under which the Company grants restricted stock units (RSUs) and performance share units (PSUs) to certain management level employees. In addition, employees and non-employee directors may be granted options to purchase shares of Company common stock at the fair market value at the time of grant. These plans were approved by the Company’s shareholders. At December 31, 2018 , 111 million shares collectively were authorized for future grants under the Company’s share-based compensation plans. These awards are settled primarily with treasury shares. Employee stock options are granted to purchase shares of Company stock at the fair market value at the time of grant. These awards generally vest one-third each year over a three -year period, with a contractual term of 7 - 10 years. RSUs are stock awards that are granted to employees and entitle the holder to shares of common stock as the awards vest. The fair value of the stock option and RSU awards is determined and fixed on the grant date based on the Company’s stock price. PSUs are stock awards where the ultimate number of shares issued will be contingent on the Company’s performance against a pre-set objective or set of objectives. The fair value of each PSU is determined on the date of grant based on the Company’s stock price. For RSUs and PSUs, dividends declared during the vesting period are payable to the employees only upon vesting. Over the PSU performance period, the number of shares of stock that are expected to be issued will be adjusted based on the probability of achievement of a performance target and final compensation expense will be recognized based on the ultimate number of shares issued. RSU and PSU distributions will be in shares of Company stock after the end of the vesting or performance period, subject to the terms applicable to such awards. PSU awards generally vest after three years. Prior to 2018, RSU awards generally vested after three years; beginning with awards granted in 2018, RSU awards generally vest one-third each year over a three -year period. Total pretax share-based compensation cost recorded in 2018 , 2017 and 2016 was $348 million , $312 million and $300 million , respectively, with related income tax benefits of $55 million , $57 million and $92 million , respectively. The Company uses the Black-Scholes option pricing model for determining the fair value of option grants. In applying this model, the Company uses both historical data and current market data to estimate the fair value of its options. The Black-Scholes model requires several assumptions including expected dividend yield, risk-free interest rate, volatility, and term of the options. The expected dividend yield is based on historical patterns of dividend payments. The risk-free rate is based on the rate at grant date of zero-coupon U.S. Treasury Notes with a term equal to the expected term of the option. Expected volatility is estimated using a blend of historical and implied volatility. The historical component is based on historical monthly price changes. The implied volatility is obtained from market data on the Company’s traded options. The expected life represents the amount of time that options granted are expected to be outstanding, based on historical and forecasted exercise behavior. The weighted average exercise price of options granted in 2018 , 2017 and 2016 was $58.15 , $63.88 and $54.63 per option, respectively. The weighted average fair value of options granted in 2018 , 2017 and 2016 was $8.26 , $7.04 and $5.89 per option, respectively, and were determined using the following assumptions: Years Ended December 31 2018 2017 2016 Expected dividend yield 3.4 % 3.6 % 3.8 % Risk-free interest rate 2.9 % 2.0 % 1.4 % Expected volatility 19.1 % 17.8 % 19.6 % Expected life (years) 6.1 6.1 6.2 Summarized information relative to stock option plan activity (options in thousands) is as follows: Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding January 1, 2018 36,274 $ 46.77 Granted 3,520 58.15 Exercised (14,598 ) 40.51 Forfeited (1,389 ) 53.80 Outstanding December 31, 2018 23,807 $ 51.89 5.95 $ 584 Exercisable December 31, 2018 16,184 $ 48.85 4.82 $ 446 Additional information pertaining to stock option plans is provided in the table below: Years Ended December 31 2018 2017 2016 Total intrinsic value of stock options exercised $ 348 $ 236 $ 444 Fair value of stock options vested 29 30 28 Cash received from the exercise of stock options 591 499 939 A summary of nonvested RSU and PSU activity (shares in thousands) is as follows: RSUs PSUs Number of Shares Weighted Average Grant Date Fair Value Number of Shares Weighted Average Grant Date Fair Value Nonvested January 1, 2018 13,609 $ 59.32 1,868 $ 60.03 Granted 7,270 58.46 1,081 57.17 Vested (3,766 ) 59.66 (758 ) 57.59 Forfeited (985 ) 59.30 (152 ) 60.06 Nonvested December 31, 2018 16,128 $ 58.85 2,039 $ 59.42 At December 31, 2018 , there was $560 million of total pretax unrecognized compensation expense related to nonvested stock options, RSU and PSU awards which will be recognized over a weighted average period of 1.9 years. For segment reporting, share-based compensation costs are unallocated expenses.

Pension and Other Postretiremen

Pension and Other Postretirement Benefit Plans	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefit Plans	Pension and Other Postretirement Benefit Plans The Company has defined benefit pension plans covering eligible employees in the United States and in certain of its international subsidiaries. In addition, the Company provides medical benefits, principally to its eligible U.S. retirees and their dependents, through its other postretirement benefit plans. The Company uses December 31 as the year-end measurement date for all of its pension plans and other postretirement benefit plans. Net Periodic Benefit Cost The net periodic benefit cost (credit) for pension and other postretirement benefit plans consisted of the following components: Pension Benefits U.S. International Other Postretirement Benefits Years Ended December 31 2018 2017 2016 2018 2017 2016 2018 2017 2016 Service cost $ 326 $ 312 $ 282 $ 238 $ 252 $ 238 $ 57 $ 57 $ 54 Interest cost 432 454 456 178 172 204 69 81 82 Expected return on plan assets (851 ) (862 ) (831 ) (431 ) (393 ) (382 ) (83 ) (78 ) (107 ) Amortization of unrecognized prior service cost (50 ) (53 ) (55 ) (13 ) (11 ) (11 ) (84 ) (98 ) (106 ) Net loss amortization 232 180 119 84 98 87 1 1 3 Termination benefits 19 44 23 2 4 4 3 8 4 Curtailments 10 3 5 1 (4 ) (1 ) (8 ) (31 ) (18 ) Settlements 5 — — 13 5 6 — — — Net periodic benefit cost (credit) $ 123 $ 78 $ (1 ) $ 72 $ 123 $ 145 $ (45 ) $ (60 ) $ (88 ) The changes in net periodic benefit cost (credit) year over year for pension plans are largely attributable to changes in the discount rate affecting net loss amortization. In connection with restructuring actions (see Note 5), termination charges were recorded in 2018 , 2017 and 2016 on pension and other postretirement benefit plans related to expanded eligibility for certain employees exiting Merck. Also, in connection with these restructuring activities, curtailments were recorded on pension and other postretirement benefit plans and settlements were recorded on certain U.S. and international pension plans as reflected in the table above. The components of net periodic benefit cost (credit) other than the service cost component are included in Other (income) expense, net (see Note 15), with the exception of certain amounts for termination benefits, curtailments and settlements, which are recorded in Restructuring costs if the event giving rise to the termination benefits, curtailment or settlement is related to restructuring actions as noted above. Obligations and Funded Status Summarized information about the changes in plan assets and benefit obligations, the funded status and the amounts recorded at December 31 is as follows: Pension Benefits Other Postretirement Benefits U.S. International 2018 2017 2018 2017 2018 2017 Fair value of plan assets January 1 $ 10,896 $ 9,766 $ 9,339 $ 7,794 $ 1,114 $ 1,019 Actual return on plan assets (810 ) 1,723 (289 ) 677 (72 ) 161 Company contributions, net 378 58 167 226 6 (4 ) Effects of exchange rate changes — — (352 ) 843 — — Benefits paid (772 ) (651 ) (202 ) (198 ) (80 ) (62 ) Settlements (44 ) — (106 ) (17 ) — — Other — — 23 14 — — Fair value of plan assets December 31 $ 9,648 $ 10,896 $ 8,580 $ 9,339 $ 968 $ 1,114 Benefit obligation January 1 $ 11,904 $ 10,849 $ 9,483 $ 8,372 $ 1,922 $ 1,922 Service cost 326 312 238 252 57 57 Interest cost 432 454 178 172 69 81 Actuarial (gains) losses (1) (1,258 ) 881 (154 ) (7 ) (341 ) (87 ) Benefits paid (772 ) (651 ) (202 ) (198 ) (80 ) (62 ) Effects of exchange rate changes — — (387 ) 916 (6 ) 3 Plan amendments — — 10 (22 ) (9 ) — Curtailments 13 15 (2 ) (3 ) — — Termination benefits 19 44 2 4 3 8 Settlements (44 ) — (106 ) (17 ) — — Other — — 23 14 — — Benefit obligation December 31 $ 10,620 $ 11,904 $ 9,083 $ 9,483 $ 1,615 $ 1,922 Funded status December 31 $ (972 ) $ (1,008 ) $ (503 ) $ (144 ) $ (647 ) $ (808 ) Recognized as: Other assets $ — $ — $ 659 $ 828 $ — $ — Accrued and other current liabilities (47 ) (59 ) (14 ) (17 ) (10 ) (11 ) Other noncurrent liabilities (925 ) (949 ) (1,148 ) (955 ) (637 ) (797 ) (1) Actuarial (gains) losses in 2018 and 2017 primarily reflect changes in discount rates. At December 31, 2018 and 2017 , the accumulated benefit obligation was $19.0 billion and $20.5 billion , respectively, for all pension plans, of which $10.4 billion and $11.5 billion , respectively, related to U.S. pension plans. Information related to the funded status of selected pension plans at December 31 is as follows: U.S. International 2018 2017 2018 2017 Pension plans with a projected benefit obligation in excess of plan assets Projected benefit obligation $ 10,620 $ 11,904 $ 6,251 $ 3,323 Fair value of plan assets 9,648 10,896 5,089 2,352 Pension plans with an accumulated benefit obligation in excess of plan assets Accumulated benefit obligation $ 9,702 $ 676 $ 5,936 $ 2,120 Fair value of plan assets 8,966 — 5,071 1,346 Plan Assets Entities are required to use a fair value hierarchy which maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. There are three levels of inputs used to measure fair value with Level 1 having the highest priority and Level 3 having the lowest: Level 1 — Quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity. The Level 3 assets are those whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques with significant unobservable inputs, as well as instruments for which the determination of fair value requires significant judgment or estimation. At December 31, 2018 and 2017 , $826 million and $488 million , respectively, or approximately 5% and 2% , respectively, of the Company’s pension investments were categorized as Level 3 assets. If the inputs used to measure the financial assets fall within more than one level described above, the categorization is based on the lowest level input that is significant to the fair value measurement of the instrument. The fair values of the Company’s pension plan assets at December 31 by asset category are as follows: Fair Value Measurements Using Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total 2018 2017 U.S. Pension Plans Assets Cash and cash equivalents $ 40 $ — $ — $ 40 $ 6 $ — $ — $ 6 Investment funds Developed markets equities 169 — — 169 390 — — 390 Emerging markets equities 121 — — 121 138 — — 138 Equity securities Developed markets 2,172 — — 2,172 2,743 — — 2,743 Fixed income securities Government and agency obligations — 1,509 — 1,509 — 757 — 757 Corporate obligations — 1,246 — 1,246 — 900 — 900 Mortgage and asset-backed securities — 262 — 262 — 240 — 240 Other investments — — 13 13 — — 15 15 Net assets in fair value hierarchy $ 2,502 $ 3,017 $ 13 $ 5,532 $ 3,277 $ 1,897 $ 15 $ 5,189 Investments measured at NAV (1) 4,116 5,707 Plan assets at fair value $ 9,648 $ 10,896 International Pension Plans Assets Cash and cash equivalents $ 50 $ 3 $ — $ 53 $ 54 $ 19 $ — $ 73 Investment funds Developed markets equities 461 3,071 — 3,532 562 3,326 — 3,888 Emerging markets equities 56 112 — 168 62 176 — 238 Government and agency obligations 372 2,082 — 2,454 249 2,095 — 2,344 Corporate obligations 4 7 — 11 5 329 — 334 Fixed income obligations 7 4 — 11 7 4 — 11 Real estate (2) — 1 1 2 — 1 2 3 Equity securities Developed markets 544 — — 544 660 — — 660 Fixed income securities Government and agency obligations 2 291 — 293 2 266 — 268 Corporate obligations 1 113 — 114 1 118 — 119 Mortgage and asset-backed securities — 55 — 55 — 55 — 55 Other investments Insurance contracts (3) — 66 811 877 — 67 470 537 Other — 4 1 5 — 6 1 7 Net assets in fair value hierarchy $ 1,497 $ 5,809 $ 813 $ 8,119 $ 1,602 $ 6,462 $ 473 $ 8,537 Investments measured at NAV (1) 461 802 Plan assets at fair value $ 8,580 $ 9,339 (1) Certain investments that were measured at net asset value (NAV) per share or its equivalent as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the fair value of plan assets at December 31, 2018 and 2017 . (2) The plans’ Level 3 investments in real estate funds are generally valued by market appraisals of the underlying investments in the funds. (3) The plans’ Level 3 investments in insurance contracts are generally valued using a crediting rate that approximates market returns and invest in underlying securities whose market values are unobservable and determined using pricing models, discounted cash flow methodologies, or similar techniques. The table below provides a summary of the changes in fair value, including transfers in and/or out, of all financial assets measured at fair value using significant unobservable inputs (Level 3) for the Company’s pension plan assets: 2018 2017 Insurance Contracts Real Estate Other Total Insurance Contracts Real Estate Other Total U.S. Pension Plans Balance January 1 $ — $ — $ 15 $ 15 $ — $ — $ 18 $ 18 Actual return on plan assets: Relating to assets still held at December 31 — — (3 ) (3 ) — — (2 ) (2 ) Relating to assets sold during the year — — 4 4 — — 4 4 Purchases and sales, net — — (3 ) (3 ) — — (5 ) (5 ) Balance December 31 $ — $ — $ 13 $ 13 $ — $ — $ 15 $ 15 International Pension Plans Balance January 1 $ 470 $ 2 $ 1 $ 473 $ 412 $ 4 $ 1 $ 417 Actual return on plan assets: Relating to assets still held at December 31 (32 ) — — (32 ) 52 — — 52 Purchases and sales, net 380 (1 ) — 379 5 (2 ) — 3 Transfers into Level 3 (7 ) — — (7 ) 1 — — 1 Balance December 31 $ 811 $ 1 $ 1 $ 813 $ 470 $ 2 $ 1 $ 473 The fair values of the Company’s other postretirement benefit plan assets at December 31 by asset category are as follows: Fair Value Measurements Using Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total 2018 2017 Assets Cash and cash equivalents $ 78 $ — $ — $ 78 $ 97 $ — $ — $ 97 Investment funds Developed markets equities 16 — — 16 37 — — 37 Emerging markets equities 12 — — 12 13 — — 13 Government and agency obligations 1 — — 1 1 — — 1 Equity securities Developed markets 200 — — 200 256 — — 256 Fixed income securities Government and agency obligations — 141 — 141 — 71 — 71 Corporate obligations — 116 — 116 — 84 — 84 Mortgage and asset-backed securities — 24 — 24 — 23 — 23 Net assets in fair value hierarchy $ 307 $ 281 $ — $ 588 $ 404 $ 178 $ — $ 582 Investments measured at NAV (1) 380 532 Plan assets at fair value $ 968 $ 1,114 (1) Certain investments that were measured at net asset value (NAV) per share or its equivalent as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the fair value of plan assets at December 31, 2018 and 2017 . The Company has established investment guidelines for its U.S. pension and other postretirement plans to create an asset allocation that is expected to deliver a rate of return sufficient to meet the long-term obligation of each plan, given an acceptable level of risk. The target investment portfolio of the Company’s U.S. pension and other postretirement benefit plans is allocated 30% to 50% in U.S. equities, 15% to 30% in international equities, 30% to 45% in fixed-income investments, and up to 5% in cash and other investments. The portfolio’s equity weighting is consistent with the long-term nature of the plans’ benefit obligations. The expected annual standard deviation of returns of the target portfolio, which approximates 11% , reflects both the equity allocation and the diversification benefits among the asset classes in which the portfolio invests. For international pension plans, the targeted investment portfolio varies based on the duration of pension liabilities and local government rules and regulations. Although a significant percentage of plan assets are invested in U.S. equities, concentration risk is mitigated through the use of strategies that are diversified within management guidelines. Expected Contributions Expected contributions during 2019 are approximately $50 million for U.S. pension plans, approximately $150 million for international pension plans and approximately $15 million for other postretirement benefit plans. Expected Benefit Payments Expected benefit payments are as follows: U.S. Pension Benefits International Pension Benefits Other Postretirement Benefits 2019 $ 638 $ 225 $ 91 2020 661 213 95 2021 680 221 98 2022 685 239 102 2023 709 249 105 2024 — 2028 3,805 1,349 577 Expected benefit payments are based on the same assumptions used to measure the benefit obligations and include estimated future employee service. Amounts Recognized in Other Comprehensive Income Net loss amounts reflect experience differentials primarily relating to differences between expected and actual returns on plan assets as well as the effects of changes in actuarial assumptions. Net loss amounts in excess of certain thresholds are amortized into net periodic benefit cost over the average remaining service life of employees. The following amounts were reflected as components of OCI : Pension Plans Other Postretirement Benefit Plans U.S. International Years Ended December 31 2018 2017 2016 2018 2017 2016 2018 2017 2016 Net (loss) gain arising during the period $ (397 ) $ (19 ) $ (743 ) $ (505 ) $ 309 $ (380 ) $ 186 $ 170 $ (45 ) Prior service (cost) credit arising during the period (4 ) (13 ) (10 ) (10 ) 22 (2 ) 2 (31 ) (19 ) $ (401 ) $ (32 ) $ (753 ) $ (515 ) $ 331 $ (382 ) $ 188 $ 139 $ (64 ) Net loss amortization included in benefit cost $ 232 $ 180 $ 119 $ 84 $ 98 $ 87 $ 1 $ 1 $ 3 Prior service (credit) cost amortization included in benefit cost (50 ) (53 ) (55 ) (13 ) (11 ) (11 ) (84 ) (98 ) (106 ) $ 182 $ 127 $ 64 $ 71 $ 87 $ 76 $ (83 ) $ (97 ) $ (103 ) The estimated net loss (gain) and prior service cost (credit) amounts that will be amortized from AOCI into net periodic benefit cost during 2019 are $204 million and $(62) million , respectively, for pension plans (of which $141 million and $(50) million , respectively, relates to U.S. pension plans) and $(7) million and $(78) million , respectively, for other postretirement benefit plans. Actuarial Assumptions The Company reassesses its benefit plan assumptions on a regular basis. The weighted average assumptions used in determining U.S. pension and other postretirement benefit plan and international pension plan information are as follows: U.S. Pension and Other Postretirement Benefit Plans International Pension Plans December 31 2018 2017 2016 2018 2017 2016 Net periodic benefit cost Discount rate 3.70 % 4.30 % 4.70 % 2.10 % 2.20 % 2.80 % Expected rate of return on plan assets 8.20 % 8.70 % 8.60 % 5.10 % 5.10 % 5.60 % Salary growth rate 4.30 % 4.30 % 4.30 % 2.90 % 2.90 % 2.90 % Benefit obligation Discount rate 4.40 % 3.70 % 4.30 % 2.20 % 2.10 % 2.20 % Salary growth rate 4.30 % 4.30 % 4.30 % 2.80 % 2.90 % 2.90 % For both the pension and other postretirement benefit plans, the discount rate is evaluated on measurement dates and modified to reflect the prevailing market rate of a portfolio of high-quality fixed-income debt instruments that would provide the future cash flows needed to pay the benefits included in the benefit obligation as they come due. The expected rate of return for both the pension and other postretirement benefit plans represents the average rate of return to be earned on plan assets over the period the benefits included in the benefit obligation are to be paid and is determined on a plan basis. The expected rate of return within each plan is developed considering long-term historical returns data, current market conditions, and actual returns on the plan assets. Using this reference information, the long-term return expectations for each asset category and a weighted average expected return for each plan’s target portfolio is developed, according to the allocation among those investment categories. The expected portfolio performance reflects the contribution of active management as appropriate. For 2019 , the expected rate of return for the Company’s U.S. pension and other postretirement benefit plans will range from 7.70% to 8.10% , as compared to a range of 7.70% to 8.30% in 2018 . The decrease is primarily due to a modest shift in asset allocation. The change in the weighted-average expected return on U.S. pension and other postretirement benefit plan assets from 2016 to 2018 is due to the relative weighting of the referenced plans’ assets. The health care cost trend rate assumptions for other postretirement benefit plans are as follows: December 31 2018 2017 Health care cost trend rate assumed for next year 7.0 % 7.2 % Rate to which the cost trend rate is assumed to decline 4.5 % 4.5 % Year that the trend rate reaches the ultimate trend rate 2032 2032 A one percentage point change in the health care cost trend rate would have had the following effects: One Percentage Point Increase Decrease Effect on total service and interest cost components $ 11 $ (9 ) Effect on benefit obligation 88 (74 ) Savings Plans The Company also maintains defined contribution savings plans in the United States. The Company matches a percentage of each employee’s contributions consistent with the provisions of the plan for which the employee is eligible. Total employer contributions to these plans in 2018 , 2017 and 2016 were $136 million , $131 million and $126 million , respectively.

Other (Income) Expense, Net

Other (Income) Expense, Net	12 Months Ended
	Dec. 31, 2018
Other Income and Expenses [Abstract]
Other (Income) Expense, Net	Other (Income) Expense, Net Other (income) expense, net, consisted of: Years Ended December 31 2018 2017 2016 Interest income $ (343 ) $ (385 ) $ (328 ) Interest expense 772 754 693 Exchange losses (gains) 145 (11 ) 174 Income on investments in equity securities, net (1) (324 ) (352 ) (43 ) Net periodic defined benefit plan (credit) cost other than service cost (512 ) (512 ) (531 ) Other, net (140 ) 6 224 $ (402 ) $ (500 ) $ 189 (1) Includes net realized and unrealized gains and losses on investments in equity securities either owned directly or through ownership interests in investment funds. Income on investments in equity securities, net, in 2018 reflects the recognition of unrealized net gains pursuant to the prospective adoption of ASU 2016-01 on January 1, 2018 (see Note 2). The increase in income on investments in equity securities, net, in 2017 was driven primarily by higher realized gains on sales. Other, net (as presented in the table above) in 2018 includes a gain of $115 million related to the settlement of certain patent litigation (see Note 11), income of $99 million related to AstraZeneca’s option exercise (see Note 9), and a gain of $85 million resulting from the receipt of a milestone payment for an out-licensed migraine clinical development program. Other, net in 2018 also includes $144 million of goodwill impairment charges related to certain businesses in the Healthcare Services segment (see Note 8), as well as $41 million of charges related to the write-down of assets held for sale to fair value in anticipation of the dissolution of the Company’s joint venture with Supera Farma Laboratorios S.A. in Brazil. Other, net in 2017 includes income of $232 million related to AstraZeneca’s option exercise and a $191 million loss on extinguishment of debt (see Note 10). Other, net in 2016 includes a charge of $625 million related to the previously disclosed settlement of worldwide patent litigation related to Keytruda , a gain of $117 million related to the settlement of other patent litigation, gains of $100 million resulting from the receipt of milestone payments for out-licensed migraine clinical development programs, and $98 million of income related to AstraZeneca’s option exercise. Interest paid was $777 million in 2018 , $723 million in 2017 and $686 million in 2016 .

Taxes on Income

Taxes on Income	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Taxes on Income	Taxes on Income A reconciliation between the effective tax rate and the U.S. statutory rate is as follows: 2018 2017 2016 Amount Tax Rate Amount Tax Rate Amount Tax Rate U.S. statutory rate applied to income before taxes $ 1,827 21.0 % $ 2,282 35.0 % $ 1,631 35.0 % Differential arising from: Impact of the TCJA 289 3.3 2,625 40.3 — — Valuation allowances 269 3.1 632 9.7 (5 ) (0.1 ) Impact of purchase accounting adjustments, including amortization 267 3.1 713 10.9 623 13.4 State taxes 201 2.3 77 1.2 173 3.7 Restructuring 56 0.6 142 2.2 145 3.1 Foreign earnings (245 ) (2.8 ) (1,654 ) (25.4 ) (1,546 ) (33.2 ) R&D tax credit (96 ) (1.1 ) (71 ) (1.1 ) (58 ) (1.3 ) Tax settlements (22 ) (0.3 ) (356 ) (5.5 ) — — Other (1) (38 ) (0.4 ) (287 ) (4.4 ) (245 ) (5.2 ) $ 2,508 28.8 % $ 4,103 62.9 % $ 718 15.4 % (1) Other includes the tax effects of losses on foreign subsidiaries and miscellaneous items. The Company’s 2017 effective tax rate reflected a provisional impact of 40.3% for the Tax Cuts and Jobs Act (TCJA), which was enacted on December 22, 2017. Among other provisions, the TCJA reduced the U.S. federal corporate statutory tax rate from 35% to 21% effective January 1, 2018, requires companies to pay a one-time transition tax on undistributed earnings of certain foreign subsidiaries, and creates new taxes on certain foreign sourced earnings. The Company reflected the impact of the TCJA in its 2017 financial statements. However, since application of certain provisions of the TCJA remained subject to further interpretation, in certain instances the Company made reasonable estimates of the effects of the TCJA. In 2018, these amounts were finalized as described below. The one-time transition tax is based on the Company’s post-1986 undistributed earnings and profits (E&P). For a substantial portion of these undistributed E&P, the Company had not previously provided deferred taxes as these earnings were deemed by Merck to be retained indefinitely by subsidiary companies for reinvestment. The Company recorded a provisional amount in 2017 for its one-time transition tax liability of $5.3 billion . This provisional amount was reduced by the reversal of $2.0 billion of deferred taxes that were previously recorded in connection with the merger of Schering-Plough Corporation in 2009 for certain undistributed foreign E&P. On the basis of revised calculations of post-1986 undistributed foreign E&P and finalization of the amounts held in cash or other specified assets, the Company recognized a measurement-period adjustment of $124 million in 2018 related to the transition tax obligation, with a corresponding adjustment to income tax expense during the period, resulting in a revised transition tax obligation of $5.5 billion . The Company anticipates that it will be able to utilize certain foreign tax credits to partially reduce the transition tax payment. As permitted under the TCJA, the Company has elected to pay the one-time transition tax over a period of eight years. After payment of the amount due in 2018, the remaining transition tax liability at December 31, 2018, is $4.9 billion , of which $275 million is included in Income Taxes Payable and the remainder of $4.6 billion is included in Other Noncurrent Liabilities . As a result of the TCJA, the Company has made a determination it is no longer indefinitely reinvested with respect to its undistributed earnings from foreign subsidiaries and has provided a deferred tax liability for withholding tax that would apply. In 2017, the Company remeasured its deferred tax assets and liabilities at the new federal statutory tax rate of 21%, which resulted in a provisional deferred tax benefit of $779 million . On the basis of clarifications to the deferred tax benefit calculation, the Company recorded measurement-period adjustments in 2018 of $32 million related to deferred income taxes. Beginning in 2018, the TCJA includes a tax on “global intangible low-taxed income” (GILTI) as defined in the TCJA. The Company has made an accounting policy election to account for the tax effects of the GILTI tax in the income tax provision in future periods as the tax arises. The foreign earnings tax rate differentials in the tax rate reconciliation above primarily reflect the impacts of operations in jurisdictions with different tax rates than the United States, particularly Ireland and Switzerland, as well as Singapore and Puerto Rico which operate under tax incentive grants (which begin to expire in 2022), where the earnings had been indefinitely reinvested, thereby yielding a favorable impact on the effective tax rate compared with the U.S. statutory rate of 35% in 2017 and 2016 and 21% in 2018. The foreign earnings tax rate differentials do not include the impact of intangible asset impairment charges, amortization of purchase accounting adjustments or restructuring costs. These items are presented separately as they each represent a significant, separately disclosed pretax cost or charge, and a substantial portion of each of these items relates to jurisdictions with lower tax rates than the United States. Therefore, the impact of recording these expense items in lower tax rate jurisdictions is an unfavorable impact on the effective tax rate compared to the U.S. statutory rate of 35% in 2017 and 2016 and 21% in 2018. Income before taxes consisted of: Years Ended December 31 2018 2017 2016 Domestic $ 3,717 $ 3,483 $ 518 Foreign 4,984 3,038 4,141 $ 8,701 $ 6,521 $ 4,659 Taxes on income consisted of: Years Ended December 31 2018 2017 2016 Current provision Federal $ 536 $ 5,585 $ 1,166 Foreign 2,281 1,229 916 State 200 (90 ) 157 3,017 6,724 2,239 Deferred provision Federal (402 ) (2,958 ) (1,255 ) Foreign (64 ) 75 (225 ) State (43 ) 262 (41 ) (509 ) (2,621 ) (1,521 ) $ 2,508 $ 4,103 $ 718 Deferred income taxes at December 31 consisted of: 2018 2017 Assets Liabilities Assets Liabilities Product intangibles and licenses $ 720 $ 1,640 $ 307 $ 2,256 Inventory related 32 377 29 499 Accelerated depreciation — 582 28 642 Pensions and other postretirement benefits 565 151 498 192 Compensation related 291 — 314 — Unrecognized tax benefits 174 — 156 — Net operating losses and other tax credit carryforwards 715 — 654 — Other 621 66 909 52 Subtotal 3,118 2,816 2,895 3,641 Valuation allowance (1,348 ) (900 ) Total deferred taxes $ 1,770 $ 2,816 $ 1,995 $ 3,641 Net deferred income taxes $ 1,046 $ 1,646 Recognized as: Other assets $ 656 $ 573 Deferred income taxes $ 1,702 $ 2,219 The Company has net operating loss (NOL) carryforwards in several jurisdictions. As of December 31, 2018 , $715 million of deferred taxes on NOL carryforwards relate to foreign jurisdictions. Valuation allowances of $1.3 billion have been established on these foreign NOL carryforwards and other foreign deferred tax assets. The Company has no NOL carryforwards relating to U.S. jurisdictions. Income taxes paid in 2018 , 2017 and 2016 were $1.5 billion , $4.9 billion and $1.8 billion , respectively. Tax benefits relating to stock option exercises were $77 million in 2018 , $73 million in 2017 and $147 million in 2016 . A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: 2018 2017 2016 Balance January 1 $ 1,723 $ 3,494 $ 3,448 Additions related to current year positions 221 146 196 Additions related to prior year positions 142 520 75 Reductions for tax positions of prior years (1) (73 ) (1,038 ) (90 ) Settlements (1) (91 ) (1,388 ) (92 ) Lapse of statute of limitations (29 ) (11 ) (43 ) Balance December 31 $ 1,893 $ 1,723 $ 3,494 (1) Amounts reflect the settlements with the IRS as discussed below. If the Company were to recognize the unrecognized tax benefits of $1.9 billion at December 31, 2018 , the income tax provision would reflect a favorable net impact of $1.8 billion . The Company is under examination by numerous tax authorities in various jurisdictions globally. The Company believes that it is reasonably possible that the total amount of unrecognized tax benefits as of December 31, 2018 could decrease by up to approximately $750 million in the next 12 months as a result of various audit closures, settlements or the expiration of the statute of limitations. The ultimate finalization of the Company’s examinations with relevant taxing authorities can include formal administrative and legal proceedings, which could have a significant impact on the timing of the reversal of unrecognized tax benefits. The Company believes that its reserves for uncertain tax positions are adequate to cover existing risks or exposures. Expenses for interest and penalties associated with uncertain tax positions amounted to $51 million in 2018 , $183 million in 2017 and $134 million in 2016 . These amounts reflect the beneficial impacts of various tax settlements, including those discussed below. Liabilities for accrued interest and penalties were $372 million and $341 million as of December 31, 2018 and 2017 , respectively. In 2017, the Internal Revenue Service (IRS) concluded its examinations of Merck’s 2006-2011 U.S. federal income tax returns. As a result, the Company was required to make a payment of approximately $2.8 billion . The Company’s reserves for unrecognized tax benefits for the years under examination exceeded the adjustments relating to this examination period and therefore the Company recorded a net $234 million tax benefit in 2017. This net benefit reflects reductions in reserves for unrecognized tax benefits for tax positions relating to the years that were under examination, partially offset by additional reserves for tax positions not previously reserved for, as well as adjustments to reserves for unrecognized tax benefits relating to years which remain open to examination that are affected by this settlement. The IRS is currently conducting examinations of the Company’s tax returns for the years 2012 through 2014. In addition, various state and foreign tax examinations are in progress and for these jurisdictions, the Company’s income tax returns are open for examination for the period 2003 through 2018.

Earnings per Share

Earnings per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings per Share	Earnings per Share The calculations of earnings per share (shares in millions) are as follows: Years Ended December 31 2018 2017 2016 Net income attributable to Merck & Co., Inc. $ 6,220 $ 2,394 $ 3,920 Average common shares outstanding 2,664 2,730 2,766 Common shares issuable (1) 15 18 21 Average common shares outstanding assuming dilution 2,679 2,748 2,787 Basic earnings per common share attributable to Merck & Co., Inc. common shareholders $ 2.34 $ 0.88 $ 1.42 Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders $ 2.32 $ 0.87 $ 1.41 (1) Issuable primarily under share-based compensation plans. In 2018 , 2017 and 2016 , 6 million , 5 million and 13 million , respectively, of common shares issuable under share-based compensation plans were excluded from the computation of earnings per common share assuming dilution because the effect would have been antidilutive.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2018
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Changes in AOCI by component are as follows: Derivatives Investments Employee Benefit Plans Cumulative Translation Adjustment Accumulated Other Comprehensive Income (Loss) Balance January 1, 2016, net of taxes $ 404 $ 41 $ (2,407 ) $ (2,186 ) $ (4,148 ) Other comprehensive income (loss) before reclassification adjustments, pretax 210 (38 ) (1,199 ) (150 ) (1,177 ) Tax (72 ) 16 363 (19 ) 288 Other comprehensive income (loss) before reclassification adjustments, net of taxes 138 (22 ) (836 ) (169 ) (889 ) Reclassification adjustments, pretax (314 ) (1) (31 ) (2) 37 (3) — (308 ) Tax 110 9 — — 119 Reclassification adjustments, net of taxes (204 ) (22 ) 37 — (189 ) Other comprehensive income (loss), net of taxes (66 ) (44 ) (799 ) (169 ) (1,078 ) Balance December 31, 2016, net of taxes 338 (3 ) (3,206 ) (2,355 ) (5,226 ) Other comprehensive income (loss) before reclassification adjustments, pretax (561 ) 212 438 235 324 Tax 207 (35 ) (106 ) 166 232 Other comprehensive income (loss) before reclassification adjustments, net of taxes (354 ) 177 332 401 556 Reclassification adjustments, pretax (141 ) (1) (291 ) (2) 117 (3) — (315 ) Tax 49 56 (30 ) — 75 Reclassification adjustments, net of taxes (92 ) (235 ) 87 — (240 ) Other comprehensive income (loss), net of taxes (446 ) (58 ) 419 401 316 Balance December 31, 2017, net of taxes (108 ) (61 ) (2,787 ) (4) (1,954 ) (4,910 ) Other comprehensive income (loss) before reclassification adjustments, pretax 228 (108 ) (728 ) (84 ) (692 ) Tax (55 ) 1 169 (139 ) (24 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes 173 (107 ) (559 ) (223 ) (716 ) Reclassification adjustments, pretax 157 (1) 97 (2) 170 (3) — 424 Tax (33 ) — (36 ) — (69 ) Reclassification adjustments, net of taxes 124 97 134 — 355 Other comprehensive income (loss), net of taxes 297 (10 ) (425 ) (223 ) (361 ) Adoption of ASU 2018-02 (see Note 2) (23 ) 1 (344 ) 100 (266 ) Adoption of ASU 2016-01 (see Note 2) — (8 ) — — (8 ) Balance December 31, 2018, net of taxes $ 166 $ (78 ) $ (3,556 ) (4) $ (2,077 ) $ (5,545 ) (1) Relates to foreign currency cash flow hedges that were reclassified from AOCI to Sales . (2) Represents net realized (gains) losses on the sales of available-for-sale investments that were reclassified from AOCI to Other (income) expense, net . In 2017 and 2016, these amounts included both investments in debt and equity securities; however, as a result of the adoption of ASU 2016-01 (see Note 2), in 2018, these amounts relate only to investments in available-for-sale debt securities. (3) Includes net amortization of prior service cost and actuarial gains and losses included in net periodic benefit cost (see Note 14). (4) Includes pension plan net loss of $ 4.4 billion and $3.5 billion at December 31, 2018 and 2017 , respectively, and other postretirement benefit plan net (gain) loss of $(170) million and $(16) million at December 31, 2018 and 2017 , respectively, as well as pension plan prior service credit of $314 million and $326 million at December 31, 2018 and 2017 , respectively, and other postretirement benefit plan prior service credit of $375 million and $383 million at December 31, 2018 and 2017 , respectively.

Segment Reporting

Segment Reporting	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment Reporting	Segment Reporting The Company’s operations are principally managed on a products basis and include four operating segments, which are the Pharmaceutical, Animal Health, Healthcare Services and Alliances segments. The Pharmaceutical and Animal Health segments are the only reportable segments. The Animal Health segment met the criteria for separate reporting and became a reportable segment in 2018. The Pharmaceutical segment includes human health pharmaceutical and vaccine products. Human health pharmaceutical products consist of therapeutic and preventive agents, generally sold by prescription, for the treatment of human disorders. The Company sells these human health pharmaceutical products primarily to drug wholesalers and retailers, hospitals, government agencies and managed health care providers such as health maintenance organizations, pharmacy benefit managers and other institutions. Human health vaccine products consist of preventive pediatric, adolescent and adult vaccines, primarily administered at physician offices. The Company sells these human health vaccines primarily to physicians, wholesalers, physician distributors and government entities. A large component of pediatric and adolescent vaccine sales are made to the U.S. Centers for Disease Control and Prevention Vaccines for Children program, which is funded by the U.S. government. Additionally, the Company sells vaccines to the Federal government for placement into vaccine stockpiles. Sales of vaccines in most major European markets were marketed through the Company’s SPMSD joint venture until its termination on December 31, 2016 (see Note 9). The Animal Health segment discovers, develops, manufactures and markets animal health products, including pharmaceutical and vaccine products, for the prevention, treatment and control of disease in all major livestock and companion animal species, which the Company sells to veterinarians, distributors and animal producers. The Healthcare Services segment provides services and solutions that focus on engagement, health analytics and clinical services to improve the value of care delivered to patients. The Alliances segment primarily includes activity from the Company’s relationship with AstraZeneca LP related to sales of Nexium and Prilosec, which concluded in 2018 (see Note 9). Sales of the Company’s products were as follows: Years Ended December 31 2018 2017 2016 U.S. Int’l Total U.S. Int’l Total U.S. Int’l Total Pharmaceutical: Oncology Keytruda $ 4,150 $ 3,021 $ 7,171 $ 2,309 $ 1,500 $ 3,809 $ 792 $ 610 $ 1,402 Emend 312 210 522 342 213 556 356 193 549 Temodar 6 209 214 16 256 271 15 268 283 Alliance revenue - Lynparza 127 61 187 — 20 20 — — — Alliance revenue - Lenvima 95 54 149 — — — — — — Vaccines (1) Gardasil/Gardasil 9 1,873 1,279 3,151 1,565 743 2,308 1,780 393 2,173 ProQuad/M-M-R II/Varivax 1,430 368 1,798 1,374 303 1,676 1,362 279 1,640 Pneumovax 23 627 281 907 581 240 821 447 193 641 RotaTeq 496 232 728 481 204 686 482 169 652 Zostavax 22 195 217 422 246 668 518 168 685 Hospital Acute Care Bridion 386 531 917 239 465 704 77 405 482 Noxafil 353 389 742 309 327 636 284 312 595 Invanz 253 243 496 361 241 602 329 233 561 Cubicin 191 176 367 189 193 382 906 181 1,087 Cancidas 12 314 326 20 402 422 25 533 558 Primaxin 7 258 265 10 270 280 4 293 297 Immunology Simponi — 893 893 — 819 819 — 766 766 Remicade — 582 582 — 837 837 — 1,268 1,268 Neuroscience Belsomra 96 164 260 98 112 210 84 70 154 Virology Isentress/Isentress HD 513 627 1,140 565 639 1,204 721 666 1,387 Zepatier 8 447 455 771 888 1,660 488 67 555 Cardiovascular Zetia 45 813 857 352 992 1,344 1,588 972 2,560 Vytorin 10 487 497 124 627 751 473 668 1,141 Atozet — 347 347 — 225 225 1 146 146 Adempas — 329 329 — 300 300 — 169 169 Diabetes Januvia 1,969 1,718 3,686 2,153 1,584 3,737 2,286 1,622 3,908 Janumet 811 1,417 2,228 863 1,296 2,158 984 1,217 2,201 Women’s Health NuvaRing 722 180 902 564 197 761 576 202 777 Implanon/Nexplanon 495 208 703 496 191 686 420 186 606 Diversified Brands Singulair 20 688 708 40 692 732 40 874 915 Cozaar/Hyzaar 23 431 453 18 466 484 16 494 511 Nasonex 23 353 376 54 333 387 184 352 537 Arcoxia — 335 335 — 363 363 — 450 450 Follistim AQ 115 153 268 123 174 298 157 197 355 Dulera 186 28 214 261 26 287 412 24 436 Fosamax 4 205 209 6 235 241 5 279 284 Other pharmaceutical (2) 1,228 2,855 4,090 1,148 2,917 4,065 1,261 3,158 4,420 Total Pharmaceutical segment sales 16,608 21,081 37,689 15,854 19,536 35,390 17,073 18,077 35,151 Animal Health: Livestock 528 2,102 2,630 471 2,013 2,484 446 1,841 2,287 Companion Animals 710 872 1,582 619 772 1,391 543 648 1,191 Total Animal Health segment sales 1,238 2,974 4,212 1,090 2,785 3,875 989 2,489 3,478 Other segment sales (3) 248 2 250 396 1 397 385 — 385 Total segment sales 18,094 24,057 42,151 17,340 22,322 39,662 18,447 20,566 39,014 Other (4) 118 26 143 84 376 460 31 763 793 $ 18,212 $ 24,083 $ 42,294 $ 17,424 $ 22,698 $ 40,122 $ 18,478 $ 21,329 $ 39,807 U.S. plus international may not equal total due to rounding. (1) On December 31, 2016, Merck and Sanofi terminated their equally-owned joint venture, SPMSD, which marketed vaccines in most major European markets (see Note 9). Accordingly, vaccine sales in 2018 and 2017 include sales in the European markets that were previously part of SPMSD. Amounts for 2016 do not include sales of vaccines sold through SPMSD, the results of which are reflected in equity income from affiliates included in Other (income) expense, net . Amounts for 2016 do, however, include supply sales to SPMSD. (2) Other pharmaceutical primarily reflects sales of other human health pharmaceutical products, including products within the franchises not listed separately. (3) Represents the non-reportable segments of Healthcare Services and Alliances. (4) Other is primarily comprised of miscellaneous corporate revenues, including revenue hedging activities, as well as third-party manufacturing sales. Other in 2018, 2017 and 2016 also includes approximately $95 million , $85 million and $170 million , respectively, related to the sale of the marketing rights to certain products. Consolidated revenues by geographic area where derived are as follows: Years Ended December 31 2018 2017 2016 United States $ 18,212 $ 17,424 $ 18,478 Europe, Middle East and Africa 12,213 11,478 10,953 Japan 3,212 3,122 2,846 Asia Pacific (other than Japan and China) 2,909 2,751 2,483 Latin America 2,415 2,339 2,155 China 2,184 1,586 1,435 Other 1,149 1,422 1,457 $ 42,294 $ 40,122 $ 39,807 A reconciliation of segment profits to Income before taxes is as follows: Years Ended December 31 2018 2017 2016 Segment profits: Pharmaceutical segment $ 24,292 $ 22,495 $ 22,141 Animal Health segment 1,659 1,552 1,357 Other segments 103 275 146 Total segment profits 26,054 24,322 23,644 Other profits 6 26 481 Unallocated: Interest income 343 385 328 Interest expense (772 ) (754 ) (693 ) Depreciation and amortization (1,334 ) (1,378 ) (1,585 ) Research and development (8,853 ) (9,481 ) (9,218 ) Amortization of purchase accounting adjustments (2,664 ) (3,056 ) (3,692 ) Restructuring costs (632 ) (776 ) (651 ) Charge related to termination of collaboration agreement with Samsung (423 ) — — Loss on extinguishment of debt — (191 ) — Gain on sale of certain migraine clinical development programs — — 100 Charge related to the settlement of worldwide Keytruda patent litigation — — (625 ) Other unallocated, net (3,024 ) (2,576 ) (3,430 ) $ 8,701 $ 6,521 $ 4,659 Pharmaceutical segment profits are comprised of segment sales less standard costs, as well as selling, general and administrative expenses and research and development costs directly incurred by the segment. Animal Health segment profits are comprised of segment sales, less all cost of sales, as well as selling, general and administrative expenses and research and development costs directly incurred by the segment. For internal management reporting presented to the chief operating decision maker, Merck does not allocate the remaining cost of sales not included in segment profits as described above, research and development expenses incurred in Merck Research Laboratories, the Company’s research and development division that focuses on human health-related activities, or general and administrative expenses, nor the cost of financing these activities. Separate divisions maintain responsibility for monitoring and managing these costs, including depreciation related to fixed assets utilized by these divisions and, therefore, they are not included in segment profits. In addition, costs related to restructuring activities, as well as the amortization of purchase accounting adjustments are not allocated to segments. Other profits are primarily comprised of miscellaneous corporate profits, as well as operating profits related to third-party manufacturing sales. Other unallocated, net includes expenses from corporate and manufacturing cost centers, goodwill and other intangible asset impairment charges, gains or losses on sales of businesses, expense or income related to changes in the estimated fair value of liabilities for contingent consideration, and other miscellaneous income or expense items. In 2018, the Company adopted a new accounting standard related to the classification of certain defined benefit plan costs (see Note 2), which resulted in a change to the measurement of segment profits. Net periodic benefit cost (credit) other than service cost is no longer included as a component of segment profits. Prior period amounts have been recast to conform to the new presentation. Equity (income) loss from affiliates and depreciation and amortization included in segment profits is as follows: Pharmaceutical Animal Health All Other Total Year Ended December 31, 2018 Included in segment profits: Equity (income) loss from affiliates $ 4 $ — $ — $ 4 Depreciation and amortization 243 82 10 335 Year Ended December 31, 2017 Included in segment profits: Equity (income) loss from affiliates $ 7 $ — $ — $ 7 Depreciation and amortization 125 75 12 212 Year Ended December 31, 2016 Included in segment profits: Equity (income) loss from affiliates $ (105 ) $ — $ — $ (105 ) Depreciation and amortization 160 10 13 183 Property, plant and equipment, net, by geographic area where located is as follows: December 31 2018 2017 2016 United States $ 8,306 $ 8,070 $ 8,114 Europe, Middle East and Africa 3,706 3,151 2,732 Asia Pacific (other than Japan and China) 684 632 623 Latin America 264 271 234 China 167 150 152 Japan 159 158 164 Other 5 7 7 $ 13,291 $ 12,439 $ 12,026 The Company does not disaggregate assets on a products and services basis for internal management reporting and, therefore, such information is not presented.

Summary of Accounting Policies

Summary of Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation — The consolidated financial statements include the accounts of the Company and all of its subsidiaries in which a controlling interest is maintained. Intercompany balances and transactions are eliminated. Controlling interest is determined by majority ownership interest and the absence of substantive third-party participating rights or, in the case of variable interest entities, by majority exposure to expected losses, residual returns or both. For those consolidated subsidiaries where Merck ownership is less than 100%, the outside shareholders’ interests are shown as Noncontrolling interests in equity. Investments in affiliates over which the Company has significant influence but not a controlling interest, such as interests in entities owned equally by the Company and a third party that are under shared control, are carried on the equity basis.
Acquisitions	Acquisitions — In a business combination, the acquisition method of accounting requires that the assets acquired and liabilities assumed be recorded as of the date of the acquisition at their respective fair values with limited exceptions. Assets acquired and liabilities assumed in a business combination that arise from contingencies are generally recognized at fair value. If fair value cannot be determined, the asset or liability is recognized if probable and reasonably estimable; if these criteria are not met, no asset or liability is recognized. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Accordingly, the Company may be required to value assets at fair value measures that do not reflect the Company’s intended use of those assets. Any excess of the purchase price (consideration transferred) over the estimated fair values of net assets acquired is recorded as goodwill. Transaction costs and costs to restructure the acquired company are expensed as incurred. The operating results of the acquired business are reflected in the Company’s consolidated financial statements after the date of the acquisition. If the Company determines the assets acquired do not meet the definition of a business under the acquisition method of accounting, the transaction will be accounted for as an acquisition of assets rather than a business combination and, therefore, no goodwill will be recorded. In an asset acquisition, acquired in-process research and development (IPR&D) with no alternative future use is charged to expense and contingent consideration is not recognized at the acquisition date.
Foreign Currency Translation	Foreign Currency Translation — The net assets of international subsidiaries where the local currencies have been determined to be the functional currencies are translated into U.S. dollars using current exchange rates. The U.S. dollar effects that arise from translating the net assets of these subsidiaries at changing rates are recorded in the foreign currency translation account, which is included in Accumulated other comprehensive income (loss) ( AOCI ) and reflected as a separate component of equity. For those subsidiaries that operate in highly inflationary economies and for those subsidiaries where the U.S. dollar has been determined to be the functional currency, non-monetary foreign currency assets and liabilities are translated using historical rates, while monetary assets and liabilities are translated at current rates, with the U.S. dollar effects of rate changes included in Other (income) expense, net .
Cash Equivalents	Cash Equivalents — Cash equivalents are comprised of certain highly liquid investments with original maturities of less than three months.
Inventories	Inventories — Inventories are valued at the lower of cost or net realizable value. The cost of a substantial majority of U.S. pharmaceutical and vaccine inventories is determined using the last-in, first-out (LIFO) method for both financial reporting and tax purposes. The cost of all other inventories is determined using the first-in, first-out (FIFO) method. Inventories consist of currently marketed products, as well as certain inventories produced in preparation for product launches that are considered to have a high probability of regulatory approval. In evaluating the recoverability of inventories produced in preparation for product launches, the Company considers the likelihood that revenue will be obtained from the future sale of the related inventory together with the status of the product within the regulatory approval process.
Investments	Investments — Investments in marketable debt securities classified as available-for-sale are reported at fair value. Fair values of the Company’s investments in marketable debt securities are determined using quoted market prices in active markets for identical assets or liabilities or quoted prices for similar assets or liabilities or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Changes in fair value that are considered temporary are reported net of tax in Other Comprehensive Income ( OCI ). The Company considers available evidence in evaluating potential impairments of its investments in marketable debt securities, including the duration and extent to which fair value is less than cost. An other-than-temporary impairment has occurred if the Company does not expect to recover the entire amortized cost basis of the marketable debt security. If the Company does not intend to sell the impaired debt security, and it is not more likely than not it will be required to sell the debt security before the recovery of its amortized cost basis, the amount of the other-than-temporary impairment recognized in earnings, recorded in Other (income) expense, net , is limited to the portion attributed to credit loss. The remaining portion of the other-than-temporary impairment related to other factors is recognized in OCI . Realized gains and losses for debt securities are included in Other (income) expense, net . Investments in publicly traded equity securities are reported at fair value determined using quoted market prices in active markets for identical assets or quoted prices for similar assets or other inputs that are observable or can be corroborated by observable market data. Changes in fair value are included in Other (income) expense, net . Investments in equity securities without readily determinable fair values are recorded at cost, plus or minus subsequent observable price changes in orderly transactions for identical or similar investments, minus impairments. Such adjustments are recognized in Other (income) expense, net . Realized gains and losses for equity securities are included in Other (income) expense, net .
Revenue Recognition	Revenue Recognition — On January 1, 2018, the Company adopted ASU 2014-09, Revenue from Contracts with Customers , and subsequent amendments (ASC 606 or new guidance), using the modified retrospective method. Merck applied the new guidance to all contracts with customers within the scope of the standard that were in effect on January 1, 2018 and recognized the cumulative effect of initially applying the new guidance as an adjustment to the opening balance of retained earnings (see “ Recently Adopted Accounting Standards ” below). Comparative information for prior periods has not been restated and continues to be reported under the accounting standards in effect for those periods. The new guidance requires an entity to recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration that it expects to be entitled to in exchange for those goods or services. The new guidance introduces a 5-step model to recognize revenue when or as control is transferred: identify the contract with a customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when or as the performance obligations are satisfied. Changes to the Company’s revenue recognition policy as a result of adopting ASC 606 are described below. See Note 19 for disaggregated revenue disclosures. Recognition of revenue requires evidence of a contract, probable collection of sales proceeds and completion of substantially all performance obligations. Merck acts as the principal in substantially all of its customer arrangements and therefore records revenue on a gross basis. The majority of the Company’s contracts related to the Pharmaceutical and Animal Health segments have a single performance obligation - the promise to transfer goods. Shipping is considered immaterial in the context of the overall customer arrangement and damages or loss of goods in transit are rare. Therefore, shipping is not deemed a separately recognized performance obligation. The vast majority of revenues from sales of products are recognized at a point in time when control of the goods is transferred to the customer, which the Company has determined is when title and risks and rewards of ownership transfer to the customer and the Company is entitled to payment. Certain Merck entities, including U.S. entities, have contract terms under which control of the goods passes to the customer upon shipment; however, either pursuant to the terms of the contract or as a business practice, Merck retains responsibility for goods lost or damaged in transit. Prior to the adoption of the new standard, Merck would recognize revenue for these entities upon delivery of the goods. Under the new guidance, the Company is now recognizing revenue at time of shipment for these entities. The Company recognizes revenue from the sales of vaccines to the Federal government for placement into vaccine stockpiles in accordance with Securities and Exchange Commission (SEC) Interpretation , Commission Guidance Regarding Accounting for Sales of Vaccines and BioTerror Countermeasures to the Federal Government for Placement into the Pediatric Vaccine Stockpile or the Strategic National Stockpile . This interpretation allows companies to recognize revenue for sales of vaccines into U.S. government stockpiles even though these sales might not meet the criteria for revenue recognition under other accounting guidance. For businesses within the Company’s Healthcare Services segment and certain services in the Animal Health segment, revenue is recognized over time, generally ratably over the contract term as services are provided. These service revenues are not material. The nature of the Company’s business gives rise to several types of variable consideration including discounts and returns, which are estimated at the time of sale generally using the expected value method, although the most likely amount method is used for prompt pay discounts. In the United States, sales discounts are issued to customers at the point-of-sale, through an intermediary wholesaler (known as chargebacks), or in the form of rebates. Additionally, sales are generally made with a limited right of return under certain conditions. Revenues are recorded net of provisions for sales discounts and returns, which are established at the time of sale. In addition, revenues are recorded net of time value of money discounts if collection of accounts receivable is expected to be in excess of one year. The U.S. provision for aggregate customer discounts covering chargebacks and rebates was $10.7 billion in 2018, $10.7 billion in 2017 and $9.7 billion in 2016. Chargebacks are discounts that occur when a contracted customer purchases through an intermediary wholesaler. The contracted customer generally purchases product from the wholesaler at its contracted price plus a mark-up. The wholesaler, in turn, charges the Company back for the difference between the price initially paid by the wholesaler and the contract price paid to the wholesaler by the customer. The provision for chargebacks is based on expected sell-through levels by the Company’s wholesale customers to contracted customers, as well as estimated wholesaler inventory levels. Rebates are amounts owed based upon definitive contractual agreements or legal requirements with private sector and public sector (Medicaid and Medicare Part D) benefit providers, after the final dispensing of the product by a pharmacy to a benefit plan participant. The provision for rebates is based on expected patient usage, as well as inventory levels in the distribution channel to determine the contractual obligation to the benefit providers. The Company uses historical customer segment utilization mix, sales forecasts, changes to product mix and price, inventory levels in the distribution channel, government pricing calculations and prior payment history in order to estimate the expected provision. Amounts accrued for aggregate customer discounts are evaluated on a quarterly basis through comparison of information provided by the wholesalers, health maintenance organizations, pharmacy benefit managers, federal and state agencies, and other customers to the amounts accrued. The accrued balances relative to the provisions for chargebacks and rebates included in Accounts receivable and Accrued and other current liabilities were $245 million and $2.4 billion , respectively, at December 31, 2018 and were $198 million and $2.4 billion , respectively, at December 31, 2017 . Outside of the United States, variable consideration in the form of discounts and rebates are a combination of commercially-driven discounts in highly competitive product classes, discounts required to gain or maintain reimbursement, or legislatively mandated rebates. In certain European countries, legislatively mandated rebates are calculated based on an estimate of the government’s total unbudgeted spending and the Company’s specific payback obligation. Rebates may also be required based on specific product sales thresholds. The Company applies an estimated factor against its actual invoiced sales to represent the expected level of future discount or rebate obligations associated with the sale. The Company maintains a returns policy that allows its U.S. pharmaceutical customers to return product within a specified period prior to and subsequent to the expiration date (generally, three to six months before and 12 months after product expiration). The estimate of the provision for returns is based upon historical experience with actual returns. Additionally, the Company considers factors such as levels of inventory in the distribution channel, product dating and expiration period, whether products have been discontinued, entrance in the market of generic competition, changes in formularies or launch of over-the-counter products, among others. Outside of the United States, returns are only allowed in certain countries on a limited basis. Merck’s payment terms for U.S. pharmaceutical customers are typically net 36 days from receipt of invoice and for U.S. animal health customers are typically net 30 days from receipt of invoice; however, certain products, including Keytruda , have longer payment terms up to 90 days. Outside of the United States, payment terms are typically 30 days to 90 days, although certain markets have longer payment terms.
Depreciation	Depreciation — Depreciation is provided over the estimated useful lives of the assets, principally using the straight-line method. For tax purposes, accelerated tax methods are used. The estimated useful lives primarily range from 25 to 45 years for Buildings , and from 3 to 15 years for Machinery, equipment and office furnishings .
Advertising and Promotion Costs	Advertising and Promotion Costs — Advertising and promotion costs are expensed as incurred.
Software Capitalization	Software Capitalization — The Company capitalizes certain costs incurred in connection with obtaining or developing internal-use software including external direct costs of material and services, and payroll costs for employees directly involved with the software development. Capitalized software costs are included in Property, plant and equipment and amortized beginning when the software project is substantially complete and the asset is ready for its intended use. Capitalized software costs associated with projects that are being amortized over 6 to 10 years (including the Company’s on-going multi-year implementation of an enterprise-wide resource planning system) were $439 million and $449 million , net of accumulated amortization at December 31, 2018 and 2017 , respectively. All other capitalized software costs are being amortized over periods ranging from 3 to 5 years. Costs incurred during the preliminary project stage and post-implementation stage, as well as maintenance and training costs, are expensed as incurred.
Goodwill	Goodwill — Goodwill represents the excess of the consideration transferred over the fair value of net assets of businesses acquired. Goodwill is assigned to reporting units and evaluated for impairment on at least an annual basis, or more frequently if impairment indicators exist, by first assessing qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If the Company concludes it is more likely than not that the fair value of a reporting unit is less than its carrying amount, a quantitative fair value test is performed. If the carrying value of a reporting unit is greater than its fair value, a goodwill impairment charge will be recorded for the difference (up to the carrying value of goodwill).
Acquired Intangibles	Acquired Intangibles — Acquired intangibles include products and product rights, tradenames and patents, which are initially recorded at fair value, assigned an estimated useful life, and amortized primarily on a straight-line basis over their estimated useful lives ranging from 2 to 20 years (see Note 8). The Company periodically evaluates whether current facts or circumstances indicate that the carrying values of its acquired intangibles may not be recoverable. If such circumstances are determined to exist, an estimate of the undiscounted future cash flows of these assets, or appropriate asset groupings, is compared to the carrying value to determine whether an impairment exists. If the asset is determined to be impaired, the loss is measured based on the difference between the carrying value of the intangible asset and its fair value, which is determined based on the net present value of estimated future cash flows.
Acquired In-Process Research and Development	Acquired In-Process Research and Development — Acquired IPR&D that the Company acquires through business combinations represents the fair value assigned to incomplete research projects which, at the time of acquisition, have not reached technological feasibility. The amounts are capitalized and are accounted for as indefinite-lived intangible assets, subject to impairment testing until completion or abandonment of the projects. Upon successful completion of each project, Merck will make a determination as to the then-useful life of the intangible asset, generally determined by the period in which the substantial majority of the cash flows are expected to be generated, and begin amortization. The Company tests IPR&D for impairment at least annually, or more frequently if impairment indicators exist, by first assessing qualitative factors to determine whether it is more likely than not that the fair value of the IPR&D intangible asset is less than its carrying amount. If the Company concludes it is more likely than not that the fair value is less than the carrying amount, a quantitative test that compares the fair value of the IPR&D intangible asset with its carrying value is performed. If the fair value is less than the carrying amount, an impairment loss is recognized in operating results.
Contingent Consideration	Contingent Consideration — Certain of the Company’s business acquisitions involve the potential for future payment of consideration that is contingent upon the achievement of performance milestones, including product development milestones and royalty payments on future product sales. The fair value of contingent consideration liabilities is determined at the acquisition date using unobservable inputs. These inputs include the estimated amount and timing of projected cash flows, the probability of success (achievement of the contingent event) and the risk-adjusted discount rate used to present value the probability-weighted cash flows. Subsequent to the acquisition date, at each reporting period, the contingent consideration liability is remeasured at current fair value with changes (either expense or income) recorded in earnings.
Research and Development	Research and Development — Research and development is expensed as incurred. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. Research and development expenses include restructuring costs and IPR&D impairment charges. In addition, research and development expenses include expense or income related to changes in the estimated fair value measurement of liabilities for contingent consideration. Research and development expenses also include upfront and milestone payments related to asset acquisitions and licensing transactions involving clinical development programs that have not yet received regulatory approval.
Collaborative Arrangements	Collaborative Arrangements — Merck has entered into collaborative arrangements that provide the Company with varying rights to develop, produce and market products together with its collaborative partners. When Merck is the principal on sales transactions with third parties, the Company recognizes sales, cost of sales and selling, general and administrative expenses on a gross basis. Profit sharing amounts it pays to its collaborative partners are recorded within Cost of sales . When the collaborative partner is the principal on sales transactions with third parties, the Company records profit sharing amounts received from its collaborative partners as alliance revenue (within Sales ). Alliance revenue is recorded net of cost of sales and includes an adjustment to share commercialization costs between the partners in accordance with the collaboration agreement. The adjustment is determined by comparing the commercialization costs Merck has incurred directly and reported within Selling, general and administrative expenses with the costs the collaborative partner has incurred. Research and development costs Merck incurs related to collaborations are recorded within Research and development expenses. Cost reimbursements to the collaborative partner or payments received from the collaborative partner to share these costs pursuant to the terms of the collaboration agreements are recorded as increases or decreases to Research and development expenses. In addition, the terms of the collaboration agreements may require the Company to make payments based upon the achievement of certain developmental, regulatory approval or commercial milestones. Upfront and milestone payments payable by Merck to collaborative partners prior to regulatory approval are expensed as incurred and included in Research and development expenses. Payments due to collaborative partners upon or subsequent to regulatory approval are capitalized and amortized over the estimated useful life of the corresponding intangible asset to Cost of sales provided that future cash flows support the amounts capitalized. Sales-based milestones payable by Merck to collaborative partners are accrued when probable of being achieved and capitalized, subject to cumulative amortization catch-up. The amortization catch-up is calculated either from the time of the first regulatory approval for indications that were unapproved at the time the collaboration was formed, or from time of the formation of the collaboration for approved products. The related intangible asset that is recognized is amortized to Cost of sales over its remaining useful life, subject to impairment testing.
Share-Based Compensation	Share-Based Compensation — The Company expenses all share-based payments to employees over the requisite service period based on the grant-date fair value of the awards.
Restructuring Costs	Restructuring Costs — The Company records liabilities for costs associated with exit or disposal activities in the period in which the liability is incurred. In accordance with existing benefit arrangements, employee termination costs are accrued when the restructuring actions are probable and estimable. When accruing these costs, the Company will recognize the amount within a range of costs that is the best estimate within the range. When no amount within the range is a better estimate than any other amount, the Company recognizes the minimum amount within the range. Costs for one-time termination benefits in which the employee is required to render service until termination in order to receive the benefits are recognized ratably over the future service period.
Contingencies and Legal Defense Costs	Contingencies and Legal Defense Costs — The Company records accruals for contingencies and legal defense costs expected to be incurred in connection with a loss contingency when it is probable that a liability has been incurred and the amount can be reasonably estimated.
Taxes on Income	Taxes on Income — Deferred taxes are recognized for the future tax effects of temporary differences between financial and income tax reporting based on enacted tax laws and rates. The Company evaluates tax positions to determine whether the benefits of tax positions are more likely than not of being sustained upon audit based on the technical merits of the tax position. For tax positions that are more likely than not of being sustained upon audit, the Company recognizes the largest amount of the benefit that is greater than 50% likely of being realized upon ultimate settlement in the financial statements. For tax positions that are not more likely than not of being sustained upon audit, the Company does not recognize any portion of the benefit in the financial statements. The Company recognizes interest and penalties associated with uncertain tax positions as a component of Taxes on income in the Consolidated Statement of Income.
Use of Estimates	Use of Estimates — The consolidated financial statements are prepared in conformity with accounting principles generally accepted in the United States (GAAP) and, accordingly, include certain amounts that are based on management’s best estimates and judgments. Estimates are used when accounting for amounts recorded in connection with acquisitions, including initial fair value determinations of assets and liabilities, primarily IPR&D, other intangible assets and contingent consideration, as well as subsequent fair value measurements. Additionally, estimates are used in determining such items as provisions for sales discounts and returns, depreciable and amortizable lives, recoverability of inventories, including those produced in preparation for product launches, amounts recorded for contingencies, environmental liabilities, accruals for contingent sales-based milestone payments and other reserves, pension and other postretirement benefit plan assumptions, share-based compensation assumptions, restructuring costs, impairments of long-lived assets (including intangible assets and goodwill) and investments, and taxes on income. Because of the uncertainty inherent in such estimates, actual results may differ from these estimates.
Reclassifications	Reclassifications — Certain reclassifications have been made to prior year amounts to conform to the current year presentation.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards — In May 2014, the Financial Accounting Standards Board (FASB) issued amended accounting guidance on revenue recognition (ASU 2014-09) that applies to all contracts with customers. The objective of the new guidance is to improve comparability of revenue recognition practices across entities and to provide more useful information to users of financial statements through improved disclosure requirements. The new standard permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of adopting the guidance being recognized at the date of initial application (modified retrospective method). The new standard was effective as of January 1, 2018 and was adopted using the modified retrospective method. The Company recorded a cumulative-effect adjustment upon adoption increasing Retained earnings by $5 million . In January 2016, the FASB issued revised guidance for the accounting and reporting of financial instruments (ASU 2016-01) and in 2018 issued related technical corrections (ASU 2018-03). The new guidance requires that equity investments with readily determinable fair values currently classified as available for sale be measured at fair value with changes in fair value recognized in net income. The Company has elected to measure equity investments without readily determinable fair values at cost, adjusted for subsequent observable price changes and less impairments, which will be recognized in net income. The new guidance also changed certain disclosure requirements. ASU 2016-01 was effective as of January 1, 2018 and was adopted using a modified retrospective approach. The Company recorded a cumulative-effect adjustment upon adoption increasing Retained earnings by $8 million . ASU 2018-03 was also adopted as of January 1, 2018 on a prospective basis and did not result in any additional impacts upon adoption. In October 2016, the FASB issued guidance on the accounting for the income tax consequences of intra-entity transfers of assets other than inventory (ASU 2016-16). The new guidance requires the recognition of the income tax consequences of an intra-entity transfer of an asset (with the exception of inventory) when the intra-entity transfer occurs, replacing the prohibition against doing so. The current exception to defer the recognition of any tax impact on the transfer of inventory within the consolidated entity until it is sold to a third party remains unaffected. The new standard was effective as of January 1, 2018 and was adopted using a modified retrospective approach. The Company recorded a cumulative-effect adjustment upon adoption increasing Retained earnings by $54 million with a corresponding decrease to Deferred Income Taxes . In August 2017, the FASB issued new guidance on hedge accounting (ASU 2017-12) that is intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. The new guidance makes more financial and nonfinancial hedging strategies eligible for hedge accounting, amends the presentation and disclosure requirements, and changes how companies assess effectiveness. The Company elected to early adopt this guidance as of January 1, 2018 on a modified retrospective basis. The new guidance was applied to all existing hedges as of the adoption date. For fair value hedges of interest rate risk outstanding as of the date of adoption, the Company recorded a cumulative-effect adjustment upon adoption to the basis adjustment on the hedged item resulting from applying the benchmark component of the coupon guidance. This adjustment decreased Retained earnings by $11 million . Also, in accordance with the transition provisions of ASU 2017-12, the Company was required to eliminate the separate measurement of ineffectiveness for its cash flow hedging instruments existing as of the adoption date through a cumulative-effect adjustment to retained earnings; however, all such amounts were de minimis . In February 2018, the FASB issued new guidance to address a narrow-scope financial reporting issue that arose as a consequence of the Tax Cuts and Jobs Act of 2017 (TCJA) (ASU 2018-02). Existing guidance requires that deferred tax liabilities and assets be adjusted for a change in tax laws or rates with the effect included in income from continuing operations in the reporting period that includes the enactment date. That guidance is applicable even in situations in which the related income tax effects of items in accumulated other comprehensive income were originally recognized in other comprehensive income (rather than in net income), such as amounts related to benefit plans and hedging activity. As a result, the tax effects of items within accumulated other comprehensive income do not reflect the appropriate tax rate (the difference is referred to as stranded tax effects). The new guidance allows for a reclassification of the stranded tax effects resulting from the TCJA from accumulated other comprehensive income to retained earnings thereby eliminating these stranded tax effects. The Company elected to early adopt the new guidance in the first quarter of 2018 and reclassified the stranded income tax effects of the TCJA, increasing Accumulated other comprehensive loss in the amount of $266 million with a corresponding increase to Retained earnings (see Note 18). The Company’s policy for releasing disproportionate income tax effects from Accumulated other comprehensive loss is to utilize the item-by-item approach. The impact of adopting the above standards is as follows: ($ in millions) ASU 2014-09 (Revenue) ASU 2016-01 (Financial Instruments) ASU 2016-16 (Intra-Entity Transfers of Assets Other than Inventory) ASU 2017-12 (Derivatives and Hedging) ASU 2018-02 (Reclassification of Certain Tax Effects) Total Assets - Increase (Decrease) Accounts receivable $ 5 $ 5 Liabilities - Increase (Decrease) Income Taxes Payable (3 ) (3 ) Debt 14 14 Deferred Income Taxes (54 ) (54 ) Equity - Increase (Decrease) Retained earnings 5 8 54 (11 ) 266 322 Accumulated other comprehensive loss (8 ) (266 ) (274 ) In March 2017, the FASB issued amended guidance on retirement benefits (ASU 2017-07) related to net periodic benefit cost for defined benefit plans that requires entities to (1) disaggregate the current service cost component from the other components of net benefit cost and present it with other employee compensation costs in the income statement within operations if such a subtotal is presented; (2) present the other components of net benefit cost separately in the income statement and outside of income from operations; and (3) only capitalize the service cost component when applicable. The Company adopted the new standard as of January 1, 2018 using a retrospective transition method as to the requirement for separate presentation in the income statement of service costs and other components, and a prospective transition method as to the requirement to limit the capitalization of benefit costs to the service cost component. The Company utilized a practical expedient that permits it to use the amounts disclosed in its pension and other postretirement benefit plan note for the prior comparative periods as the estimation basis for applying the retrospective presentation requirements. Upon adoption, net periodic benefit cost (credit) other than service cost of $(512) million and $(531) million for the years ended December 31, 2017 and 2016, respectively, was reclassified to Other (income) expense, net from the previous classification within Cost of sales , Selling, general and administrative expenses and Research and development expenses (see Note 15). In August 2016, the FASB issued guidance on the classification of certain cash receipts and payments in the statement of cash flows intended to reduce diversity in practice. The Company adopted the new standard effective as of January 1, 2018 using a retrospective application. There were no changes to the presentation of the Consolidated Statement of Cash Flows in the previous years presented as a result of adopting the new standard. In November 2016, the FASB issued guidance requiring that amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The new standard was effective as of January 1, 2018 and was adopted using a retrospective application. The adoption of the new guidance did not have a material effect on the Company’s Consolidated Statement of Cash Flows. In May 2017, the FASB issued guidance clarifying when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The Company adopted the new standard effective as of January 1, 2018 and will apply the new guidance to future share-based payment award modifications should they occur. In January 2017, the FASB issued guidance that provides for the elimination of Step 2 from the goodwill impairment test. Under the new guidance, impairment charges are recognized to the extent the carrying amount of a reporting unit exceeds its fair value with certain limitations. The Company adopted the new standard in the fourth quarter of 2018 and applied the new guidance for purposes of its fourth quarter goodwill impairment assessment. The adoption of the new guidance had an immaterial effect on its consolidated financial statements. Recently Issued Accounting Standards Not Yet Adopted — In February 2016, the FASB issued new accounting guidance for the accounting and reporting of leases and subsequently issued several updates to the new guidance. The new guidance requires that lessees recognize a right-of-use asset and a lease liability recorded on the balance sheet for each of its leases (other than leases that meet the definition of a short-term lease). Leases will be classified as either operating or finance. Operating leases will result in straight-line expense in the income statement (similar to current operating leases) while finance leases will result in more expense being recognized in the earlier years of the lease term (similar to current capital leases). The new standard is effective as of January 1, 2019 and will be adopted using a modified retrospective approach. Merck will elect the transition method that allows for application of the standard at the adoption date rather than at the beginning of the earliest comparative period presented in the financial statements. The Company intends to elect available practical expedients. Merck has implemented a lease accounting software application and has completed data validation of the Company’s portfolio of leases, including its assessment of potential embedded leases. Upon adoption, the Company anticipates it will recognize approximately $1 billion of additional assets and corresponding liabilities on its consolidated balance sheet, subject to finalization. In June 2016, the FASB issued amended guidance on the accounting for credit losses on financial instruments. The guidance introduces an expected loss model for estimating credit losses, replacing the incurred loss model. The new guidance also changes the impairment model for available-for-sale debt securities, requiring the use of an allowance to record estimated credit losses (and subsequent recoveries). The new guidance is effective for interim and annual periods beginning in 2020, with earlier application permitted in 2019. The new guidance is to be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings in the beginning of the period of adoption. The Company is currently evaluating the impact of adoption on its consolidated financial statements. In April 2018, the FASB issued new guidance on the accounting for costs incurred to implement a cloud computing arrangement that is considered a service arrangement. The new guidance requires the capitalization of such costs, aligning it with the accounting for costs associated with developing or obtaining internal-use software. The new guidance is effective for interim and annual periods beginning in 2020. Early adoption is permitted, including adoption in any interim period. Prospective adoption for eligible costs incurred on or after the date of adoption or retrospective adoption is permitted. The Company is currently evaluating the impact of adoption on its consolidated financial statements and may elect to early adopt this guidance. In November 2018, the FASB issued new guidance for collaborative arrangements intended to reduce diversity in practice by clarifying whether certain transactions between collaborative arrangement participants should be accounted for under the recently issued guidance on revenue recognition (ASC 606). The new guidance is effective for interim and annual periods beginning in 2020. Early adoption is permitted, including adoption in any interim period. The new guidance is to be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings. The Company is currently evaluating the impact of adoption on its consolidated financial statements.

Summary of Accounting Policie_2

Summary of Accounting Policies Summary of Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Impact of Adopting New Standards	The following table provides the effects of adopting ASC 606 on the Consolidated Statement of Income: Year Ended December 31, 2018 As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Sales $ 42,294 $ (2 ) $ 42,292 Cost of sales 13,509 (6 ) 13,503 Income before taxes 8,701 4 8,705 Taxes on income 2,508 1 2,509 Net income attributable to Merck & Co., Inc. 6,220 3 6,223 The following table provides the effects of adopting ASC 606 on the Consolidated Balance Sheet: December 31, 2018 As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Assets Accounts receivable $ 7,071 $ (13 ) $ 7,058 Inventories 5,440 7 5,447 Liabilities Accrued and other current liabilities 10,151 (3 ) 10,148 Income taxes payable 1,971 (1 ) 1,970 Equity Retained earnings 42,579 (2 ) 42,577 The impact of adopting the above standards is as follows: ($ in millions) ASU 2014-09 (Revenue) ASU 2016-01 (Financial Instruments) ASU 2016-16 (Intra-Entity Transfers of Assets Other than Inventory) ASU 2017-12 (Derivatives and Hedging) ASU 2018-02 (Reclassification of Certain Tax Effects) Total Assets - Increase (Decrease) Accounts receivable $ 5 $ 5 Liabilities - Increase (Decrease) Income Taxes Payable (3 ) (3 ) Debt 14 14 Deferred Income Taxes (54 ) (54 ) Equity - Increase (Decrease) Retained earnings 5 8 54 (11 ) 266 322 Accumulated other comprehensive loss (8 ) (266 ) (274 )

Collaborative Arrangements (Tab

Collaborative Arrangements (Tables)	12 Months Ended
	Dec. 31, 2018
Collaborative Arrangements [Abstract]
Schedule of Collaborative Arrangements	Summarized information related to this collaboration is as follows: Years Ended December 31 2018 2017 2016 Net product sales recorded by Merck $ 190 $ 149 $ 88 Merck’s profit share from sales in Bayer’s marketing territories 139 151 81 Total sales 329 300 169 Cost of sales (1) 216 99 133 Selling, general and administrative 35 27 26 Research and development 127 101 82 December 31 2018 2017 Receivables from Bayer included in Other current assets $ 32 $ 33 Payables to Bayer included in Accrued and other current liabilities (2) — 350 Payables to Bayer included in Other Noncurrent Liabilities (2) 375 — (1) Includes amortization of intangible assets. (2) Includes accrued milestone payments. Summarized information related to this collaboration is as follows: Year Ended December 31 2018 Alliance revenue $ 149 Cost of sales (1) 39 Selling, general and administrative 13 Research and development (2) 1,489 December 31 2018 Receivables from Eisai included in Other current assets $ 71 Payables to Eisai included in Accrued and other current liabilities (3) 375 Payables to Eisai included in Other Noncurrent Liabilities (3) 543 (1) Represents amortization of capitalized milestone payments. (2) Includes $1.4 billion related to the upfront payment and future option payments. (3) Includes accrued milestone and option payments. nt testing. Summarized information related to this collaboration is as follows: Years Ended December 31 2018 2017 Alliance revenue $ 187 $ 20 Cost of sales (1) 93 4 Selling, general and administrative 48 1 Research and development (2) 152 2,419 December 31 2018 2017 Receivables from AstraZeneca included in Other current assets $ 52 $ 12 Payables to AstraZeneca included in Accrued and other current liabilities (3) 405 543 Payables to AstraZeneca included Other Noncurrent Liabilities (3) 250 100 (1) Represents amortization of capitalized milestone payments. (2) Amount for 2017 includes $2.35 billion related to the upfront payment and future license option payments. (3) Includes accrued milestone and license option payments.

Restructuring (Tables)

Restructuring (Tables)	12 Months Ended
	Dec. 31, 2018
Restructuring and Related Activities [Abstract]
Charges Related to Restructuring Program Activities by Type of Cost	The following table summarizes the charges related to restructuring program activities by type of cost: Separation Costs Accelerated Depreciation Other Total Year Ended December 31, 2018 Cost of sales $ — $ 10 $ 11 $ 21 Selling, general and administrative — 2 1 3 Research and development — (13 ) 15 2 Restructuring costs 473 — 159 632 $ 473 $ (1 ) $ 186 $ 658 Year Ended December 31, 2017 Cost of sales $ — $ 52 $ 86 $ 138 Selling, general and administrative — 2 — 2 Research and development — 6 5 11 Restructuring costs 552 — 224 776 $ 552 $ 60 $ 315 $ 927 Year Ended December 31, 2016 Cost of sales $ — $ 77 $ 104 $ 181 Selling, general and administrative — 8 87 95 Research and development — 142 — 142 Restructuring costs 216 — 435 651 $ 216 $ 227 $ 626 $ 1,069
Charges and Spending Relating to Restructuring Activities by Program	The following table summarizes the charges and spending relating to restructuring program activities: Separation Costs Accelerated Depreciation Other Total Restructuring reserves January 1, 2017 $ 395 $ — $ 146 $ 541 Expenses 552 60 315 927 (Payments) receipts, net (328 ) — (394 ) (722 ) Non-cash activity — (60 ) 61 1 Restructuring reserves December 31, 2017 619 — 128 747 Expenses 473 (1 ) 186 658 (Payments) receipts, net (649 ) — (238 ) (887 ) Non-cash activity — 1 15 16 Restructuring reserves December 31, 2018 (1) $ 443 $ — $ 91 $ 534 (1) The remaining cash outlays are expected to be substantially completed by the end of 2020.

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Effect of Net Investment Hedges	The effects of the Company’s net investment hedges on OCI and the Consolidated Statement of Income are shown below: Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income (1) Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing Years Ended December 31 2018 2017 2016 2018 2017 2016 Net Investment Hedging Relationships Foreign exchange contracts $ (18 ) $ — $ 2 $ (11 ) $ — $ (1 ) Euro-denominated notes (183 ) 520 (193 ) — — — (1) No amounts were reclassified from AOCI into income related to the sale of a subsidiary.
Summary of Interest Rate Derivatives	At December 31, 2018 , the Company was a party to 19 pay-floating, receive-fixed interest rate swap contracts designated as fair value hedges of fixed-rate notes in which the notional amounts match the amount of the hedged fixed-rate notes as detailed in the table below. 2018 Debt Instrument Par Value of Debt Number of Interest Rate Swaps Held Total Swap Notional Amount 1.85% notes due 2020 $ 1,250 5 $ 1,250 3.875% notes due 2021 1,150 5 1,150 2.40% notes due 2022 1,000 4 1,000 2.35% notes due 2022 1,250 5 1,250
Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block]	The table below presents the location of amounts recorded on the Consolidated Balance Sheet related to cumulative basis adjustments for fair value hedges as of December 31: Carrying Amount of Hedged Liabilities Cumulative Amount of Fair Value Hedging Adjustment Increase (Decrease) Included in the Carrying Amount 2018 2017 2018 2017 Balance Sheet Line Item in which Hedged Item is Included Loans payable and current portion of long-term debt $ — $ 983 $ — $ (17 ) Long-Term Debt (1) 4,560 5,146 (82 ) (41 ) (1) Amounts include hedging adjustment gains related to discontinued hedging relationships of $11 million at December 31, 2017.
Fair Value of Derivatives on a Gross Basis Segregated Between those Derivatives that are Designated as Hedging Instruments and those that are Not Designated as Hedging Instruments	Presented in the table below is the fair value of derivatives on a gross basis segregated between those derivatives that are designated as hedging instruments and those that are not designated as hedging instruments as of December 31: 2018 2017 Fair Value of Derivative U.S. Dollar Notional Fair Value of Derivative U.S. Dollar Notional Balance Sheet Caption Asset Liability Asset Liability Derivatives Designated as Hedging Instruments Interest rate swap contracts Other assets $ — $ — $ — $ 2 $ — $ 550 Interest rate swap contracts Accrued and other current liabilities — — — — 3 1,000 Interest rate swap contracts Other noncurrent liabilities — 81 4,650 — 52 4,650 Foreign exchange contracts Other current assets 263 — 6,222 51 — 4,216 Foreign exchange contracts Other assets 75 — 2,655 38 — 1,936 Foreign exchange contracts Accrued and other current liabilities — 7 774 — 71 2,014 Foreign exchange contracts Other noncurrent liabilities — 1 89 — 1 20 $ 338 $ 89 $ 14,390 $ 91 $ 127 $ 14,386 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts Other current assets $ 116 $ — $ 5,430 $ 39 $ — $ 3,778 Foreign exchange contracts Accrued and other current liabilities — 71 9,922 — 90 7,431 $ 116 $ 71 $ 15,352 $ 39 $ 90 $ 11,209 $ 454 $ 160 $ 29,742 $ 130 $ 217 $ 25,595
Information on Derivative Positions Subject to Master Netting Arrangements as if they were Presented on a Net Basis	The following table provides information on the Company’s derivative positions subject to these master netting arrangements as if they were presented on a net basis, allowing for the right of offset by counterparty and cash collateral exchanged per the master agreements and related credit support annexes at December 31: 2018 2017 Asset Liability Asset Liability Gross amounts recognized in the consolidated balance sheet $ 454 $ 160 $ 130 $ 217 Gross amount subject to offset in master netting arrangements not offset in the consolidated balance sheet (121 ) (121 ) (94 ) (94 ) Cash collateral received (107 ) — (3 ) — Net amounts $ 226 $ 39 $ 33 $ 123
Location and Pretax Gain or Loss Amounts for Derivatives	The table below provides information regarding the location and amount of pretax (gains) losses of derivatives designated in fair value or cash flow hedging relationships: Sales Other (income) expense, net (1) Other comprehensive income (loss) Years Ended December 31 2018 2017 2016 2018 2017 2016 2018 2017 2016 Financial Statement Line Items in which Effects of Fair Value or Cash Flow Hedges are Recorded $ 42,294 $ 40,122 $ 39,807 $ (402 ) (500 ) 189 $ (361 ) $ 316 $ (1,078 ) (Gain) loss on fair value hedging relationships Interest rate swap contracts Hedged items — — — (27 ) (48 ) (29 ) — — — Derivatives designated as hedging instruments — — — 50 12 (35 ) — — — Impact of cash flow hedging relationships Foreign exchange contracts Amount of gain (loss) recognized in OCI on derivatives — — — — — — 228 (562 ) 210 (Decrease) increase in Sales as a result of AOCI reclassifications (160 ) 138 311 — — — 160 (138 ) (311 ) (1) Interest expense is a component of Other (income) expense, net.
Income Statement Effects of Derivatives Not Designated as Hedging Instruments	The table below provides information regarding the income statement effects of derivatives not designated as hedging instruments: Amount of Derivative Pretax (Gain) Loss Recognized in Income Years Ended December 31 Income Statement Caption 2018 2017 2016 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts (1) Other (income) expense, net $ (260 ) $ 110 $ 132 Foreign exchange contracts (2) Sales (8 ) (3 ) — (1) These derivative contracts mitigate changes in the value of remeasured foreign currency denominated monetary assets and liabilities attributable to changes in foreign currency exchange rates. (2) These derivative contracts serve as economic hedges of forecasted transactions.
Information on Investments in Debt and Equity Securities	Information on investments in debt and equity securities at December 31 is as follows: 2018 2017 Fair Value Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized Gains Losses Gains Losses Corporate notes and bonds $ 4,920 $ 4,985 $ 3 $ (68 ) $ 9,806 $ 9,837 $ 9 $ (40 ) Asset-backed securities 1,275 1,285 1 (11 ) 1,542 1,548 1 (7 ) U.S. government and agency securities 892 895 2 (5 ) 2,042 2,059 — (17 ) Foreign government bonds 166 167 — (1 ) 733 739 — (6 ) Mortgage-backed securities 8 8 — — 626 634 1 (9 ) Commercial paper — — — — 159 159 — — Total debt securities 7,261 7,340 6 (85 ) 14,908 14,976 11 (79 ) Publicly traded equity securities (1) 456 275 265 16 (6 ) Total debt and publicly traded equity securities $ 7,717 $ 15,183 $ 15,241 $ 27 $ (85 )
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	Financial assets and liabilities measured at fair value on a recurring basis at December 31 are summarized below: Fair Value Measurements Using Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total 2018 2017 Assets Investments Corporate notes and bonds $ — $ 4,835 $ — $ 4,835 $ — $ 9,678 $ — $ 9,678 Asset-backed securities (1) — 1,253 — 1,253 — 1,476 — 1,476 U.S. government and agency securities — 731 — 731 68 1,767 — 1,835 Foreign government bonds — 166 — 166 — 732 — 732 Mortgage-backed securities — — — — — 547 — 547 Commercial paper — — — — — 159 — 159 Publicly traded equity securities 147 — — 147 104 — — 104 147 6,985 — 7,132 172 14,359 — 14,531 Other assets (2) U.S. government and agency securities 55 106 — 161 — 207 — 207 Corporate notes and bonds — 85 — 85 — 128 — 128 Asset-backed securities (1) — 22 — 22 — 66 — 66 Mortgage-backed securities — 8 — 8 — 79 — 79 Foreign government bonds — — — — — 1 — 1 Publicly traded equity securities 309 — — 309 171 — — 171 364 221 — 585 171 481 — 652 Derivative assets (3) Forward exchange contracts — 241 — 241 — 48 — 48 Purchased currency options — 213 — 213 — 80 — 80 Interest rate swaps — — — — — 2 — 2 — 454 — 454 — 130 — 130 Total assets $ 511 $ 7,660 $ — $ 8,171 $ 343 $ 14,970 $ — $ 15,313 Liabilities Other liabilities Contingent consideration $ — $ — $ 788 $ 788 $ — $ — $ 935 $ 935 Derivative liabilities (3) Interest rate swaps — 81 — 81 — 55 — 55 Forward exchange contracts — 74 — 74 — 162 — 162 Written currency options — 5 — 5 — — — — — 160 — 160 — 217 — 217 Total liabilities $ — $ 160 $ 788 $ 948 $ — $ 217 $ 935 $ 1,152 (1) Primarily all of the asset-backed securities are highly-rated (Standard & Poor’s rating of AAA and Moody’s Investors Service rating of Aaa), secured primarily by auto loan, credit card and student loan receivables, with weighted-average lives of primarily 5 years or less. (2) Investments included in other assets are restricted as to use, primarily for the payment of benefits under employee benefit plans. (3) The fair value determination of derivatives includes the impact of the credit risk of counterparties to the derivatives and the Company’s own credit risk, the effects of which were not significant.
Summarized Information about the Changes in Liabilities for Contingent Consideration	Summarized information about the changes in liabilities for contingent consideration is as follows: 2018 2017 Fair value January 1 $ 935 $ 891 Changes in estimated fair value (1) 89 141 Additions 8 3 Payments (244 ) (100 ) Fair value December 31 (2) $ 788 $ 935 (1) Recorded in Research and development expenses, Cost of sales and Other (income) expense, net . Includes cumulative translation adjustments. (2) Balance at December 31, 2018 includes $89 million recorded as a current liability for amounts expected to be paid within the next 12 months.

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories at December 31 consisted of: 2018 2017 Finished goods $ 1,658 $ 1,334 Raw materials and work in process 5,004 4,703 Supplies 194 201 Total (approximates current cost) 6,856 6,238 Increase to LIFO costs 1 45 $ 6,857 $ 6,283 Recognized as: Inventories $ 5,440 $ 5,096 Other assets 1,417 1,187

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill Activity by Segment	The following table summarizes goodwill activity by segment: Pharmaceutical Animal Health All Other Total Balance January 1, 2017 $ 16,075 $ 1,708 $ 379 $ 18,162 Acquisitions — 177 — 177 Impairments — — (38 ) (38 ) Other (1) (9 ) (8 ) — (17 ) Balance December 31, 2017 (2) 16,066 1,877 341 18,284 Acquisitions — 17 24 41 Impairments — — (144 ) (144 ) Other (1) 96 (24 ) — 72 Balance December 31, 2018 (2) $ 16,162 $ 1,870 $ 221 $ 18,253 (1) Other includes cumulative translation adjustments on goodwill balances and certain other adjustments. (2) Accumulated goodwill impairment losses at December 31, 2018 and 2017 were $369 million and $225 million , respectively.
Other Intangibles	Other intangibles at December 31 consisted of: 2018 2017 Gross Carrying Amount Accumulated Amortization Net Gross Carrying Amount Accumulated Amortization Net Products and product rights $ 46,615 $ 37,585 $ 9,030 $ 46,693 $ 34,950 $ 11,743 IPR&D 1,064 — 1,064 1,194 — 1,194 Tradenames 209 107 102 209 97 112 Other 2,403 1,168 1,235 2,035 901 1,134 $ 50,291 $ 38,860 $ 11,431 $ 50,131 $ 35,948 $ 14,183

Joint Ventures and Other Equi_2

Joint Ventures and Other Equity Method Affiliates (Tables)	12 Months Ended
	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Schedule of Fair Value of Assets Acquired and Liabilities Assumed	The net impact of the termination of the SPMSD joint venture is as follows: Products and product rights (8-year useful life) $ 936 Accounts receivable 133 Income taxes payable (221 ) Deferred income tax liabilities (147 ) Other, net 47 Net assets acquired 748 Consideration payable to Sanofi, net (392 ) Derecognition of Merck’s previously held equity investment in SPMSD (183 ) Increase in net assets 173 Merck’s share of restructuring costs related to the termination (77 ) Net gain on termination of SPMSD joint venture (1) $ 96 (1) Recorded in Other (income) expense, net .

Loans Payable, Long-Term Debt_2

Loans Payable, Long-Term Debt and Other Commitments (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	Long-term debt at December 31 consisted of: 2018 2017 2.75% notes due 2025 $ 2,490 $ 2,488 3.70% notes due 2045 1,974 1,973 2.80% notes due 2023 1,745 1,744 4.15% notes due 2043 1,237 1,237 1.85% notes due 2020 1,231 1,232 2.35% notes due 2022 1,214 1,220 1.125% euro-denominated notes due 2021 1,134 1,185 3.875% notes due 2021 1,132 1,140 1.875% euro-denominated notes due 2026 1,127 1,178 2.40% notes due 2022 983 993 6.50% notes due 2033 726 729 Floating-rate notes due 2020 699 699 0.50% euro-denominated notes due 2024 565 591 1.375% euro-denominated notes due 2036 561 587 2.50% euro-denominated notes due 2034 560 585 3.60% notes due 2042 490 489 6.55% notes due 2037 414 415 5.75% notes due 2036 338 338 5.95% debentures due 2028 306 306 5.85% notes due 2039 270 270 6.40% debentures due 2028 250 250 6.30% debentures due 2026 135 135 5.00% notes due 2019 — 1,260 Other 225 309 $ 19,806 $ 21,353

Equity (Tables)

Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Summary of Common Stock and Treasury Stock Transactions	A summary of common stock and treasury stock transactions (shares in millions) is as follows: 2018 2017 2016 Common Stock Treasury Stock Common Stock Treasury Stock Common Stock Treasury Stock Balance January 1 3,577 880 3,577 828 3,577 796 Purchases of treasury stock — 122 — 67 — 60 Issuances (1) — (17 ) — (15 ) — (28 ) Balance December 31 3,577 985 3,577 880 3,577 828 (1) Issuances primarily reflect activity under share-based compensation plans.

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Assumptions Used to Determine Weighted-Average Fair Value of Options Granted	The weighted average fair value of options granted in 2018 , 2017 and 2016 was $8.26 , $7.04 and $5.89 per option, respectively, and were determined using the following assumptions: Years Ended December 31 2018 2017 2016 Expected dividend yield 3.4 % 3.6 % 3.8 % Risk-free interest rate 2.9 % 2.0 % 1.4 % Expected volatility 19.1 % 17.8 % 19.6 % Expected life (years) 6.1 6.1 6.2
Summarized Information Relative to Stock Option Plan Activity	Summarized information relative to stock option plan activity (options in thousands) is as follows: Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding January 1, 2018 36,274 $ 46.77 Granted 3,520 58.15 Exercised (14,598 ) 40.51 Forfeited (1,389 ) 53.80 Outstanding December 31, 2018 23,807 $ 51.89 5.95 $ 584 Exercisable December 31, 2018 16,184 $ 48.85 4.82 $ 446
Additional Information Pertaining to Stock Option Plans	Additional information pertaining to stock option plans is provided in the table below: Years Ended December 31 2018 2017 2016 Total intrinsic value of stock options exercised $ 348 $ 236 $ 444 Fair value of stock options vested 29 30 28 Cash received from the exercise of stock options 591 499 939
Summary of Nonvested RSU and PSU Activity	A summary of nonvested RSU and PSU activity (shares in thousands) is as follows: RSUs PSUs Number of Shares Weighted Average Grant Date Fair Value Number of Shares Weighted Average Grant Date Fair Value Nonvested January 1, 2018 13,609 $ 59.32 1,868 $ 60.03 Granted 7,270 58.46 1,081 57.17 Vested (3,766 ) 59.66 (758 ) 57.59 Forfeited (985 ) 59.30 (152 ) 60.06 Nonvested December 31, 2018 16,128 $ 58.85 2,039 $ 59.42

Pension and Other Postretirem_2

Pension and Other Postretirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost	The net periodic benefit cost (credit) for pension and other postretirement benefit plans consisted of the following components: Pension Benefits U.S. International Other Postretirement Benefits Years Ended December 31 2018 2017 2016 2018 2017 2016 2018 2017 2016 Service cost $ 326 $ 312 $ 282 $ 238 $ 252 $ 238 $ 57 $ 57 $ 54 Interest cost 432 454 456 178 172 204 69 81 82 Expected return on plan assets (851 ) (862 ) (831 ) (431 ) (393 ) (382 ) (83 ) (78 ) (107 ) Amortization of unrecognized prior service cost (50 ) (53 ) (55 ) (13 ) (11 ) (11 ) (84 ) (98 ) (106 ) Net loss amortization 232 180 119 84 98 87 1 1 3 Termination benefits 19 44 23 2 4 4 3 8 4 Curtailments 10 3 5 1 (4 ) (1 ) (8 ) (31 ) (18 ) Settlements 5 — — 13 5 6 — — — Net periodic benefit cost (credit) $ 123 $ 78 $ (1 ) $ 72 $ 123 $ 145 $ (45 ) $ (60 ) $ (88 )
Obligation and Funded Status	Summarized information about the changes in plan assets and benefit obligations, the funded status and the amounts recorded at December 31 is as follows: Pension Benefits Other Postretirement Benefits U.S. International 2018 2017 2018 2017 2018 2017 Fair value of plan assets January 1 $ 10,896 $ 9,766 $ 9,339 $ 7,794 $ 1,114 $ 1,019 Actual return on plan assets (810 ) 1,723 (289 ) 677 (72 ) 161 Company contributions, net 378 58 167 226 6 (4 ) Effects of exchange rate changes — — (352 ) 843 — — Benefits paid (772 ) (651 ) (202 ) (198 ) (80 ) (62 ) Settlements (44 ) — (106 ) (17 ) — — Other — — 23 14 — — Fair value of plan assets December 31 $ 9,648 $ 10,896 $ 8,580 $ 9,339 $ 968 $ 1,114 Benefit obligation January 1 $ 11,904 $ 10,849 $ 9,483 $ 8,372 $ 1,922 $ 1,922 Service cost 326 312 238 252 57 57 Interest cost 432 454 178 172 69 81 Actuarial (gains) losses (1) (1,258 ) 881 (154 ) (7 ) (341 ) (87 ) Benefits paid (772 ) (651 ) (202 ) (198 ) (80 ) (62 ) Effects of exchange rate changes — — (387 ) 916 (6 ) 3 Plan amendments — — 10 (22 ) (9 ) — Curtailments 13 15 (2 ) (3 ) — — Termination benefits 19 44 2 4 3 8 Settlements (44 ) — (106 ) (17 ) — — Other — — 23 14 — — Benefit obligation December 31 $ 10,620 $ 11,904 $ 9,083 $ 9,483 $ 1,615 $ 1,922 Funded status December 31 $ (972 ) $ (1,008 ) $ (503 ) $ (144 ) $ (647 ) $ (808 ) Recognized as: Other assets $ — $ — $ 659 $ 828 $ — $ — Accrued and other current liabilities (47 ) (59 ) (14 ) (17 ) (10 ) (11 ) Other noncurrent liabilities (925 ) (949 ) (1,148 ) (955 ) (637 ) (797 ) (1) Actuarial (gains) losses in 2018 and 2017 primarily reflect changes in discount rates.
Schedule of Accumulated and Projected Benefit Obligations in Excess of Fair Value of Plan Assets [Table Text Block]	Information related to the funded status of selected pension plans at December 31 is as follows: U.S. International 2018 2017 2018 2017 Pension plans with a projected benefit obligation in excess of plan assets Projected benefit obligation $ 10,620 $ 11,904 $ 6,251 $ 3,323 Fair value of plan assets 9,648 10,896 5,089 2,352 Pension plans with an accumulated benefit obligation in excess of plan assets Accumulated benefit obligation $ 9,702 $ 676 $ 5,936 $ 2,120 Fair value of plan assets 8,966 — 5,071 1,346
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Summary of Changes in Fair Value of Company's Level 3 Pension Plan Assets	The table below provides a summary of the changes in fair value, including transfers in and/or out, of all financial assets measured at fair value using significant unobservable inputs (Level 3) for the Company’s pension plan assets: 2018 2017 Insurance Contracts Real Estate Other Total Insurance Contracts Real Estate Other Total U.S. Pension Plans Balance January 1 $ — $ — $ 15 $ 15 $ — $ — $ 18 $ 18 Actual return on plan assets: Relating to assets still held at December 31 — — (3 ) (3 ) — — (2 ) (2 ) Relating to assets sold during the year — — 4 4 — — 4 4 Purchases and sales, net — — (3 ) (3 ) — — (5 ) (5 ) Balance December 31 $ — $ — $ 13 $ 13 $ — $ — $ 15 $ 15 International Pension Plans Balance January 1 $ 470 $ 2 $ 1 $ 473 $ 412 $ 4 $ 1 $ 417 Actual return on plan assets: Relating to assets still held at December 31 (32 ) — — (32 ) 52 — — 52 Purchases and sales, net 380 (1 ) — 379 5 (2 ) — 3 Transfers into Level 3 (7 ) — — (7 ) 1 — — 1 Balance December 31 $ 811 $ 1 $ 1 $ 813 $ 470 $ 2 $ 1 $ 473
Summary of Expected Benefit Payments	Expected benefit payments are as follows: U.S. Pension Benefits International Pension Benefits Other Postretirement Benefits 2019 $ 638 $ 225 $ 91 2020 661 213 95 2021 680 221 98 2022 685 239 102 2023 709 249 105 2024 — 2028 3,805 1,349 577
Components of Other Comprehensive Income	The following amounts were reflected as components of OCI : Pension Plans Other Postretirement Benefit Plans U.S. International Years Ended December 31 2018 2017 2016 2018 2017 2016 2018 2017 2016 Net (loss) gain arising during the period $ (397 ) $ (19 ) $ (743 ) $ (505 ) $ 309 $ (380 ) $ 186 $ 170 $ (45 ) Prior service (cost) credit arising during the period (4 ) (13 ) (10 ) (10 ) 22 (2 ) 2 (31 ) (19 ) $ (401 ) $ (32 ) $ (753 ) $ (515 ) $ 331 $ (382 ) $ 188 $ 139 $ (64 ) Net loss amortization included in benefit cost $ 232 $ 180 $ 119 $ 84 $ 98 $ 87 $ 1 $ 1 $ 3 Prior service (credit) cost amortization included in benefit cost (50 ) (53 ) (55 ) (13 ) (11 ) (11 ) (84 ) (98 ) (106 ) $ 182 $ 127 $ 64 $ 71 $ 87 $ 76 $ (83 ) $ (97 ) $ (103 )
Summary of Weighted Average Assumptions Used in Determining Pension Plan and U.S. Pension and Other Postretirement Benefit Plan Information	The Company reassesses its benefit plan assumptions on a regular basis. The weighted average assumptions used in determining U.S. pension and other postretirement benefit plan and international pension plan information are as follows: U.S. Pension and Other Postretirement Benefit Plans International Pension Plans December 31 2018 2017 2016 2018 2017 2016 Net periodic benefit cost Discount rate 3.70 % 4.30 % 4.70 % 2.10 % 2.20 % 2.80 % Expected rate of return on plan assets 8.20 % 8.70 % 8.60 % 5.10 % 5.10 % 5.60 % Salary growth rate 4.30 % 4.30 % 4.30 % 2.90 % 2.90 % 2.90 % Benefit obligation Discount rate 4.40 % 3.70 % 4.30 % 2.20 % 2.10 % 2.20 % Salary growth rate 4.30 % 4.30 % 4.30 % 2.80 % 2.90 % 2.90 %
Summary of Health Care Cost Trend Rate Assumptions for Other Postretirement Benefit Plans	The health care cost trend rate assumptions for other postretirement benefit plans are as follows: December 31 2018 2017 Health care cost trend rate assumed for next year 7.0 % 7.2 % Rate to which the cost trend rate is assumed to decline 4.5 % 4.5 % Year that the trend rate reaches the ultimate trend rate 2032 2032
One Percentage Point Change in Health Care Cost Trend Rate	A one percentage point change in the health care cost trend rate would have had the following effects: One Percentage Point Increase Decrease Effect on total service and interest cost components $ 11 $ (9 ) Effect on benefit obligation 88 (74 )
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Schedule of Allocation of Plan Assets [Table Text Block]	The fair values of the Company’s pension plan assets at December 31 by asset category are as follows: Fair Value Measurements Using Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total 2018 2017 U.S. Pension Plans Assets Cash and cash equivalents $ 40 $ — $ — $ 40 $ 6 $ — $ — $ 6 Investment funds Developed markets equities 169 — — 169 390 — — 390 Emerging markets equities 121 — — 121 138 — — 138 Equity securities Developed markets 2,172 — — 2,172 2,743 — — 2,743 Fixed income securities Government and agency obligations — 1,509 — 1,509 — 757 — 757 Corporate obligations — 1,246 — 1,246 — 900 — 900 Mortgage and asset-backed securities — 262 — 262 — 240 — 240 Other investments — — 13 13 — — 15 15 Net assets in fair value hierarchy $ 2,502 $ 3,017 $ 13 $ 5,532 $ 3,277 $ 1,897 $ 15 $ 5,189 Investments measured at NAV (1) 4,116 5,707 Plan assets at fair value $ 9,648 $ 10,896 International Pension Plans Assets Cash and cash equivalents $ 50 $ 3 $ — $ 53 $ 54 $ 19 $ — $ 73 Investment funds Developed markets equities 461 3,071 — 3,532 562 3,326 — 3,888 Emerging markets equities 56 112 — 168 62 176 — 238 Government and agency obligations 372 2,082 — 2,454 249 2,095 — 2,344 Corporate obligations 4 7 — 11 5 329 — 334 Fixed income obligations 7 4 — 11 7 4 — 11 Real estate (2) — 1 1 2 — 1 2 3 Equity securities Developed markets 544 — — 544 660 — — 660 Fixed income securities Government and agency obligations 2 291 — 293 2 266 — 268 Corporate obligations 1 113 — 114 1 118 — 119 Mortgage and asset-backed securities — 55 — 55 — 55 — 55 Other investments Insurance contracts (3) — 66 811 877 — 67 470 537 Other — 4 1 5 — 6 1 7 Net assets in fair value hierarchy $ 1,497 $ 5,809 $ 813 $ 8,119 $ 1,602 $ 6,462 $ 473 $ 8,537 Investments measured at NAV (1) 461 802 Plan assets at fair value $ 8,580 $ 9,339 (1) Certain investments that were measured at net asset value (NAV) per share or its equivalent as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the fair value of plan assets at December 31, 2018 and 2017 . (2) The plans’ Level 3 investments in real estate funds are generally valued by market appraisals of the underlying investments in the funds. (3) The plans’ Level 3 investments in insurance contracts are generally valued using a crediting rate that approximates market returns and invest in underlying securities whose market values are unobservable and determined using pricing models, discounted cash flow methodologies, or similar techniques.
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Schedule of Allocation of Plan Assets [Table Text Block]	The fair values of the Company’s other postretirement benefit plan assets at December 31 by asset category are as follows: Fair Value Measurements Using Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total 2018 2017 Assets Cash and cash equivalents $ 78 $ — $ — $ 78 $ 97 $ — $ — $ 97 Investment funds Developed markets equities 16 — — 16 37 — — 37 Emerging markets equities 12 — — 12 13 — — 13 Government and agency obligations 1 — — 1 1 — — 1 Equity securities Developed markets 200 — — 200 256 — — 256 Fixed income securities Government and agency obligations — 141 — 141 — 71 — 71 Corporate obligations — 116 — 116 — 84 — 84 Mortgage and asset-backed securities — 24 — 24 — 23 — 23 Net assets in fair value hierarchy $ 307 $ 281 $ — $ 588 $ 404 $ 178 $ — $ 582 Investments measured at NAV (1) 380 532 Plan assets at fair value $ 968 $ 1,114 (1) Certain investments that were measured at net asset value (NAV) per share or its equivalent as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the fair value of plan assets at December 31, 2018 and 2017 .

Other (Income) Expense, Net (Ta

Other (Income) Expense, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Other Income and Expenses [Abstract]
Other (Income) Expense, Net	Other (income) expense, net, consisted of: Years Ended December 31 2018 2017 2016 Interest income $ (343 ) $ (385 ) $ (328 ) Interest expense 772 754 693 Exchange losses (gains) 145 (11 ) 174 Income on investments in equity securities, net (1) (324 ) (352 ) (43 ) Net periodic defined benefit plan (credit) cost other than service cost (512 ) (512 ) (531 ) Other, net (140 ) 6 224 $ (402 ) $ (500 ) $ 189 (1) Includes net realized and unrealized gains and losses on investments in equity securities either owned directly or through ownership interests in investment funds.

Taxes on Income (Tables)

Taxes on Income (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Reconciliation Between Effective Tax Rate and U.S. Statutory Rate	A reconciliation between the effective tax rate and the U.S. statutory rate is as follows: 2018 2017 2016 Amount Tax Rate Amount Tax Rate Amount Tax Rate U.S. statutory rate applied to income before taxes $ 1,827 21.0 % $ 2,282 35.0 % $ 1,631 35.0 % Differential arising from: Impact of the TCJA 289 3.3 2,625 40.3 — — Valuation allowances 269 3.1 632 9.7 (5 ) (0.1 ) Impact of purchase accounting adjustments, including amortization 267 3.1 713 10.9 623 13.4 State taxes 201 2.3 77 1.2 173 3.7 Restructuring 56 0.6 142 2.2 145 3.1 Foreign earnings (245 ) (2.8 ) (1,654 ) (25.4 ) (1,546 ) (33.2 ) R&D tax credit (96 ) (1.1 ) (71 ) (1.1 ) (58 ) (1.3 ) Tax settlements (22 ) (0.3 ) (356 ) (5.5 ) — — Other (1) (38 ) (0.4 ) (287 ) (4.4 ) (245 ) (5.2 ) $ 2,508 28.8 % $ 4,103 62.9 % $ 718 15.4 % (1) Other includes the tax effects of losses on foreign subsidiaries and miscellaneous items.
Income Before Taxes	Income before taxes consisted of: Years Ended December 31 2018 2017 2016 Domestic $ 3,717 $ 3,483 $ 518 Foreign 4,984 3,038 4,141 $ 8,701 $ 6,521 $ 4,659
Taxes on Income	Taxes on income consisted of: Years Ended December 31 2018 2017 2016 Current provision Federal $ 536 $ 5,585 $ 1,166 Foreign 2,281 1,229 916 State 200 (90 ) 157 3,017 6,724 2,239 Deferred provision Federal (402 ) (2,958 ) (1,255 ) Foreign (64 ) 75 (225 ) State (43 ) 262 (41 ) (509 ) (2,621 ) (1,521 ) $ 2,508 $ 4,103 $ 718
Deferred Income Taxes	Deferred income taxes at December 31 consisted of: 2018 2017 Assets Liabilities Assets Liabilities Product intangibles and licenses $ 720 $ 1,640 $ 307 $ 2,256 Inventory related 32 377 29 499 Accelerated depreciation — 582 28 642 Pensions and other postretirement benefits 565 151 498 192 Compensation related 291 — 314 — Unrecognized tax benefits 174 — 156 — Net operating losses and other tax credit carryforwards 715 — 654 — Other 621 66 909 52 Subtotal 3,118 2,816 2,895 3,641 Valuation allowance (1,348 ) (900 ) Total deferred taxes $ 1,770 $ 2,816 $ 1,995 $ 3,641 Net deferred income taxes $ 1,046 $ 1,646 Recognized as: Other assets $ 656 $ 573 Deferred income taxes $ 1,702 $ 2,219
Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: 2018 2017 2016 Balance January 1 $ 1,723 $ 3,494 $ 3,448 Additions related to current year positions 221 146 196 Additions related to prior year positions 142 520 75 Reductions for tax positions of prior years (1) (73 ) (1,038 ) (90 ) Settlements (1) (91 ) (1,388 ) (92 ) Lapse of statute of limitations (29 ) (11 ) (43 ) Balance December 31 $ 1,893 $ 1,723 $ 3,494 (1) Amounts reflect the settlements with the IRS as discussed below.

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Calculations of Earnings Per Share	The calculations of earnings per share (shares in millions) are as follows: Years Ended December 31 2018 2017 2016 Net income attributable to Merck & Co., Inc. $ 6,220 $ 2,394 $ 3,920 Average common shares outstanding 2,664 2,730 2,766 Common shares issuable (1) 15 18 21 Average common shares outstanding assuming dilution 2,679 2,748 2,787 Basic earnings per common share attributable to Merck & Co., Inc. common shareholders $ 2.34 $ 0.88 $ 1.42 Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders $ 2.32 $ 0.87 $ 1.41 (1) Issuable primarily under share-based compensation plans.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2018
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes in AOCI by Component	Changes in AOCI by component are as follows: Derivatives Investments Employee Benefit Plans Cumulative Translation Adjustment Accumulated Other Comprehensive Income (Loss) Balance January 1, 2016, net of taxes $ 404 $ 41 $ (2,407 ) $ (2,186 ) $ (4,148 ) Other comprehensive income (loss) before reclassification adjustments, pretax 210 (38 ) (1,199 ) (150 ) (1,177 ) Tax (72 ) 16 363 (19 ) 288 Other comprehensive income (loss) before reclassification adjustments, net of taxes 138 (22 ) (836 ) (169 ) (889 ) Reclassification adjustments, pretax (314 ) (1) (31 ) (2) 37 (3) — (308 ) Tax 110 9 — — 119 Reclassification adjustments, net of taxes (204 ) (22 ) 37 — (189 ) Other comprehensive income (loss), net of taxes (66 ) (44 ) (799 ) (169 ) (1,078 ) Balance December 31, 2016, net of taxes 338 (3 ) (3,206 ) (2,355 ) (5,226 ) Other comprehensive income (loss) before reclassification adjustments, pretax (561 ) 212 438 235 324 Tax 207 (35 ) (106 ) 166 232 Other comprehensive income (loss) before reclassification adjustments, net of taxes (354 ) 177 332 401 556 Reclassification adjustments, pretax (141 ) (1) (291 ) (2) 117 (3) — (315 ) Tax 49 56 (30 ) — 75 Reclassification adjustments, net of taxes (92 ) (235 ) 87 — (240 ) Other comprehensive income (loss), net of taxes (446 ) (58 ) 419 401 316 Balance December 31, 2017, net of taxes (108 ) (61 ) (2,787 ) (4) (1,954 ) (4,910 ) Other comprehensive income (loss) before reclassification adjustments, pretax 228 (108 ) (728 ) (84 ) (692 ) Tax (55 ) 1 169 (139 ) (24 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes 173 (107 ) (559 ) (223 ) (716 ) Reclassification adjustments, pretax 157 (1) 97 (2) 170 (3) — 424 Tax (33 ) — (36 ) — (69 ) Reclassification adjustments, net of taxes 124 97 134 — 355 Other comprehensive income (loss), net of taxes 297 (10 ) (425 ) (223 ) (361 ) Adoption of ASU 2018-02 (see Note 2) (23 ) 1 (344 ) 100 (266 ) Adoption of ASU 2016-01 (see Note 2) — (8 ) — — (8 ) Balance December 31, 2018, net of taxes $ 166 $ (78 ) $ (3,556 ) (4) $ (2,077 ) $ (5,545 ) (1) Relates to foreign currency cash flow hedges that were reclassified from AOCI to Sales . (2) Represents net realized (gains) losses on the sales of available-for-sale investments that were reclassified from AOCI to Other (income) expense, net . In 2017 and 2016, these amounts included both investments in debt and equity securities; however, as a result of the adoption of ASU 2016-01 (see Note 2), in 2018, these amounts relate only to investments in available-for-sale debt securities. (3) Includes net amortization of prior service cost and actuarial gains and losses included in net periodic benefit cost (see Note 14). (4) Includes pension plan net loss of $ 4.4 billion and $3.5 billion at December 31, 2018 and 2017 , respectively, and other postretirement benefit plan net (gain) loss of $(170) million and $(16) million at December 31, 2018 and 2017 , respectively, as well as pension plan prior service credit of $314 million and $326 million at December 31, 2018 and 2017 , respectively, and other postretirement benefit plan prior service credit of $375 million and $383 million at December 31, 2018 and 2017 , respectively.

Segment Reporting (Tables)

Segment Reporting (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Sales of Company's Products	Sales of the Company’s products were as follows: Years Ended December 31 2018 2017 2016 U.S. Int’l Total U.S. Int’l Total U.S. Int’l Total Pharmaceutical: Oncology Keytruda $ 4,150 $ 3,021 $ 7,171 $ 2,309 $ 1,500 $ 3,809 $ 792 $ 610 $ 1,402 Emend 312 210 522 342 213 556 356 193 549 Temodar 6 209 214 16 256 271 15 268 283 Alliance revenue - Lynparza 127 61 187 — 20 20 — — — Alliance revenue - Lenvima 95 54 149 — — — — — — Vaccines (1) Gardasil/Gardasil 9 1,873 1,279 3,151 1,565 743 2,308 1,780 393 2,173 ProQuad/M-M-R II/Varivax 1,430 368 1,798 1,374 303 1,676 1,362 279 1,640 Pneumovax 23 627 281 907 581 240 821 447 193 641 RotaTeq 496 232 728 481 204 686 482 169 652 Zostavax 22 195 217 422 246 668 518 168 685 Hospital Acute Care Bridion 386 531 917 239 465 704 77 405 482 Noxafil 353 389 742 309 327 636 284 312 595 Invanz 253 243 496 361 241 602 329 233 561 Cubicin 191 176 367 189 193 382 906 181 1,087 Cancidas 12 314 326 20 402 422 25 533 558 Primaxin 7 258 265 10 270 280 4 293 297 Immunology Simponi — 893 893 — 819 819 — 766 766 Remicade — 582 582 — 837 837 — 1,268 1,268 Neuroscience Belsomra 96 164 260 98 112 210 84 70 154 Virology Isentress/Isentress HD 513 627 1,140 565 639 1,204 721 666 1,387 Zepatier 8 447 455 771 888 1,660 488 67 555 Cardiovascular Zetia 45 813 857 352 992 1,344 1,588 972 2,560 Vytorin 10 487 497 124 627 751 473 668 1,141 Atozet — 347 347 — 225 225 1 146 146 Adempas — 329 329 — 300 300 — 169 169 Diabetes Januvia 1,969 1,718 3,686 2,153 1,584 3,737 2,286 1,622 3,908 Janumet 811 1,417 2,228 863 1,296 2,158 984 1,217 2,201 Women’s Health NuvaRing 722 180 902 564 197 761 576 202 777 Implanon/Nexplanon 495 208 703 496 191 686 420 186 606 Diversified Brands Singulair 20 688 708 40 692 732 40 874 915 Cozaar/Hyzaar 23 431 453 18 466 484 16 494 511 Nasonex 23 353 376 54 333 387 184 352 537 Arcoxia — 335 335 — 363 363 — 450 450 Follistim AQ 115 153 268 123 174 298 157 197 355 Dulera 186 28 214 261 26 287 412 24 436 Fosamax 4 205 209 6 235 241 5 279 284 Other pharmaceutical (2) 1,228 2,855 4,090 1,148 2,917 4,065 1,261 3,158 4,420 Total Pharmaceutical segment sales 16,608 21,081 37,689 15,854 19,536 35,390 17,073 18,077 35,151 Animal Health: Livestock 528 2,102 2,630 471 2,013 2,484 446 1,841 2,287 Companion Animals 710 872 1,582 619 772 1,391 543 648 1,191 Total Animal Health segment sales 1,238 2,974 4,212 1,090 2,785 3,875 989 2,489 3,478 Other segment sales (3) 248 2 250 396 1 397 385 — 385 Total segment sales 18,094 24,057 42,151 17,340 22,322 39,662 18,447 20,566 39,014 Other (4) 118 26 143 84 376 460 31 763 793 $ 18,212 $ 24,083 $ 42,294 $ 17,424 $ 22,698 $ 40,122 $ 18,478 $ 21,329 $ 39,807 U.S. plus international may not equal total due to rounding. (1) On December 31, 2016, Merck and Sanofi terminated their equally-owned joint venture, SPMSD, which marketed vaccines in most major European markets (see Note 9). Accordingly, vaccine sales in 2018 and 2017 include sales in the European markets that were previously part of SPMSD. Amounts for 2016 do not include sales of vaccines sold through SPMSD, the results of which are reflected in equity income from affiliates included in Other (income) expense, net . Amounts for 2016 do, however, include supply sales to SPMSD. (2) Other pharmaceutical primarily reflects sales of other human health pharmaceutical products, including products within the franchises not listed separately. (3) Represents the non-reportable segments of Healthcare Services and Alliances. (4) Other is primarily comprised of miscellaneous corporate revenues, including revenue hedging activities, as well as third-party manufacturing sales. Other in 2018, 2017 and 2016 also includes approximately $95 million , $85 million and $170 million , respectively, related to the sale of the marketing rights to certain products.
Consolidated Revenues by Geographic Area	Consolidated revenues by geographic area where derived are as follows: Years Ended December 31 2018 2017 2016 United States $ 18,212 $ 17,424 $ 18,478 Europe, Middle East and Africa 12,213 11,478 10,953 Japan 3,212 3,122 2,846 Asia Pacific (other than Japan and China) 2,909 2,751 2,483 Latin America 2,415 2,339 2,155 China 2,184 1,586 1,435 Other 1,149 1,422 1,457 $ 42,294 $ 40,122 $ 39,807
Reconciliation of Segment Profits to Income Before Taxes	A reconciliation of segment profits to Income before taxes is as follows: Years Ended December 31 2018 2017 2016 Segment profits: Pharmaceutical segment $ 24,292 $ 22,495 $ 22,141 Animal Health segment 1,659 1,552 1,357 Other segments 103 275 146 Total segment profits 26,054 24,322 23,644 Other profits 6 26 481 Unallocated: Interest income 343 385 328 Interest expense (772 ) (754 ) (693 ) Depreciation and amortization (1,334 ) (1,378 ) (1,585 ) Research and development (8,853 ) (9,481 ) (9,218 ) Amortization of purchase accounting adjustments (2,664 ) (3,056 ) (3,692 ) Restructuring costs (632 ) (776 ) (651 ) Charge related to termination of collaboration agreement with Samsung (423 ) — — Loss on extinguishment of debt — (191 ) — Gain on sale of certain migraine clinical development programs — — 100 Charge related to the settlement of worldwide Keytruda patent litigation — — (625 ) Other unallocated, net (3,024 ) (2,576 ) (3,430 ) $ 8,701 $ 6,521 $ 4,659
Equity Income from Affiliates and Depreciation and Amortization Included in Segment Profits	Equity (income) loss from affiliates and depreciation and amortization included in segment profits is as follows: Pharmaceutical Animal Health All Other Total Year Ended December 31, 2018 Included in segment profits: Equity (income) loss from affiliates $ 4 $ — $ — $ 4 Depreciation and amortization 243 82 10 335 Year Ended December 31, 2017 Included in segment profits: Equity (income) loss from affiliates $ 7 $ — $ — $ 7 Depreciation and amortization 125 75 12 212 Year Ended December 31, 2016 Included in segment profits: Equity (income) loss from affiliates $ (105 ) $ — $ — $ (105 ) Depreciation and amortization 160 10 13 183
Property, Plant and Equipment, Net by Geographic Area	Property, plant and equipment, net, by geographic area where located is as follows: December 31 2018 2017 2016 United States $ 8,306 $ 8,070 $ 8,114 Europe, Middle East and Africa 3,706 3,151 2,732 Asia Pacific (other than Japan and China) 684 632 623 Latin America 264 271 234 China 167 150 152 Japan 159 158 164 Other 5 7 7 $ 13,291 $ 12,439 $ 12,026

Nature of Operations (Details)

Nature of Operations (Details)	12 Months Ended
	Dec. 31, 2018segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	4

Summary of Accounting Policie_3

Summary of Accounting Policies - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Jan. 01, 2018
Summary Of Significant Accounting Policies [Line Items]
Product return period and expiration	12 months
Customer discounts	$ 10,700	$ 10,700	$ 9,700
Accrual for chargebacks reflected as direct reduction to accounts receivable	245	198
Accrual for rebates included in accrued and other current liabilities	2,400	2,400
Depreciation	1,400	1,500	1,600
Advertising and promotion costs	2,100	2,200	2,100
Decrease in deferred income taxes	(1,702)	(2,219)
Accumulated other comprehensive loss	5,545	4,910
Net periodic defined benefit plan (credit) cost other than service cost	(512)	(512)	$ (531)
ASU 2016-01 (Financial Instruments)
Summary Of Significant Accounting Policies [Line Items]
Increase (decrease) in retained earnings	8
Accumulated other comprehensive loss					$ 8
ASU 2016-16 (Intra-Entity Transfers Other than Inventory)
Summary Of Significant Accounting Policies [Line Items]
Increase (decrease) in retained earnings	54
Decrease in deferred income taxes	54				54
Accounting Standards Update 2017-12
Summary Of Significant Accounting Policies [Line Items]
Increase (decrease) in retained earnings	(11)
Accounting Standard Update 2018-02
Summary Of Significant Accounting Policies [Line Items]
Accumulated other comprehensive loss					$ 266
Enterprise wide resource planning system
Summary Of Significant Accounting Policies [Line Items]
Unamortized capitalized software costs	439	$ 449
Difference between Revenue Guidance in Effect before and after Topic 606 | ASU 2014-09 (Revenue)
Summary Of Significant Accounting Policies [Line Items]
Increase (decrease) in retained earnings	$ 5
Minimum
Summary Of Significant Accounting Policies [Line Items]
Product return period	3 months
Estimated useful life of intangible assets	2 years
Minimum | Enterprise wide resource planning system
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	6 years
Minimum | Capitalized Software
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	3 years
Minimum | Buildings
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property, plant and equipment	25 years
Minimum | Machinery, equipment and office furnishings
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property, plant and equipment	3 years
Minimum | United States | Pharmaceutical segment
Summary Of Significant Accounting Policies [Line Items]
Payment terms	36 days
Minimum | United States | Animal Health
Summary Of Significant Accounting Policies [Line Items]
Payment terms	30 days
Minimum | Outside of the United States
Summary Of Significant Accounting Policies [Line Items]
Payment terms	30 days
Maximum
Summary Of Significant Accounting Policies [Line Items]
Product return period	6 months
Estimated useful life of intangible assets	20 years
Maximum | Enterprise wide resource planning system
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	10 years
Maximum | Capitalized Software
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	5 years
Maximum | Buildings
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property, plant and equipment	45 years
Maximum | Machinery, equipment and office furnishings
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property, plant and equipment	15 years
Maximum | United States | Animal Health
Summary Of Significant Accounting Policies [Line Items]
Payment terms	90 days
Maximum | Outside of the United States
Summary Of Significant Accounting Policies [Line Items]
Payment terms	90 days
Subsequent Event | Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Operating lease, right-of-use assets				$ 1,000
Operating lease, liability				$ 1,000

Summary of Accounting Policie_4

Summary of Accounting Policies - Effects of Adopting ASC 606 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	$ 42,294	$ 40,122	$ 39,807
Cost of sales	13,509	12,912	14,030
Income before taxes	8,701	6,521	4,659
Taxes on Income	2,508	4,103	718
Net Income Attributable to Merck & Co., Inc.	6,220	2,394	$ 3,920
Assets
Accounts receivable	7,071	6,873
Inventories	5,440	5,096
Liabilities
Accrued and other current liabilities	10,151	10,427
Income taxes payable	1,971	708
Equity
Retained earnings	42,579	$ 41,350
Amounts Without Adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	42,292
Cost of sales	13,503
Income before taxes	8,705
Taxes on Income	2,509
Net Income Attributable to Merck & Co., Inc.	6,223
Assets
Accounts receivable	7,058
Inventories	5,447
Liabilities
Accrued and other current liabilities	10,148
Income taxes payable	1,970
Equity
Retained earnings	42,577
ASU 2014-09 (Revenue) | Effects of Adopting ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	(2)
Cost of sales	(6)
Income before taxes	4
Taxes on Income	1
Net Income Attributable to Merck & Co., Inc.	3
Assets
Accounts receivable	(13)			$ 5
Inventories	7
Liabilities
Accrued and other current liabilities	(3)
Income taxes payable	(1)
Equity
Retained earnings	$ (2)			$ 5

Summary of Accounting Policie_5

Summary of Accounting Policies - Impact of Adopting New Accounting Standards (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable	$ 7,071		$ 6,873
Liabilities
Income taxes payable	1,971		708
Debt	5,308		3,057
Deferred Income Taxes	1,702		2,219
Equity
Retained earnings	42,579		41,350
Accumulated other comprehensive loss	(5,545)		$ (4,910)
ASU 2016-01 (Financial Instruments)
Equity
Retained earnings		$ 8
Accumulated other comprehensive loss		(8)
ASU 2016-16 (Intra-Entity Transfers Other than Inventory)
Liabilities
Deferred Income Taxes	(54)	(54)
Equity
Retained earnings		54
ASU 2017-12 (Derivatives and Hedging)
Liabilities
Income taxes payable		(3)
Debt		14
Equity
Retained earnings		(11)
ASU 2018-02 (Reclassification of Certain Tax Effects)
Equity
Retained earnings		266
Accumulated other comprehensive loss		(266)
Adjustments for New Accounting Pronouncement
Assets
Accounts receivable		5
Liabilities
Income taxes payable		(3)
Debt		14
Deferred Income Taxes		(54)
Equity
Retained earnings		322
Accumulated other comprehensive loss		(274)
Effects of Adopting ASC 606 | ASU 2014-09 (Revenue)
Assets
Accounts receivable	(13)	5
Liabilities
Income taxes payable	(1)
Equity
Retained earnings	$ (2)	$ 5

Acquisitions, Divestitures, R_2

Acquisitions, Divestitures, Research Collaborations and License Agreements - Acquisitions Narrative (Detail) € in Millions, $ in Millions	1 Months Ended								3 Months Ended			12 Months Ended
	Jun. 30, 2018AUD ($)	Jun. 30, 2018USD ($)	Oct. 31, 2017USD ($)	Oct. 31, 2017EUR (€)	Mar. 31, 2017USD ($)	Jul. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Jan. 31, 2016USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2019EUR (€)	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2019EUR (€)
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Research and development												$ 9,752,000,000	$ 10,339,000,000	$ 10,261,000,000
Goodwill											$ 18,284,000,000	18,253,000,000	18,284,000,000	18,162,000,000
Contingent consideration											$ 935,000,000	788,000,000	935,000,000	$ 891,000,000
Payments of contingent consideration												244,000,000	$ 100,000,000
Measurement Input, Discount Rate
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Intangible asset, measurement input														0.115
Viralytics
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Cash paid for acquisition of business	$ 502	$ 378,000,000
Other net assets		$ 34,000,000
Research and development												344,000,000
Rigontec
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Cash paid for acquisition of business			$ 140,000,000	€ 119
Potential future milestone payments, maximum | €				349
Potential future milestone payment, research milestones and regulatory approvals | €				184
Potential future milestone payment, commercial targets | €				€ 165
Vallee SA
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Cash paid for acquisition of business					$ 358,000,000
Other net assets					$ 32,000,000
Voting rights acquired (as percent)					93.50%						4.50%		4.50%
Escrow deposit					$ 176,000,000
Identifiable intangible assets					297,000,000
Deferred tax liabilities					102,000,000
Noncontrolling interest					25,000,000
Contingent liabilities					37,000,000
Indemnification assets					37,000,000
Goodwill					$ 156,000,000
Estimated useful life of intangible assets, acquired					15 years
Payments to acquire additional interest											$ 18,000,000
Vallee SA | Measurement Input, Discount Rate
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Intangible asset, measurement input					0.155
Afferent Pharmaceuticals
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Cash paid for acquisition of business						$ 487,000,000
Consideration transferred in business combination						510,000,000
Other net assets						29,000,000
Potential future milestone payments, maximum						750,000,000
Deferred tax liabilities						258,000,000
Goodwill						130,000,000
Contingent consideration						223,000,000
In-process research and development (IPR&D)						$ 832,000,000
Payments of contingent consideration												$ 175,000,000
Afferent Pharmaceuticals | Measurement Input, Discount Rate
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Intangible asset, measurement input						0.115
Moderna Therapeutics
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Upfront and milestone payments							$ 200,000,000
IOmet Pharma Ltd
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Cash paid for acquisition of business								$ 150,000,000
Potential future milestone payments, maximum								250,000,000
Goodwill								57,000,000
Contingent consideration								94,000,000
In-process research and development (IPR&D)								155,000,000
Payments of contingent consideration													$ 100,000,000
Deferred tax assets								$ 32,000,000
IOmet Pharma Ltd | Measurement Input, Discount Rate
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Intangible asset, measurement input								0.105
Forecast | Antelliq
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Cash paid for acquisition of business									$ 2,400,000,000	€ 2,100
Debt assumed									$ 1,300,000,000						€ 1,100

Acquisitions, Divestitures, R_3

Acquisitions, Divestitures, Research Collaborations and License Agreements - Divestitures Narrative (Detail) - Samsung $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Acquisitions Divestitures Research Collaborations and License Agreements Transactions [Line Items]
Gain (loss) on contract termination	$ (423)
Contract termination fee	155
Fixed asset abandonment costs related to contract termination	137
Inventory write-off relate to contract termination	122
Other contract termination costs	$ 9

Collaborative Arrangements - Na

Collaborative Arrangements - Narrative (Details) $ in Millions	1 Months Ended				12 Months Ended						35 Months Ended
	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jul. 31, 2017USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)payment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jan. 31, 2021USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development								$ 9,752	$ 10,339	$ 10,261
Noncurrent liabilities			$ 11,117					12,041	11,117
Amortization expense for intangible assets								2,900	3,200	3,800
Estimated aggregate amortization expense, 2019								1,500
Estimated aggregate amortization expense, 2020								1,200
Estimated aggregate amortization expense, 2021								1,100
Estimated aggregate amortization expense, 2022								1,100
Estimated aggregate amortization expense, 2023								1,100
Capitalized Licenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amortization expense for intangible assets								186	39	$ 30
Estimated aggregate amortization expense, 2019								196
Estimated aggregate amortization expense, 2020								193
Estimated aggregate amortization expense, 2021								191
Estimated aggregate amortization expense, 2022								187
Estimated aggregate amortization expense, 2023								181
Lynparza | Other Assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Intangible assets								743
Lenvima | Other Assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Intangible assets								479
Adempas | Other Intangible Assets, Net
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Intangible assets								1,000
AstraZeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments				$ 1,600
Payments to acquire intangible assets			$ 250	$ 750				400
Research and development									$ 2,350
AstraZeneca | Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement								3,400
AstraZeneca | Regulatory Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement								1,760
AstraZeneca | Lynparza
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amortization expense for intangible assets								$ 58
AstraZeneca | Lynparza | Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of milestone payments | payment								3
Probable future contingent payments collaborative arrangement								$ 600
Liabilities								600
Milestone payments made to collaborative partner								150
AstraZeneca | Lynparza | Prior Year Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments made to collaborative partner								100
AstraZeneca | Lynparza | Regulatory Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments made to collaborative partner								140
AstraZeneca | Forecast
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payments to acquire intangible assets							$ 100
Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments		$ 750
Research and development								1,400
Eisai | Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement		3,970						3,710
Eisai | Regulatory Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement		$ 385						$ 135
Eisai | Lenvima | Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of milestone payments | payment								3
Probable future contingent payments collaborative arrangement								$ 268
Liabilities								268
Intangible assets								268
Amortization expense for intangible assets								24
Eisai | Lenvima | Regulatory Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments made to collaborative partner								250
Eisai | Forecast
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payments to acquire intangible assets	$ 325				$ 125	$ 200					$ 650
Bayer AG | Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement								400
Bayer AG | Adempas
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amortization expense for intangible assets								106
Bayer AG | Adempas | Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Probable future contingent payments collaborative arrangement								375
Noncurrent liabilities								375
Milestone payments made to collaborative partner								$ 350

Collaborative Arrangements - Sc

Collaborative Arrangements - Schedule of Collaborative Arrangement Transactions (Details) - Collaborative Arrangement - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AstraZeneca | Other current assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receivables from counterparty	$ 52	$ 12
AstraZeneca | Accrued and other current liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	405	543
AstraZeneca | Other noncurrent liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	250	100
AstraZeneca | Total sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total sales	187	20
AstraZeneca | Cost of sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	93	4
AstraZeneca | Selling, general and administrative
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	48	1
AstraZeneca | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	152	2,419
Eisai | Other current assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receivables from counterparty	71
Eisai | Accrued and other current liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	375
Eisai | Other noncurrent liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	543
Eisai | Total sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total sales	149
Eisai | Cost of sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	39
Eisai | Selling, general and administrative
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	13
Eisai | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	1,489
Bayer AG | Other current assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receivables from counterparty	32	33
Bayer AG | Accrued and other current liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	0	350
Bayer AG | Other noncurrent liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	375	0
Bayer AG | Total sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales recorded by Merck	190	149	$ 88
Merck’s profit share of sales in marketing territories	139	151	81
Total sales	329	300	169
Bayer AG | Cost of sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	216	99	133
Bayer AG | Selling, general and administrative
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	35	27	26
Bayer AG | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	$ 127	$ 101	$ 82

Restructuring - Narrative (Deta

Restructuring - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)position	Dec. 31, 2017USD ($)position	Dec. 31, 2016USD ($)position
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 658	$ 927	$ 1,069
Cumulative restructuring costs incurred to date since program inception	$ 14,100
Number of positions elimination since inception of program | position	45,510
Percentage estimate of cumulative pretax costs that will result in cash outlays (primarily from employee separation expense) (as percent)	66.67%
Percentage estimate of cumulative pretax costs that will be non-cash (primarily from accelerated depreciation of facilities) (as percent)	33.33%
Number of positions eliminated | position	2,160	2,450	2,625
Asset abandonment, shut-down and other related costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 141	$ 267	$ 409
Facility Closing
Restructuring Cost and Reserve [Line Items]
Pretax losses resulting from sales of facilities and related assets			$ 151

Restructuring - Charges Related

Restructuring - Charges Related to Restructuring Program Activities by Type of Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 658	$ 927	$ 1,069
Cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring costs	21	138	181
Selling, general and administrative
Restructuring Cost and Reserve [Line Items]
Restructuring costs	3	2	95
Research and development
Restructuring Cost and Reserve [Line Items]
Restructuring costs	2	11	142
Restructuring costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs	632	776	651
Separation Costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs	473	552	216
Separation Costs | Cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0	0	0
Separation Costs | Selling, general and administrative
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0	0	0
Separation Costs | Research and development
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0	0	0
Separation Costs | Restructuring costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs	473	552	216
Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Restructuring costs	(1)	60	227
Accelerated Depreciation | Cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring costs	10	52	77
Accelerated Depreciation | Selling, general and administrative
Restructuring Cost and Reserve [Line Items]
Restructuring costs	2	2	8
Accelerated Depreciation | Research and development
Restructuring Cost and Reserve [Line Items]
Restructuring costs	(13)	6	142
Accelerated Depreciation | Restructuring costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0	0	0
Other
Restructuring Cost and Reserve [Line Items]
Restructuring costs	186	315	626
Other | Cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring costs	11	86	104
Other | Selling, general and administrative
Restructuring Cost and Reserve [Line Items]
Restructuring costs	1	0	87
Other | Research and development
Restructuring Cost and Reserve [Line Items]
Restructuring costs	15	5	0
Other | Restructuring costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 159	$ 224	$ 435

Restructuring - Charges and Spe

Restructuring - Charges and Spending Relating to Restructuring Activities by Program (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 747	$ 541
Expenses	658	927	$ 1,069
(Payments) receipts, net	(887)	(722)
Non-cash activity	16	1
Restructuring reserve, ending balance	534	747	541
Separation Costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	619	395
Expenses	473	552	216
(Payments) receipts, net	(649)	(328)
Non-cash activity	0	0
Restructuring reserve, ending balance	443	619	395
Accelerated Depreciation
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0	0
Expenses	(1)	60	227
(Payments) receipts, net	0	0
Non-cash activity	1	(60)
Restructuring reserve, ending balance	0	0	0
Other
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	128	146
Expenses	186	315	626
(Payments) receipts, net	(238)	(394)
Non-cash activity	15	61
Restructuring reserve, ending balance	$ 91	$ 128	$ 146

Financial Instruments - Narrati

Financial Instruments - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)interest_rate_swap	Dec. 31, 2017USD ($)	May 31, 2018USD ($)interest_rate_swap
Derivative [Line Items]
Number of interest rate swaps held | interest_rate_swap	19
Notional amount of derivative	$ 29,742,000,000	$ 25,595,000,000
Pre tax net unrealized gain (loss) on derivatives maturing within next 12 months estimated to be reclassified from AOCI to sales	186,000,000
Equity investments without readily determinable fair values	568,000,000
Unrealized gains based on favorable observable price changes	167,000,000
Unrealized loss related to unfavorable observable price changes	26,000,000
Available-for-sale debt securities included in Short-term investments	894,000,000
Available-for-sale debt securities maturing within five years	5,800,000,000
Cash and cash equivalents	7,965,000,000	6,092,000,000
Payments of contingent consideration	244,000,000	100,000,000
Fair value of loans payable and long-term debt, including current portion	25,600,000,000	25,600,000,000
Carrying value of loans payable and long-term debt, including current portion	25,100,000,000	24,400,000,000
Cash collateral received from counterparties	$ 107,000,000	3,000,000
Customer Concentration Risk | Accounts Receivable | McKesson Corporation, AmerisourceBergen Corporation and Cardinal Health, Inc. [Member]
Derivative [Line Items]
Percentage of accounts receivable represented by customers with largest balances (as percent)	40.00%
Afferent Pharmaceuticals
Derivative [Line Items]
Payments of contingent consideration	$ 175,000,000
Significant Other Observable Inputs (Level 2)
Derivative [Line Items]
Cash and cash equivalents	8,000,000,000
Cash equivalents	$ 7,200,000,000
1.30% notes due 2018 | Interest Rate Swap
Derivative [Line Items]
Number of interest rate swaps held | interest_rate_swap			4
Notional amount of derivative			$ 1,000,000,000
Face amount of debt			$ 1,000,000,000
Fixed-rate notes, stated interest rate (as percent)			1.30%
5.00% notes due 2019 | Interest Rate Swap
Derivative [Line Items]
Number of interest rate swaps held | interest_rate_swap	3
Notional amount of derivative	$ 550,000,000
Face amount of debt	$ 1,250,000,000
Fixed-rate notes, stated interest rate (as percent)	5.00%
Derivatives Designated as Hedging Instruments
Derivative [Line Items]
Notional amount of derivative	$ 14,390,000,000	14,386,000,000
Derivatives Not Designated as Hedging Instruments
Derivative [Line Items]
Notional amount of derivative	$ 15,352,000,000	$ 11,209,000,000
Maximum | Derivatives Designated as Hedging Instruments
Derivative [Line Items]
Maximum planning cycle of third-party sales hedges (no more than)	2 years
Maximum | Derivatives Not Designated as Hedging Instruments
Derivative [Line Items]
Maximum planning cycle of third-party sales hedges (no more than)	1 year

Financial Instruments - Effect

Financial Instruments - Effect of Net Investment Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Foreign exchange contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income	$ (18)	$ 0	$ 2
Foreign exchange contracts | Other (income) expense, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing	(11)	0	(1)
Euro-denominated notes
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income	(183)	520	(193)
Euro-denominated notes | Other (income) expense, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing	$ 0	$ 0	$ 0

Financial Instruments - Informa

Financial Instruments - Information About Interest Rate Swaps (Details)	Dec. 31, 2018USD ($)interest_rate_swap	Dec. 31, 2017USD ($)
Derivative [Line Items]
Number of Interest Rate Swaps Held | interest_rate_swap	19
U.S. Dollar Notional	$ 29,742,000,000	$ 25,595,000,000
1.85% notes due 2020 | Interest Rate Swap
Derivative [Line Items]
Par Value of Debt	$ 1,250,000,000
Number of Interest Rate Swaps Held | interest_rate_swap	5
U.S. Dollar Notional	$ 1,250,000,000
Fixed-rate notes, stated interest rate (as percent)	1.85%
3.875% notes due 2021 | Interest Rate Swap
Derivative [Line Items]
Par Value of Debt	$ 1,150,000,000
Number of Interest Rate Swaps Held | interest_rate_swap	5
U.S. Dollar Notional	$ 1,150,000,000
Fixed-rate notes, stated interest rate (as percent)	3.875%
2.40% notes due 2022 | Interest Rate Swap
Derivative [Line Items]
Par Value of Debt	$ 1,000,000,000
Number of Interest Rate Swaps Held | interest_rate_swap	4
U.S. Dollar Notional	$ 1,000,000,000
Fixed-rate notes, stated interest rate (as percent)	2.40%
2.35% notes due 2022 | Interest Rate Swap
Derivative [Line Items]
Par Value of Debt	$ 1,250,000,000
Number of Interest Rate Swaps Held | interest_rate_swap	5
U.S. Dollar Notional	$ 1,250,000,000
Fixed-rate notes, stated interest rate (as percent)	2.35%

Financial Instruments - Fair Va

Financial Instruments - Fair Value of Hedges (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Hedging adjustment gains related to discontinued hedging relationships		$ 11
Loans payable and current portion of long-term debt
Derivative [Line Items]
Carrying Amount of Hedged Liabilities	$ 0	983
Cumulative Amount of Fair Value Hedging Adjustment Increase (Decrease) Included in the Carrying Amount	0	(17)
Long-Term Debt
Derivative [Line Items]
Carrying Amount of Hedged Liabilities	4,560	5,146
Cumulative Amount of Fair Value Hedging Adjustment Increase (Decrease) Included in the Carrying Amount	$ (82)	$ (41)

Financial Instruments - Fair _2

Financial Instruments - Fair Value of Derivatives Segregated Between Those Derivatives That are Designated as Hedging Instruments and Those That are Not Designated as Hedging Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	$ 454	$ 130
Fair Value of Derivative, Liability	160	217
U.S. Dollar Notional	29,742	25,595
Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	338	91
Fair Value of Derivative, Liability	89	127
U.S. Dollar Notional	14,390	14,386
Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	116	39
Fair Value of Derivative, Liability	71	90
U.S. Dollar Notional	15,352	11,209
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	0	2
U.S. Dollar Notional	0	550
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Accrued and other current liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	0	3
U.S. Dollar Notional	0	1,000
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	81	52
U.S. Dollar Notional	4,650	4,650
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	75	38
Fair Value of Derivative, Liability
U.S. Dollar Notional	2,655	1,936
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other current assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	263	51
U.S. Dollar Notional	6,222	4,216
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Accrued and other current liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	7	71
U.S. Dollar Notional	774	2,014
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	1	1
U.S. Dollar Notional	89	20
Foreign exchange contracts | Derivatives Not Designated as Hedging Instruments | Other current assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	116	39
U.S. Dollar Notional	5,430	3,778
Foreign exchange contracts | Derivatives Not Designated as Hedging Instruments | Accrued and other current liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	71	90
U.S. Dollar Notional	$ 9,922	$ 7,431

Financial Instruments - Infor_2

Financial Instruments - Information on Derivative Positions Subject to Master Netting Arrangements as if they were Presented on a Net Basis (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross amounts recognized in the consolidated balance sheet, Asset	$ 454	$ 130
Gross amount subject to offset in master netting arrangements not offset in the consolidated balance sheet, Asset	(121)	(94)
Cash collateral received, Asset	(107)	(3)
Net amounts, Asset	226	33
Gross amounts recognized in the consolidated balance sheet, Liability	160	217
Gross amount subject to offset in master netting arrangements not offset in the consolidated balance sheet, Liability	(121)	(94)
Cash collateral received, Liability	0	0
Net amounts, Liability	$ 39	$ 123

Financial Instruments - Locatio

Financial Instruments - Location and Pretax (Gains) or Loss Amounts for Derivatives (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Sales	$ 42,294	$ 40,122	$ 39,807
Other (income) expense, net	(402)	(500)	189
Other comprehensive income (loss)	(361)	316	(1,078)
Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in OCI on derivatives	228	(562)	210
(Decrease) increase in Sales as a result of AOCI reclassifications	160	(138)	(311)
Other (income) expense, net | Interest rate swap contracts
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items	(27)	(48)	(29)
Derivatives designated as hedging instruments	50	12	(35)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Sales	$ (160)	$ 138	$ 311

Financial Instruments - Effects

Financial Instruments - Effects of Derivatives Not Designated as Hedging Instruments (Details) - Foreign exchange contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other (income) expense, net
Derivative [Line Items]
Amount of Derivative Pretax (Gain) Loss Recognized in Income	$ 260	$ (110)	$ (132)
Sales
Derivative [Line Items]
Amount of Derivative Pretax (Gain) Loss Recognized in Income	$ 8	$ 3	$ 0

Financial Instruments - Infor_3

Financial Instruments - Information on Debt and Equity Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	$ 7,261	$ 14,908
Publicly traded equity securities, fair value	456
Publicly traded equity securities, fair value		275
Total debt and publicly traded equity securities, fair value	7,717
Total debt and publicly traded equity securities, fair value		15,183
Debt securities, amortized cost	7,340	14,976
Publicly traded equity securities, amortized cost		265
Total debt and publicly traded equity securities, amortized cost		15,241
Debt securities, gross unrealized gains	6	11
Publicly traded equity securities, gross unrealized gains		16
Total debt and publicly traded equity securities, gross unrealized gains		27
Debt securities, gross unrealized losses	(85)	(79)
Publicly traded equity securities, gross unrealized losses		(6)
Total debt and publicly traded equity securities, gross unrealized losses		(85)
Unrealized net gains	35
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	0	159
Debt securities, amortized cost	0	159
Debt securities, gross unrealized gains	0	0
Debt securities, gross unrealized losses	0	0
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	4,920	9,806
Debt securities, amortized cost	4,985	9,837
Debt securities, gross unrealized gains	3	9
Debt securities, gross unrealized losses	(68)	(40)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	1,275	1,542
Debt securities, amortized cost	1,285	1,548
Debt securities, gross unrealized gains	1	1
Debt securities, gross unrealized losses	(11)	(7)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	892	2,042
Debt securities, amortized cost	895	2,059
Debt securities, gross unrealized gains	2	0
Debt securities, gross unrealized losses	(5)	(17)
Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	166	733
Debt securities, amortized cost	167	739
Debt securities, gross unrealized gains	0	0
Debt securities, gross unrealized losses	(1)	(6)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	8	626
Debt securities, amortized cost	8	634
Debt securities, gross unrealized gains	0	1
Debt securities, gross unrealized losses	$ 0	$ (9)

Financial Instruments - Financi

Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Investments, debt securities	$ 7,261	$ 14,908
Publicly traded equity securities	456
Derivative assets	454	130
Liabilities
Contingent consideration	788	935	$ 891
Derivative liabilities	160	217
Commercial paper
Assets
Investments, debt securities	0	159
Corporate notes and bonds
Assets
Investments, debt securities	4,920	9,806
Asset-backed securities
Assets
Investments, debt securities	$ 1,275	1,542
Liabilities
Primary weighted-average lives of investment collateral (or less)	5 years
U.S. government and agency securities
Assets
Investments, debt securities	$ 892	2,042
Foreign government bonds
Assets
Investments, debt securities	166	733
Mortgage-backed securities
Assets
Investments, debt securities	8	626
Fair Value, Measurements, Recurring
Assets
Investments	7,132	14,531
Other assets	585	652
Derivative assets	454	130
Total assets	8,171	15,313
Liabilities
Contingent consideration	788	935
Derivative liabilities	160	217
Total liabilities	948	1,152
Fair Value, Measurements, Recurring | Interest rate swap contracts
Assets
Derivative assets	0	2
Liabilities
Derivative liabilities	81	55
Fair Value, Measurements, Recurring | Foreign exchange contracts
Assets
Derivative assets	241	48
Liabilities
Derivative liabilities	74	162
Fair Value, Measurements, Recurring | Purchased currency options
Assets
Derivative assets	213	80
Liabilities
Derivative liabilities	5	0
Fair Value, Measurements, Recurring | Commercial paper
Assets
Investments, debt securities	0	159
Fair Value, Measurements, Recurring | Corporate notes and bonds
Assets
Investments, debt securities	4,835	9,678
Other assets	85	128
Fair Value, Measurements, Recurring | Asset-backed securities
Assets
Investments, debt securities	1,253	1,476
Other assets	22	66
Fair Value, Measurements, Recurring | U.S. government and agency securities
Assets
Investments, debt securities	731	1,835
Other assets	161	207
Fair Value, Measurements, Recurring | Foreign government bonds
Assets
Investments, debt securities	166	732
Other assets	0	1
Fair Value, Measurements, Recurring | Mortgage-backed securities
Assets
Investments, debt securities	0	547
Other assets	8	79
Fair Value, Measurements, Recurring | Publicly traded equity securities
Assets
Publicly traded equity securities	147	104
Other assets	309	171
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Investments	147	172
Other assets	364	171
Derivative assets	0	0
Total assets	511	343
Liabilities
Contingent consideration	0	0
Derivative liabilities	0	0
Total liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Interest rate swap contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Foreign exchange contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Purchased currency options
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Commercial paper
Assets
Investments, debt securities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate notes and bonds
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Asset-backed securities
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | U.S. government and agency securities
Assets
Investments, debt securities	0	68
Other assets	55	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Foreign government bonds
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Mortgage-backed securities
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Publicly traded equity securities
Assets
Publicly traded equity securities	147	104
Other assets	309	171
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets
Investments	6,985	14,359
Other assets	221	481
Derivative assets	454	130
Total assets	7,660	14,970
Liabilities
Contingent consideration	0	0
Derivative liabilities	160	217
Total liabilities	160	217
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swap contracts
Assets
Derivative assets	0	2
Liabilities
Derivative liabilities	81	55
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign exchange contracts
Assets
Derivative assets	241	48
Liabilities
Derivative liabilities	74	162
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Purchased currency options
Assets
Derivative assets	213	80
Liabilities
Derivative liabilities	5	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial paper
Assets
Investments, debt securities	0	159
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate notes and bonds
Assets
Investments, debt securities	4,835	9,678
Other assets	85	128
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Asset-backed securities
Assets
Investments, debt securities	1,253	1,476
Other assets	22	66
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. government and agency securities
Assets
Investments, debt securities	731	1,767
Other assets	106	207
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign government bonds
Assets
Investments, debt securities	166	732
Other assets	0	1
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Assets
Investments, debt securities	0	547
Other assets	8	79
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Publicly traded equity securities
Assets
Publicly traded equity securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets
Investments	0	0
Other assets	0	0
Derivative assets	0	0
Total assets	0	0
Liabilities
Contingent consideration	788	935
Derivative liabilities	0	0
Total liabilities	788	935
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Interest rate swap contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign exchange contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Purchased currency options
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Commercial paper
Assets
Investments, debt securities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate notes and bonds
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Asset-backed securities
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. government and agency securities
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign government bonds
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Mortgage-backed securities
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Publicly traded equity securities
Assets
Publicly traded equity securities	0	0
Other assets	$ 0	$ 0

Financial Instruments - Summari

Financial Instruments - Summarized Information About Changes in Liabilities for Contingent Consideration (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration	$ 935	$ 891
Changes in estimated fair value	89	141
Additions	8	3
Payments	(244)	(100)
Contingent consideration	788	$ 935
Contingent consideration, liability, current	$ 89

Inventories - Narrative (Detail

Inventories - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
LIFO inventory amount	$ 2,500	$ 2,200
Inventories classified in other assets	1,417	1,187
Inventory Not Expected to be Sold Within One Year
Inventory [Line Items]
Inventories classified in other assets	1,400	1,100
Inventories Produced in Preparation for Product Launches
Inventory [Line Items]
Inventories classified in other assets	$ 7	$ 80

Inventories - Inventories (Deta

Inventories - Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Finished goods	$ 1,658	$ 1,334
Raw materials and work in process	5,004	4,703
Supplies	194	201
Total (approximates current cost)	6,856	6,238
Increase to LIFO costs	1	45
Total current and noncurrent inventories	6,857	6,283
Recognized as:
Inventories	5,440	5,096
Other assets	$ 1,417	$ 1,187

Goodwill and Other Intangible_2

Goodwill and Other Intangibles - Goodwill Activity by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 18,284	$ 18,162
Acquisitions	41	177
Impairments	(144)	(38)
Other	72	(17)
Goodwill, Ending Balance	18,253	18,284
Accumulated goodwill impairment losses	369	225
Pharmaceutical
Goodwill [Roll Forward]
Goodwill, Beginning Balance	16,066	16,075
Acquisitions	0	0
Impairments	0	0
Other	96	(9)
Goodwill, Ending Balance	16,162	16,066
Animal Health
Goodwill [Roll Forward]
Goodwill, Beginning Balance	1,877	1,708
Acquisitions	17	177
Impairments	0	0
Other	(24)	(8)
Goodwill, Ending Balance	1,870	1,877
All Other
Goodwill [Roll Forward]
Goodwill, Beginning Balance	341	379
Acquisitions	24	0
Impairments	(144)	(38)
Other	0	0
Goodwill, Ending Balance	$ 221	$ 341

Goodwill and Other Intangible_3

Goodwill and Other Intangibles - Other Intangibles (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Intangible Assets Excluding Goodwill [Line Items]
Gross Carrying Amount	$ 50,291	$ 50,131
Accumulated Amortization	38,860	35,948
Net	11,431	14,183
IPR&D
Intangible Assets Excluding Goodwill [Line Items]
Gross Carrying Amount	1,064	1,194
Net	1,064	1,194
Products and product rights
Intangible Assets Excluding Goodwill [Line Items]
Gross Carrying Amount	46,615	46,693
Accumulated Amortization	37,585	34,950
Net	9,030	11,743
Tradenames
Intangible Assets Excluding Goodwill [Line Items]
Gross Carrying Amount	209	209
Accumulated Amortization	107	97
Net	102	112
Other
Intangible Assets Excluding Goodwill [Line Items]
Gross Carrying Amount	2,403	2,035
Accumulated Amortization	1,168	901
Net	$ 1,235	$ 1,134

Goodwill and Other Intangible_4

Goodwill and Other Intangibles - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net	$ 11,431	$ 14,183
Intangible asset impairment charge related to marketed product		58	$ 347
IPR&D impairment charges	152	483	3,600
Changes in estimated fair value	89	141
Amortization expense for intangible assets	2,900	3,200	3,800
Estimated aggregate amortization expense, 2019	1,500
Estimated aggregate amortization expense, 2020	1,200
Estimated aggregate amortization expense, 2021	1,100
Estimated aggregate amortization expense, 2022	1,100
Estimated aggregate amortization expense, 2023	1,100
Zerbaxa
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net	2,700
Sivextro
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net	833
Implanon/Nexplanon
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net	470
Dificid
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net	395
Gardasil/Gardasil 9
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net	384		468
Bridion
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net	275
Simponi
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net	194
Adempas
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net	1,000
Intron A
Intangible Assets Excluding Goodwill [Line Items]
Intangible asset impairment charge related to marketed product		47
Zontivity
Intangible Assets Excluding Goodwill [Line Items]
Intangible asset impairment charge related to marketed product			252
Grastek/Ragwitek
Intangible Assets Excluding Goodwill [Line Items]
Intangible asset impairment charge related to marketed product			95
SmartCells Program
Intangible Assets Excluding Goodwill [Line Items]
IPR&D impairment charges	139		72
Changes in estimated fair value	$ (60)
uprifosbuvir
Intangible Assets Excluding Goodwill [Line Items]
Other intangibles, net			240
IPR&D impairment charges		240	2,900
verubecestat
Intangible Assets Excluding Goodwill [Line Items]
IPR&D impairment charges		$ 226
monoclonal antibody (cCAM)
Intangible Assets Excluding Goodwill [Line Items]
IPR&D impairment charges			180
BET inhibitor (OncoEthix)
Intangible Assets Excluding Goodwill [Line Items]
IPR&D impairment charges			143
House Dust Mite
Intangible Assets Excluding Goodwill [Line Items]
IPR&D impairment charges			112
Next Generation Ring
Intangible Assets Excluding Goodwill [Line Items]
IPR&D impairment charges			$ 79

Joint Ventures and Other Equi_3

Joint Ventures and Other Equity Method Affiliates - Narrative (Details) $ in Millions	Dec. 31, 2016USD ($)	Jan. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 1998	Dec. 31, 1993
Equity Income from Affiliates [Line Items]
Contingent consideration	$ 891		$ 788	$ 935	$ 891
Proceeds from sale of intangible assets			95	85	170
Other intangibles, net			11,431	14,183
AstraZeneca LP
Equity Income from Affiliates [Line Items]
Ownership percentage (as percent)							50.00%
Limited partner interest in AZLP (as percent)						1.00%
General partner interest in AZLP (as percent)						99.00%
Other income			99	$ 232	98
Recognition of Deferred Revenue					5
AstraZeneca LP | Subsequent Event
Equity Income from Affiliates [Line Items]
Proceeds from sale of interest		$ 424
Gardasil/Gardasil 9
Equity Income from Affiliates [Line Items]
Other intangibles, net	$ 468		$ 384		$ 468
Measurement Input, Discount Rate
Equity Income from Affiliates [Line Items]
Intangible asset, measurement input	0.115				0.115
Step Acquisition and Termination of SPMSD
Equity Income from Affiliates [Line Items]
Equity interest acquired (as percent)	50.00%				50.00%
Consideration transferred in business combination	$ 657
Royalty rate (as percent)	11.50%
Contingent consideration	$ 416				$ 416
Proceeds from sale of intangible assets	596
Fair value of future royalties	$ 302				302
Transaction costs					$ 24
Step Acquisition and Termination of SPMSD | Measurement Input, Discount Rate
Equity Income from Affiliates [Line Items]
Intangible asset, measurement input	0.08				0.08
Sanofi Pasteur MSD
Equity Income from Affiliates [Line Items]
Sales					$ 1,000

Joint Ventures and Other Equi_4

Joint Ventures and Other Equity Method Affiliates - Termination of SPMSD (Details) - Step Acquisition and Termination of SPMSD $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Estimated useful life of intangible assets	8 years
Products and product rights (8-year useful life)	$ 936
Accounts receivable	133
Income taxes payable	(221)
Deferred income tax liabilities	(147)
Other, net	47
Net assets acquired	748
Consideration payable to Sanofi, net	(392)
Derecognition of Merck’s previously held equity investment in SPMSD	(183)
Increase in net assets	173
Merck’s share of restructuring costs related to the termination	(77)
Net gain on termination of SPMSD joint venture	$ 96

Loans Payable, Long-Term Debt_3

Loans Payable, Long-Term Debt and Other Commitments - Narrative (Details) - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Loans payable and current portion of long-term debt		$ 5,308,000,000	$ 3,057,000,000
Long-term debt, current maturities			3,000,000,000
Long-term debt		19,806,000,000	21,353,000,000
Debt extinguishment amount	$ 810,000,000
Repurchased face amount	$ 585,000,000
Loss on extinguishment of debt			191,000,000
Long-term debt, maturities, repayments of principal in 2019		0
Long-term debt, maturities, repayments of principal in 2020		1,900,000,000
Long-term debt, maturities, repayments of principal in 2021		2,300,000,000
Long-term debt, maturities, repayments of principal in 2022		2,200,000,000
Long-term debt, maturities, repayments of principal in 2023		1,700,000,000
Available borrowing capacity under credit facility		6,000,000,000
Rental expense under operating leases net of sublease income		322,000,000	327,000,000	$ 292,000,000
Minimum aggregate rental commitments under noncancellable leases in 2019		188,000,000
Minimum aggregate rental commitments under noncancellable leases in 2020		198,000,000
Minimum aggregate rental commitments under noncancellable leases in 2021		150,000,000
Minimum aggregate rental commitments under noncancellable leases in 2022		134,000,000
Minimum aggregate rental commitments under noncancellable leases in 2023		84,000,000
Minimum aggregate rental commitments under noncancellable leases thereafter		$ 243,000,000
5.00% notes due 2019 | Interest Rate Swap
Debt Instrument [Line Items]
Stated interest rate (as percent)		5.00%
Repurchased face amount		$ 1,250,000,000
Other Variable Rate Debt
Debt Instrument [Line Items]
Long-term debt		$ 223,000,000	$ 300,000,000
Effective interest rate (as percent)		2.27%	1.42%
6.30% debentures due 2026
Debt Instrument [Line Items]
Long-term debt		$ 135,000,000	$ 135,000,000
Stated interest rate (as percent)		6.30%
Notes Subject To Repayment At Option Of Holder
Debt Instrument [Line Items]
Loans payable and current portion of long-term debt		$ 149,000,000	$ 73,000,000
Commercial paper
Debt Instrument [Line Items]
Loans payable and current portion of long-term debt		$ 5,100,000,000
Weighted-average interest rate of commercial paper (as percent)		2.09%	0.85%

Loans Payable, Long-Term Debt_4

Loans Payable, Long-Term Debt and Other Commitments - Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term debt	$ 19,806	$ 21,353
2.75% notes due 2025
Debt Instrument [Line Items]
Long-term debt	$ 2,490	2,488
Stated interest rate (as percent)	2.75%
3.70% notes due 2045
Debt Instrument [Line Items]
Long-term debt	$ 1,974	1,973
Stated interest rate (as percent)	3.70%
2.80% notes due 2023
Debt Instrument [Line Items]
Long-term debt	$ 1,745	1,744
Stated interest rate (as percent)	2.80%
4.15% notes due 2043
Debt Instrument [Line Items]
Long-term debt	$ 1,237	1,237
Stated interest rate (as percent)	4.15%
1.85% notes due 2020
Debt Instrument [Line Items]
Long-term debt	$ 1,231	1,232
Stated interest rate (as percent)	1.85%
2.35% notes due 2022
Debt Instrument [Line Items]
Long-term debt	$ 1,214	1,220
Stated interest rate (as percent)	2.35%
1.125% euro-denominated notes due 2021
Debt Instrument [Line Items]
Long-term debt	$ 1,134	1,185
Stated interest rate (as percent)	1.125%
3.875% notes due 2021
Debt Instrument [Line Items]
Long-term debt	$ 1,132	1,140
Stated interest rate (as percent)	3.875%
1.875% euro-denominated notes due 2026
Debt Instrument [Line Items]
Long-term debt	$ 1,127	1,178
Stated interest rate (as percent)	1.875%
2.40% notes due 2022
Debt Instrument [Line Items]
Long-term debt	$ 983	993
Stated interest rate (as percent)	2.40%
6.50% notes due 2033
Debt Instrument [Line Items]
Long-term debt	$ 726	729
Stated interest rate (as percent)	6.50%
Floating-rate notes due 2020
Debt Instrument [Line Items]
Long-term debt	$ 699	699
0.50% euro-denominated notes due 2024
Debt Instrument [Line Items]
Long-term debt	$ 565	591
Stated interest rate (as percent)	0.50%
1.375% euro-denominated notes due 2036
Debt Instrument [Line Items]
Long-term debt	$ 561	587
Stated interest rate (as percent)	1.375%
2.50% euro-denominated notes due 2034
Debt Instrument [Line Items]
Long-term debt	$ 560	585
Stated interest rate (as percent)	2.50%
3.60% notes due 2042
Debt Instrument [Line Items]
Long-term debt	$ 490	489
Stated interest rate (as percent)	3.60%
6.55% notes due 2037
Debt Instrument [Line Items]
Long-term debt	$ 414	415
Stated interest rate (as percent)	6.55%
5.75% notes due 2036
Debt Instrument [Line Items]
Long-term debt	$ 338	338
Stated interest rate (as percent)	5.75%
5.95% debentures due 2028
Debt Instrument [Line Items]
Long-term debt	$ 306	306
Stated interest rate (as percent)	5.95%
5.85% notes due 2039
Debt Instrument [Line Items]
Long-term debt	$ 270	270
Stated interest rate (as percent)	5.85%
6.40% debentures due 2028
Debt Instrument [Line Items]
Long-term debt	$ 250	250
Stated interest rate (as percent)	6.40%
6.30% debentures due 2026
Debt Instrument [Line Items]
Long-term debt	$ 135	135
Stated interest rate (as percent)	6.30%
5.00% notes due 2019
Debt Instrument [Line Items]
Long-term debt	$ 0	1,260
Stated interest rate (as percent)	5.00%
Other
Debt Instrument [Line Items]
Long-term debt	$ 225	$ 309

Contingencies and Environment_2

Contingencies and Environmental Liabilities - Fosamax Product Liability Litigation - Narrative (Details) - Fosamax - legalmatter	1 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2018	Jul. 31, 2015	Nov. 30, 2013
Loss Contingencies [Line Items]
Loss contingency, pending claims number		3,900
Federal Court
Loss Contingencies [Line Items]
Loss contingency, pending claims number		9
Loss contingency, claims dismissed number	650	1,055
Loss contingency, claims on appeal, number		515
New Jersey State Court
Loss Contingencies [Line Items]
Loss contingency, pending claims number		2,555
Initial number of cases selected for review		30
Subsequent number of cases selected for review	50		25	50
California State Court
Loss Contingencies [Line Items]
Loss contingency, pending claims number		275
Initial number of cases selected for review	10
Other State Court
Loss Contingencies [Line Items]
Loss contingency, pending claims number		4

Contingencies and Environment_3

Contingencies and Environmental Liabilities - Januvia/Janumet Litigation - Narrative (Details) - Januvia	Dec. 31, 2018legalmatter
Loss Contingencies [Line Items]
Loss contingency, pending claims number	1,290
Cases Company Agreed To Toll Statute Of Limitations
Loss Contingencies [Line Items]
Loss contingency, pending claims number	50
Other State Court
Loss Contingencies [Line Items]
Loss contingency, pending claims number	8

Contingencies and Environment_4

Contingencies and Environmental Liabilities - Propecia/Proscar Litigation - Narrative (Details) - Propecia/Proscar $ in Millions	Apr. 09, 2018USD ($)	Dec. 31, 2018legalmatter
Loss Contingencies [Line Items]
Settlement awarded to other party | $	$ 4.3
Plaintiff participation in litigation settlement (as percent)	95.00%
Loss contingency, pending claims number | legalmatter		25

Contingencies and Environment_5

Contingencies and Environmental Liabilities - Commercial and Other Litigation- Narrative (Details) - Commercial Litigation $ in Millions	Oct. 01, 2018USD ($)legalmatter	Apr. 29, 2016legalmatter	Jan. 31, 2014legalmatter	Dec. 31, 2018legalmatter
Loss Contingencies [Line Items]
Additional claims filed		1	4
Loss contingency, pending claims number				700
Settlement awarded to other party | $	$ 8.5
Minimum plaintiffs opting out for opt-out clause in settlement award	30
Number of plaintiffs				2
Loss contingency, claims on appeal, number				2

Contingencies and Environment_6

Contingencies and Environmental Liabilities - Patent Litigation - Narrative (Details) $ in Millions	1 Months Ended		12 Months Ended
	Jan. 31, 2018USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)legalmatter	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Gain Contingencies [Line Items]
Litigation settlement, gain (loss)			$ 0	$ 0	$ (625)
Number of patents allegedly infringed upon | legalmatter			2
Patent litigation
Gain Contingencies [Line Items]
Litigation settlement, gain (loss)	$ 115
Settlement awarded to company		$ 2,540

Contingencies and Environment_7

Contingencies and Environmental Liabilities - Legal Defense Reserves - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Legal Defense Costs
Loss Contingencies [Line Items]
Legal defense costs reserve	$ 245	$ 160

Contingencies and Environment_8

Contingencies and Environmental Liabilities - Environmental Litigation and Matters - Narrative (Details) € in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2012USD ($)	Dec. 31, 2017USD ($)
Site Contingency [Line Items]
Accrued liabilities for environmental matters	$ 71,000			$ 82,000
Term for paying off environmental liabilities	15 years	15 years
Aggregate possible expenditure on environmental matters in excess of amounts accrued	$ 60,000
Oss Netherlands
Site Contingency [Line Items]
Environmental remediation expense		€ 400	$ 235

Equity - Narrative (Details)

Equity - Narrative (Details) - USD ($) $ in Millions	Oct. 29, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 25, 2018
Equity [Abstract]
Common stock, shares authorized		6,500,000,000	6,500,000,000
Preferred stock, shares authorized		20,000,000
Accelerated Share Repurchases [Line Items]
Treasury stock acquired		$ 9,091	$ 4,014	$ 3,434
Accelerated Share Repurchase Agreement, October 29, 2018
Accelerated Share Repurchases [Line Items]
Purchases of treasury stock (in shares)	56,700,000
Accelerated Share Repurchase Agreement
Accelerated Share Repurchases [Line Items]
Shares authorized to be repurchased (in shares)					$ 5,000
Payment under ASR agreement	$ 5,000
Treasury stock acquired	4,000
Decrease in other-paid-in capital	$ 1,000

Equity - Shareholders' Equity (

Equity - Shareholders' Equity (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement in Common Stock and Treasury Stock [Roll Forward]
Balance January 1 (in shares)	3,577,103,522
Balance December 31 (in shares)	3,577,103,522	3,577,103,522
Common Stock
Movement in Common Stock and Treasury Stock [Roll Forward]
Balance January 1 (in shares)	3,577,000,000	3,577,000,000	3,577,000,000
Purchases of treasury stock (in shares)	0	0	0
Issuances (in shares)	0	0	0
Balance December 31 (in shares)	3,577,000,000	3,577,000,000	3,577,000,000
Treasury Stock
Movement in Common Stock and Treasury Stock [Roll Forward]
Balance January 1 (in shares)	880,000,000	828,000,000	796,000,000
Purchases of treasury stock (in shares)	122,000,000	67,000,000	60,000,000
Issuances (in shares)	(17,000,000)	(15,000,000)	(28,000,000)
Balance December 31 (in shares)	985,000,000	880,000,000	828,000,000

Share-Based Compensation Plan_2

Share-Based Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares collectively authorized for future grants under share-based compensation plans (in shares)	111,000,000
Quantity of stock options that vest per year (as percent)	33.33%
Period over which share-based payment awards vest	3 years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax share-based compensation cost	$ 348	$ 312	$ 300
Income tax benefits related to share-based compensation	$ 55	$ 57	$ 92
Weighted average exercise price of options granted (in dollars per share)	$ 58.15	$ 63.88	$ 54.63
Weighted average fair value of options granted (in dollars per share)	$ 8.26	$ 7.04	$ 5.89
Total pre tax unrecognized compensation expense related to nonvested stock options, RSU and PSU awards	$ 560
Weighted average period in years of recognition for nonvested stock options, RSU and PSU awards	1 year 10 months 25 days
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term of options	7 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term of options	10 years

Share-Based Compensation Plan_3

Share-Based Compensation Plans - Assumptions Used to Determine Weighted-Average Fair Value of Options Granted (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected dividend yield	3.40%	3.60%	3.80%
Risk-free interest rate	2.90%	2.00%	1.40%
Expected volatility	19.10%	17.80%	19.60%
Expected life (years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 2 months 12 days

Share-Based Compensation Plan_4

Share-Based Compensation Plans - Summary of Information Relative to Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding, January 1 (in shares)	36,274
Number of Options, Granted (in shares)	3,520
Number of Options, Exercised (in shares)	(14,598)
Number of Options, Forfeited (in shares)	(1,389)
Number of Options, Outstanding, December 31 (in shares)	23,807	36,274
Number of Options, Exercisable (in shares)	16,184
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Options Outstanding, January 1 (in dollars per share)	$ 46.77
Weighted Average Exercise Price, Granted (in dollars per share)	58.15	$ 63.88	$ 54.63
Weighted Average Exercise Price, Exercised (in dollars per share)	40.51
Weighted Average Exercise Price, Forfeited (in dollars per share)	53.80
Weighted Average Exercise Price, Options Outstanding, December 31 (in dollars per share)	51.89	$ 46.77
Weighted Average Exercise Price, Exercisable (in dollars per share)	$ 48.85
Weighted Average Remaining Contractual Term, Outstanding	5 years 11 months 12 days
Weighted Average Remaining Contractual Term, Exercisable	4 years 9 months 25 days
Aggregate Intrinsic Value, Outstanding	$ 584
Aggregate Intrinsic Value, Exercisable	$ 446

Share-Based Compensation Plan_5

Share-Based Compensation Plans - Additional Information Pertaining to Stock Option Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total intrinsic value of stock options exercised	$ 348	$ 236	$ 444
Fair value of stock options vested	29	30	28
Cash received from the exercise of stock options	$ 591	$ 499	$ 939

Share-Based Compensation Plan_6

Share-Based Compensation Plans - Summary of Nonvested RSU and PSU Activity (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2018$ / sharesshares
RSUs
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of Shares, Nonvested January 1 | shares	13,609
Number of Shares, Granted | shares	7,270
Number of Shares, Vested | shares	(3,766)
Number of Shares, Forfeited | shares	(985)
Number of Shares, Nonvested December 31 | shares	16,128
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value, Nonvested January 1 (in dollars per share) | $ / shares	$ 59.32
Weighted Average Grant Date Fair Value, Granted (in dollars per share) | $ / shares	58.46
Weighted Average Grant Date Fair Value, Vested (in dollars per share) | $ / shares	59.66
Weighted Average Grant Date Fair Value, Forfeited (in dollars per share) | $ / shares	59.30
Weighted Average Grant Date Fair Value, Nonvested December 31 (in dollars per share) | $ / shares	$ 58.85
PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of Shares, Nonvested January 1 | shares	1,868
Number of Shares, Granted | shares	1,081
Number of Shares, Vested | shares	(758)
Number of Shares, Forfeited | shares	(152)
Number of Shares, Nonvested December 31 | shares	2,039
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value, Nonvested January 1 (in dollars per share) | $ / shares	$ 60.03
Weighted Average Grant Date Fair Value, Granted (in dollars per share) | $ / shares	57.17
Weighted Average Grant Date Fair Value, Vested (in dollars per share) | $ / shares	57.59
Weighted Average Grant Date Fair Value, Forfeited (in dollars per share) | $ / shares	60.06
Weighted Average Grant Date Fair Value, Nonvested December 31 (in dollars per share) | $ / shares	$ 59.42

Pension and Other Postretirem_3

Pension and Other Postretirement Benefit Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 19,000	$ 20,500
Employer contributions to defined contribution savings plans		$ 136	$ 131	$ 126
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Percentage of Company's pension investments categorized as Level 3 assets (as percent)		5.00%	2.00%
Estimated net loss (gain) amounts that will be amortized from AOCI into net pension and postretirement benefit cost during next fiscal year		$ 204
Estimated prior service cost (credit) amounts that will be amortized from AOCI into net pension and postretirement benefit cost during next fiscal year		(62)
Pension Benefits | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		826	$ 488
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		968	1,114	$ 1,019
Expected contributions to the pension plans and other postretirement benefit plans during next fiscal year		15
Estimated net loss (gain) amounts that will be amortized from AOCI into net pension and postretirement benefit cost during next fiscal year		(7)
Estimated prior service cost (credit) amounts that will be amortized from AOCI into net pension and postretirement benefit cost during next fiscal year		(78)
Other Postretirement Benefits | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 0	$ 0
United States
Defined Benefit Plan Disclosure [Line Items]
Expected annual standard deviation in returns of the target portfolio which reflects both the equity allocation and the diversification benefits among the asset classes in which the portfolio invests (as percent)		11.00%
Expected rate of return on plan assets (as percent)		8.20%	8.70%	8.60%
United States | Minimum
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets (as percent)		7.70%
United States | Minimum | Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets (as percent)	7.70%
United States | Maximum
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets (as percent)		8.30%
United States | Maximum | Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets (as percent)	8.10%
United States | U.S. equities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		30.00%
United States | U.S. equities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		50.00%
United States | International equities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		15.00%
United States | International equities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		30.00%
United States | Fixed Income Investments | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		30.00%
United States | Fixed Income Investments | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		45.00%
United States | Cash And Other Investments | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		5.00%
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 10,400	$ 11,500
Fair value of plan assets		9,648	10,896	$ 9,766
Expected contributions to the pension plans and other postretirement benefit plans during next fiscal year		50
Estimated net loss (gain) amounts that will be amortized from AOCI into net pension and postretirement benefit cost during next fiscal year		141
Estimated prior service cost (credit) amounts that will be amortized from AOCI into net pension and postretirement benefit cost during next fiscal year		(50)
United States | Pension Benefits | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		13	15	18
International | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		8,580	$ 9,339	$ 7,794
Expected contributions to the pension plans and other postretirement benefit plans during next fiscal year		$ 150
Expected rate of return on plan assets (as percent)		5.10%	5.10%	5.60%
International | Pension Benefits | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 813	$ 473	$ 417

Pension and Other Postretirem_4

Pension and Other Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 57	$ 57	$ 54
Interest cost	69	81	82
Expected return on plan assets	(83)	(78)	(107)
Amortization of unrecognized prior service cost	(84)	(98)	(106)
Net loss amortization	1	1	3
Termination benefits	3	8	4
Curtailments	(8)	(31)	(18)
Settlements	0	0	0
Net periodic benefit cost (credit)	(45)	(60)	(88)
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	326	312	282
Interest cost	432	454	456
Expected return on plan assets	(851)	(862)	(831)
Amortization of unrecognized prior service cost	(50)	(53)	(55)
Net loss amortization	232	180	119
Termination benefits	19	44	23
Curtailments	10	3	5
Settlements	5	0	0
Net periodic benefit cost (credit)	123	78	(1)
International | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	238	252	238
Interest cost	178	172	204
Expected return on plan assets	(431)	(393)	(382)
Amortization of unrecognized prior service cost	(13)	(11)	(11)
Net loss amortization	84	98	87
Termination benefits	2	4	4
Curtailments	1	(4)	(1)
Settlements	13	5	6
Net periodic benefit cost (credit)	$ 72	$ 123	$ 145

Pension and Other Postretirem_5

Pension and Other Postretirement Benefit Plans - Obligation and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Postretirement Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	$ 1,114	$ 1,019
Actual return on plan assets	(72)	161
Company contributions, net	6	(4)
Effects of exchange rate changes	0	0
Benefits paid	(80)	(62)
Settlements	0	0
Other	0	0
Fair value of plan assets December 31	968	1,114	$ 1,019
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	1,922	1,922
Service cost	57	57	54
Interest cost	69	81	82
Actuarial (gains) losses	(341)	(87)
Benefits paid	(80)	(62)
Effects of exchange rate changes	(6)	3
Plan amendments	(9)	0
Curtailments	0	0
Termination benefits	3	8	4
Settlements	0	0
Other	0	0
Benefit obligation December 31	1,615	1,922	1,922
Funded status December 31	(647)	(808)
Recognized as:
Other assets	0	0
Accrued and other current liabilities	(10)	(11)
Other noncurrent liabilities	(637)	(797)
United States | Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	10,896	9,766
Actual return on plan assets	(810)	1,723
Company contributions, net	378	58
Effects of exchange rate changes	0	0
Benefits paid	(772)	(651)
Settlements	(44)	0
Other	0	0
Fair value of plan assets December 31	9,648	10,896	9,766
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	11,904	10,849
Service cost	326	312	282
Interest cost	432	454	456
Actuarial (gains) losses	(1,258)	881
Benefits paid	(772)	(651)
Effects of exchange rate changes	0	0
Plan amendments	0	0
Curtailments	13	15
Termination benefits	19	44	23
Settlements	(44)	0
Other	0	0
Benefit obligation December 31	10,620	11,904	10,849
Funded status December 31	(972)	(1,008)
Recognized as:
Other assets	0	0
Accrued and other current liabilities	(47)	(59)
Other noncurrent liabilities	(925)	(949)
International | Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	9,339	7,794
Actual return on plan assets	(289)	677
Company contributions, net	167	226
Effects of exchange rate changes	(352)	843
Benefits paid	(202)	(198)
Settlements	(106)	(17)
Other	23	14
Fair value of plan assets December 31	8,580	9,339	7,794
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	9,483	8,372
Service cost	238	252	238
Interest cost	178	172	204
Actuarial (gains) losses	(154)	(7)
Benefits paid	(202)	(198)
Effects of exchange rate changes	(387)	916
Plan amendments	10	(22)
Curtailments	(2)	(3)
Termination benefits	2	4	4
Settlements	(106)	(17)
Other	23	14
Benefit obligation December 31	9,083	9,483	$ 8,372
Funded status December 31	(503)	(144)
Recognized as:
Other assets	659	828
Accrued and other current liabilities	(14)	(17)
Other noncurrent liabilities	$ (1,148)	$ (955)

Pension and Other Postretirem_6

Pension and Other Postretirement Benefit Plans - Accumulated and Projected Benefit Obligation in Excess of Plan Assets (Details) - Pension Benefits - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plans with a projected benefit obligation in excess of plan assets, projected benefit obligation	$ 10,620	$ 11,904
Pension plans with a projected benefit obligation in excess of plan assets, fair value of plan assets	9,648	10,896
Pension plans with an accumulated benefit obligation in excess of plan assets, accumulated benefit obligation	9,702	676
Pension plans with an accumulated benefit obligation in excess of plan assets, fair value of plan assets	8,966	0
International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plans with a projected benefit obligation in excess of plan assets, projected benefit obligation	6,251	3,323
Pension plans with a projected benefit obligation in excess of plan assets, fair value of plan assets	5,089	2,352
Pension plans with an accumulated benefit obligation in excess of plan assets, accumulated benefit obligation	5,936	2,120
Pension plans with an accumulated benefit obligation in excess of plan assets, fair value of plan assets	$ 5,071	$ 1,346

Pension and Other Postretirem_7

Pension and Other Postretirement Benefit Plans - Fair Values of Pension Plan Assets (Details) - Pension Benefits - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 826	$ 488
United States
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9,648	10,896	$ 9,766
United States | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,532	5,189
United States | Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40	6
United States | Fair Value, Inputs, Level 1, 2 and 3 | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	169	390
United States | Fair Value, Inputs, Level 1, 2 and 3 | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	121	138
United States | Fair Value, Inputs, Level 1, 2 and 3 | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,172	2,743
United States | Fair Value, Inputs, Level 1, 2 and 3 | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,509	757
United States | Fair Value, Inputs, Level 1, 2 and 3 | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,246	900
United States | Fair Value, Inputs, Level 1, 2 and 3 | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	262	240
United States | Fair Value, Inputs, Level 1, 2 and 3 | Other, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13	15
United States | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,502	3,277
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40	6
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	169	390
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	121	138
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,172	2,743
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Other, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,017	1,897
United States | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Other Observable Inputs (Level 2) | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Other Observable Inputs (Level 2) | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Other Observable Inputs (Level 2) | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Other Observable Inputs (Level 2) | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,509	757
United States | Significant Other Observable Inputs (Level 2) | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,246	900
United States | Significant Other Observable Inputs (Level 2) | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	262	240
United States | Significant Other Observable Inputs (Level 2) | Other, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13	15	18
United States | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Unobservable Inputs (Level 3) | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Unobservable Inputs (Level 3) | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Unobservable Inputs (Level 3) | Real estate, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	0
United States | Significant Unobservable Inputs (Level 3) | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Unobservable Inputs (Level 3) | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Unobservable Inputs (Level 3) | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Unobservable Inputs (Level 3) | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
United States | Significant Unobservable Inputs (Level 3) | Insurance contracts, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	0
United States | Significant Unobservable Inputs (Level 3) | Other, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13	15	18
United States | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,116	5,707
International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,580	9,339	7,794
International | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,119	8,537
International | Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	53	73
International | Fair Value, Inputs, Level 1, 2 and 3 | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,532	3,888
International | Fair Value, Inputs, Level 1, 2 and 3 | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	168	238
International | Fair Value, Inputs, Level 1, 2 and 3 | Government and agency obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,454	2,344
International | Fair Value, Inputs, Level 1, 2 and 3 | Corporate obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	334
International | Fair Value, Inputs, Level 1, 2 and 3 | Fixed income obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	11
International | Fair Value, Inputs, Level 1, 2 and 3 | Real estate, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	3
International | Fair Value, Inputs, Level 1, 2 and 3 | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	544	660
International | Fair Value, Inputs, Level 1, 2 and 3 | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	293	268
International | Fair Value, Inputs, Level 1, 2 and 3 | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	114	119
International | Fair Value, Inputs, Level 1, 2 and 3 | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55	55
International | Fair Value, Inputs, Level 1, 2 and 3 | Insurance contracts, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	877	537
International | Fair Value, Inputs, Level 1, 2 and 3 | Other, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	7
International | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,497	1,602
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	50	54
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	461	562
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	56	62
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Government and agency obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	372	249
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4	5
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Fixed income obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7	7
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Real estate, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	544	660
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	2
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Insurance contracts, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Other, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,809	6,462
International | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	19
International | Significant Other Observable Inputs (Level 2) | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,071	3,326
International | Significant Other Observable Inputs (Level 2) | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	112	176
International | Significant Other Observable Inputs (Level 2) | Government and agency obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,082	2,095
International | Significant Other Observable Inputs (Level 2) | Corporate obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7	329
International | Significant Other Observable Inputs (Level 2) | Fixed income obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4	4
International | Significant Other Observable Inputs (Level 2) | Real estate, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
International | Significant Other Observable Inputs (Level 2) | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Other Observable Inputs (Level 2) | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	291	266
International | Significant Other Observable Inputs (Level 2) | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	113	118
International | Significant Other Observable Inputs (Level 2) | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55	55
International | Significant Other Observable Inputs (Level 2) | Insurance contracts, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	66	67
International | Significant Other Observable Inputs (Level 2) | Other, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4	6
International | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	813	473	417
International | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Government and agency obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Corporate obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Fixed income obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Real estate, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	2	4
International | Significant Unobservable Inputs (Level 3) | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Insurance contracts, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	811	470	412
International | Significant Unobservable Inputs (Level 3) | Other, Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1	$ 1
International | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 461	$ 802

Pension and Other Postretirem_8

Pension and Other Postretirement Benefit Plans - Summary of Changes in Fair Value of Company's Level 3 Pension Plan Assets (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	$ 488
Actual return on plan assets:
Fair value of plan assets December 31	826	$ 488
United States
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	10,896	9,766
Actual return on plan assets:
Fair value of plan assets December 31	9,648	10,896
United States | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	15	18
Actual return on plan assets:
Relating to assets still held at December 31	(3)	(2)
Relating to assets sold during the year	4	4
Purchases and sales, net	(3)	(5)
Fair value of plan assets December 31	13	15
United States | Significant Unobservable Inputs (Level 3) | Insurance Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	0	0
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Relating to assets sold during the year	0	0
Purchases and sales, net	0	0
Fair value of plan assets December 31	0	0
United States | Significant Unobservable Inputs (Level 3) | Real Estate
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	0	0
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Relating to assets sold during the year	0	0
Purchases and sales, net	0	0
Fair value of plan assets December 31	0	0
United States | Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	15	18
Actual return on plan assets:
Relating to assets still held at December 31	(3)	(2)
Relating to assets sold during the year	4	4
Purchases and sales, net	(3)	(5)
Fair value of plan assets December 31	13	15
International
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	9,339	7,794
Actual return on plan assets:
Fair value of plan assets December 31	8,580	9,339
International | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	473	417
Actual return on plan assets:
Relating to assets still held at December 31	(32)	52
Purchases and sales, net	379	3
Transfers into Level 3	(7)	1
Fair value of plan assets December 31	813	473
International | Significant Unobservable Inputs (Level 3) | Insurance Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	470	412
Actual return on plan assets:
Relating to assets still held at December 31	(32)	52
Purchases and sales, net	380	5
Transfers into Level 3	(7)	1
Fair value of plan assets December 31	811	470
International | Significant Unobservable Inputs (Level 3) | Real Estate
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	2	4
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Purchases and sales, net	(1)	(2)
Transfers into Level 3	0	0
Fair value of plan assets December 31	1	2
International | Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	1	1
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Purchases and sales, net	0	0
Transfers into Level 3	0	0
Fair value of plan assets December 31	$ 1	$ 1

Pension and Other Postretirem_9

Pension and Other Postretirement Benefit Plans - Fair Values of Other Postretirement Benefit Plan Assets (Details) - Other Postretirement Benefits - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 968	$ 1,114	$ 1,019
Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	588	582
Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	78	97
Fair Value, Inputs, Level 1, 2 and 3 | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	16	37
Fair Value, Inputs, Level 1, 2 and 3 | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	12	13
Fair Value, Inputs, Level 1, 2 and 3 | Government and agency obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1	1
Fair Value, Inputs, Level 1, 2 and 3 | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	200	256
Fair Value, Inputs, Level 1, 2 and 3 | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	141	71
Fair Value, Inputs, Level 1, 2 and 3 | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	116	84
Fair Value, Inputs, Level 1, 2 and 3 | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	24	23
Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	307	404
Quoted Prices In Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	78	97
Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	16	37
Quoted Prices In Active Markets for Identical Assets (Level 1) | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	12	13
Quoted Prices In Active Markets for Identical Assets (Level 1) | Government and agency obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1	1
Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	200	256
Quoted Prices In Active Markets for Identical Assets (Level 1) | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Quoted Prices In Active Markets for Identical Assets (Level 1) | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	281	178
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Other Observable Inputs (Level 2) | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Other Observable Inputs (Level 2) | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Other Observable Inputs (Level 2) | Government and agency obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Other Observable Inputs (Level 2) | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Other Observable Inputs (Level 2) | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	141	71
Significant Other Observable Inputs (Level 2) | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	116	84
Significant Other Observable Inputs (Level 2) | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	24	23
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Developed markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Emerging markets equities, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Government and agency obligations, Investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Developed markets, Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Government and agency obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Corporate obligations, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Mortgage and asset backed-securities, Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 380	$ 532

Pension and Other Postretire_10

Pension and Other Postretirement Benefit Plans - Summary of Expected Benefit Payments (Details) $ in Millions	Dec. 31, 2018USD ($)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
2,019	$ 91
2,020	95
2,021	98
2,022	102
2,023	105
2024 — 2028	577
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
2,019	638
2,020	661
2,021	680
2,022	685
2,023	709
2024 — 2028	3,805
International | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
2,019	225
2,020	213
2,021	221
2,022	239
2,023	249
2024 — 2028	$ 1,349

Pension and Other Postretire_11

Pension and Other Postretirement Benefit Plans - Components of Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net loss amortization included in benefit cost	$ 186	$ 170	$ (45)
Prior service (cost) credit arising during the period	2	(31)	(19)
Total	188	139	(64)
Net loss amortization included in benefit cost	1	1	3
Prior service (credit) cost amortization included in benefit cost	(84)	(98)	(106)
Total	(83)	(97)	(103)
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net loss amortization included in benefit cost	(397)	(19)	(743)
Prior service (cost) credit arising during the period	(4)	(13)	(10)
Total	(401)	(32)	(753)
Net loss amortization included in benefit cost	232	180	119
Prior service (credit) cost amortization included in benefit cost	(50)	(53)	(55)
Total	182	127	64
International | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net loss amortization included in benefit cost	(505)	309	(380)
Prior service (cost) credit arising during the period	(10)	22	(2)
Total	(515)	331	(382)
Net loss amortization included in benefit cost	84	98	87
Prior service (credit) cost amortization included in benefit cost	(13)	(11)	(11)
Total	$ 71	$ 87	$ 76

Pension and Other Postretire_12

Pension and Other Postretirement Benefit Plans - Summary of Weighted Average Assumptions Used in Determining Pension Plan and U.S. Pension and Other Postretirement Benefit Plan Information (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
United States
Net periodic benefit cost
Discount rate	3.70%	4.30%	4.70%
Expected rate of return on plan assets	8.20%	8.70%	8.60%
Salary growth rate	4.30%	4.30%	4.30%
Benefit obligation
Discount rate	4.40%	3.70%	4.30%
Salary growth rate	4.30%	4.30%	4.30%
International | Pension Benefits
Net periodic benefit cost
Discount rate	2.10%	2.20%	2.80%
Expected rate of return on plan assets	5.10%	5.10%	5.60%
Salary growth rate	2.90%	2.90%	2.90%
Benefit obligation
Discount rate	2.20%	2.10%	2.20%
Salary growth rate	2.80%	2.90%	2.90%

Pension and Other Postretire_13

Pension and Other Postretirement Benefit Plans - Summary of Health Care Cost Trend Rate Assumptions for Other Postretirement Benefit Plans (Details) - Other Postretirement Benefits	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate assumed for next year	7.00%	7.20%
Rate to which the cost trend rate is assumed to decline	4.50%	4.50%

Pension and Other Postretire_14

Pension and Other Postretirement Benefit Plans - One Percentage Point Change in Health Care Cost Trend Rate (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Retirement Benefits [Abstract]
Effect on total service and interest cost components, Increase	$ 11
Effect on benefit obligation, Increase	88
Effect on total service and interest cost components, Decrease	(9)
Effect on benefit obligation, Decrease	$ (74)

Other (Income) Expense, Net (De

Other (Income) Expense, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Income and Expenses [Abstract]
Interest income	$ (343)	$ (385)	$ (328)
Interest expense	772	754	693
Exchange losses (gains)	145	(11)	174
Income on investments in equity securities, net	(324)	(352)	(43)
Net periodic defined benefit plan (credit) cost other than service cost	(512)	(512)	(531)
Other, net	(140)	6	224
Other (income) expense, net	$ (402)	$ (500)	$ 189

Other (Income) Expense, Net - N

Other (Income) Expense, Net - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Component of Other Income / Expense of Nonoperating [Line Items]
Litigation settlement, gain (loss)	$ 0	$ 0	$ (625)
Goodwill impairment charges	144	38
Write-down of assets held for sale	41
Loss on extinguishment of debt		191
Interest paid	777	723	686
Healthcare Services
Component of Other Income / Expense of Nonoperating [Line Items]
Goodwill impairment charges	144
CGRP receptor antagonists
Component of Other Income / Expense of Nonoperating [Line Items]
Gain (loss) on sale of clinical development programs	85		100
AstraZeneca LP
Component of Other Income / Expense of Nonoperating [Line Items]
Other income	99	$ 232	98
Patent litigation
Component of Other Income / Expense of Nonoperating [Line Items]
Litigation settlement, gain (loss)	$ 115		$ 117

Taxes on Income - Narrative (De

Taxes on Income - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
U.S. statutory rate applied to income before taxes (as percent)	21.00%	35.00%	35.00%
Impact of the TCJA (as percent)	3.30%	40.30%	0.00%
Charge for one-time transition tax related to Tax Cuts and Jobs Act of 2017	$ 0	$ 5,347,000,000	$ 0
Reversal of deferred tax previously recorded		2,000,000,000
Measurement-period adjustment	124,000,000
Transition tax liability	4,900,000,000	5,500,000,000
Remeasurement of deferred taxes related to Tax Cuts and Jobs Act of 2017 provisional benefit		779,000,000
Measurement period adjustments related to deferred income taxes	32,000,000
Deferred tax assets on NOL carryforwards relating to foreign jurisdictions	715,000,000
NOL carryforwards relating to U.S. jurisdictions	0
Income taxes paid	1,500,000,000	4,900,000,000	1,800,000,000
Tax benefits relating to stock option exercises	77,000,000	73,000,000	147,000,000
Unrecognized tax benefits	1,893,000,000	1,723,000,000	3,494,000,000	$ 3,448,000,000
Favorable net impact to income tax provision if unrecognized tax benefits were recognized	1,800,000,000
Reasonably possible amount that liability for unrecognized tax benefits could decline up to in next 12 months (up to)	750,000,000
Interest and penalties associated with uncertain tax positions, expense (benefit)	51,000,000	183,000,000	134,000,000
Liabilities for accrued interest and penalties	372,000,000	341,000,000
Unrecognized tax benefits from adjustments related to examination	91,000,000	1,388,000,000	$ 92,000,000
Foreign Jurisdiction
Income Tax [Line Items]
Valuation allowance on foreign NOL carryforwards	1,300,000,000
Federal | Internal Revenue Service (IRS)
Income Tax [Line Items]
Income taxes paid		2,800,000,000
Unrecognized tax benefits from adjustments related to examination		$ 234,000,000
Income Taxes Payable
Income Tax [Line Items]
Transition tax liability, current	275,000,000
Other Noncurrent Liabilities
Income Tax [Line Items]
Transition tax liability, noncurrent	$ 4,600,000,000

Taxes on Income - Reconciliatio

Taxes on Income - Reconciliation Between Effective Tax Rate and US Statutory Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amount
U.S. statutory rate applied to income before taxes	$ 1,827	$ 2,282	$ 1,631
Differential arising from:
Impact of the TCJA	289	2,625	0
Valuation allowances	269	632	(5)
Impact of purchase accounting adjustments, including amortization	267	713	623
State taxes	201	77	173
Restructuring	56	142	145
Foreign earnings	(245)	(1,654)	(1,546)
R&D tax credit	(96)	(71)	(58)
Tax settlements	(22)	(356)	0
Other	(38)	(287)	(245)
Taxes on income	$ 2,508	$ 4,103	$ 718
Tax Rate
U.S. statutory rate applied to income before taxes	21.00%	35.00%	35.00%
Differential arising from:
Impact of the TCJA	3.30%	40.30%	0.00%
Valuation allowances	3.10%	9.70%	(0.10%)
Impact of purchase accounting adjustments, including amortization	3.10%	10.90%	13.40%
State taxes	2.30%	1.20%	3.70%
Restructuring	0.60%	2.20%	3.10%
Foreign earnings	(2.80%)	(25.40%)	(33.20%)
R&D tax credit	(1.10%)	(1.10%)	(1.30%)
Tax settlements	(0.30%)	(5.50%)	0.00%
Other	(0.40%)	(4.40%)	(5.20%)
Total, Tax Rate	28.80%	62.90%	15.40%

Taxes on Income - Income Before

Taxes on Income - Income Before Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Domestic	$ 3,717	$ 3,483	$ 518
Foreign	4,984	3,038	4,141
Income Before Taxes	$ 8,701	$ 6,521	$ 4,659

Taxes on Income - Taxes on Inco

Taxes on Income - Taxes on Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current provision
Federal	$ 536	$ 5,585	$ 1,166
Foreign	2,281	1,229	916
State	200	(90)	157
Total current provision	3,017	6,724	2,239
Deferred provision
Federal	(402)	(2,958)	(1,255)
Foreign	(64)	75	(225)
State	(43)	262	(41)
Total deferred provision	(509)	(2,621)	(1,521)
Taxes on income	$ 2,508	$ 4,103	$ 718

Taxes on Income - Deferred Inco

Taxes on Income - Deferred Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Tax [Line Items]
Product intangibles and licenses, Assets	$ 720	$ 307
Inventory related, Assets	32	29
Accelerated depreciation, Assets	0	28
Pensions and other postretirement benefits, Assets	565	498
Compensation related, Assets	291	314
Unrecognized tax benefits, Assets	174	156
Net operating losses and other tax credit carryforwards, Assets	715	654
Other, Assets	621	909
Subtotal, Assets	3,118	2,895
Valuation allowance, Assets	(1,348)	(900)
Deferred Tax Assets	1,770	1,995
Intangibles, Liabilities	1,640	2,256
Inventory related, Liabilities	377	499
Accelerated depreciation, Liabilities	582	642
Pensions and other postretirement benefits, Liabilities	151	192
Other, Liabilities	66	52
Subtotal, Liabilities	2,816	3,641
Deferred income taxes, Liabilities	1,046	1,646
Deferred income taxes	1,702	2,219
Other assets
Income Tax [Line Items]
Deferred Tax Assets	$ 656	$ 573

Taxes on Income - Unrecognized

Taxes on Income - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Balance January 1	$ 1,723	$ 3,494	$ 3,448
Additions related to current year positions	221	146	196
Additions related to prior year positions	142	520	75
Reductions for tax positions of prior years	(73)	(1,038)	(90)
Settlements	(91)	(1,388)	(92)
Lapse of statute of limitations	(29)	(11)	(43)
Balance December 31	$ 1,893	$ 1,723	$ 3,494

Earnings Per Share - Narrative

Earnings Per Share - Narrative (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Common shares issuable under share-based compensation plans excluded from diluted earnings per common share because the effect would have been antidilutive	6	5	13

Earnings Per Share - Calculatio

Earnings Per Share - Calculations of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income attributable to Merck & Co., Inc.	$ 6,220	$ 2,394	$ 3,920
Average common shares outstanding (in shares)	2,664	2,730	2,766
Common shares issuable (in shares)	15	18	21
Average common shares outstanding assuming dilution (in shares)	2,679	2,748	2,787
Basic earnings per common share attributable to Merck & Co., Inc. common shareholders (in dollars per share)	$ 2.34	$ 0.88	$ 1.42
Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders (in dollars per share)	$ 2.32	$ 0.87	$ 1.41

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) - Changes in AOCI by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 34,569	$ 40,308	$ 44,767
Other comprehensive income (loss), net of taxes	(361)	316	(1,078)
Adoption of ASU 2018-02 (see Note 2)	(266)
Adoption of new accounting standards (see Note 2)	48
Ending Balance	26,882	34,569	40,308
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(108)	338	404
Other comprehensive income (loss) before reclassification adjustments, pretax	228	(561)	210
Tax	(55)	207	(72)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	173	(354)	138
Reclassification adjustments, pretax	157	(141)	(314)
Tax	(33)	49	110
Reclassification adjustments, net of taxes	124	(92)	(204)
Other comprehensive income (loss), net of taxes	297	(446)	(66)
Adoption of ASU 2018-02 (see Note 2)	(23)
Adoption of new accounting standards (see Note 2)				$ 0
Ending Balance	166	(108)	338
Investments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(61)	(3)	41
Other comprehensive income (loss) before reclassification adjustments, pretax	(108)	212	(38)
Tax	1	(35)	16
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(107)	177	(22)
Reclassification adjustments, pretax	97	(291)	(31)
Tax	0	56	9
Reclassification adjustments, net of taxes	97	(235)	(22)
Other comprehensive income (loss), net of taxes	(10)	(58)	(44)
Adoption of ASU 2018-02 (see Note 2)	1
Adoption of new accounting standards (see Note 2)				(8)
Ending Balance	(78)	(61)	(3)
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(2,787)	(3,206)	(2,407)
Other comprehensive income (loss) before reclassification adjustments, pretax	(728)	438	(1,199)
Tax	169	(106)	363
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(559)	332	(836)
Reclassification adjustments, pretax	170	117	37
Tax	(36)	(30)	0
Reclassification adjustments, net of taxes	134	87	37
Other comprehensive income (loss), net of taxes	(425)	419	(799)
Adoption of ASU 2018-02 (see Note 2)	(344)
Adoption of new accounting standards (see Note 2)				0
Ending Balance	(3,556)	(2,787)	(3,206)
Pension Plan Net Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Pension and other postretirement benefit plans, net loss and prior service credit included in AOCI	4,400	3,500
Other Postretirement Benefit Plan Net Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Pension and other postretirement benefit plans, net loss and prior service credit included in AOCI	(170)	(16)
Pension Plan Prior Service Credit
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Pension and other postretirement benefit plans, net loss and prior service credit included in AOCI	314	326
Other Postretirement Benefit Plan Prior Service Credit
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Pension and other postretirement benefit plans, net loss and prior service credit included in AOCI	375	383
Cumulative Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(1,954)	(2,355)	(2,186)
Other comprehensive income (loss) before reclassification adjustments, pretax	(84)	235	(150)
Tax	(139)	166	(19)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(223)	401	(169)
Reclassification adjustments, pretax	0	0	0
Tax	0	0	0
Reclassification adjustments, net of taxes	0	0	0
Other comprehensive income (loss), net of taxes	(223)	401	(169)
Adoption of ASU 2018-02 (see Note 2)	100
Adoption of new accounting standards (see Note 2)				0
Ending Balance	(2,077)	(1,954)	(2,355)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(4,910)	(5,226)	(4,148)
Other comprehensive income (loss) before reclassification adjustments, pretax	(692)	324	(1,177)
Tax	(24)	232	288
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(716)	556	(889)
Reclassification adjustments, pretax	424	(315)	(308)
Tax	(69)	75	119
Reclassification adjustments, net of taxes	355	(240)	(189)
Other comprehensive income (loss), net of taxes	(361)	316	(1,078)
Adoption of new accounting standards (see Note 2)				$ (8)
Ending Balance	$ (5,545)	$ (4,910)	$ (5,226)

Segment Reporting - Narrative (

Segment Reporting - Narrative (Details)	12 Months Ended
	Dec. 31, 2018segment
Segment Reporting [Abstract]
Number of operating segments	4

Segment Reporting - Sales of Co

Segment Reporting - Sales of Company's Products (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Sales	$ 42,294	$ 40,122	$ 39,807
Proceeds from sale of intangible assets	95	85	170
Operating Segments
Segment Reporting Information [Line Items]
Sales	42,151	39,662	39,014
Operating Segments | Pharmaceutical segment
Segment Reporting Information [Line Items]
Sales	37,689	35,390	35,151
Operating Segments | Pharmaceutical segment | Keytruda
Segment Reporting Information [Line Items]
Sales	7,171	3,809	1,402
Operating Segments | Pharmaceutical segment | Emend
Segment Reporting Information [Line Items]
Sales	522	556	549
Operating Segments | Pharmaceutical segment | Temodar
Segment Reporting Information [Line Items]
Sales	214	271	283
Operating Segments | Pharmaceutical segment | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	187	20	0
Operating Segments | Pharmaceutical segment | Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	149	0	0
Operating Segments | Pharmaceutical segment | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	3,151	2,308	2,173
Operating Segments | Pharmaceutical segment | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	1,798	1,676	1,640
Operating Segments | Pharmaceutical segment | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	907	821	641
Operating Segments | Pharmaceutical segment | RotaTeq
Segment Reporting Information [Line Items]
Sales	728	686	652
Operating Segments | Pharmaceutical segment | Zostavax
Segment Reporting Information [Line Items]
Sales	217	668	685
Operating Segments | Pharmaceutical segment | Bridion
Segment Reporting Information [Line Items]
Sales	917	704	482
Operating Segments | Pharmaceutical segment | Noxafil
Segment Reporting Information [Line Items]
Sales	742	636	595
Operating Segments | Pharmaceutical segment | Invanz
Segment Reporting Information [Line Items]
Sales	496	602	561
Operating Segments | Pharmaceutical segment | Cubicin
Segment Reporting Information [Line Items]
Sales	367	382	1,087
Operating Segments | Pharmaceutical segment | Cancidas
Segment Reporting Information [Line Items]
Sales	326	422	558
Operating Segments | Pharmaceutical segment | Primaxin
Segment Reporting Information [Line Items]
Sales	265	280	297
Operating Segments | Pharmaceutical segment | Simponi
Segment Reporting Information [Line Items]
Sales	893	819	766
Operating Segments | Pharmaceutical segment | Remicade
Segment Reporting Information [Line Items]
Sales	582	837	1,268
Operating Segments | Pharmaceutical segment | Belsomra
Segment Reporting Information [Line Items]
Sales	260	210	154
Operating Segments | Pharmaceutical segment | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	1,140	1,204	1,387
Operating Segments | Pharmaceutical segment | Zepatier
Segment Reporting Information [Line Items]
Sales	455	1,660	555
Operating Segments | Pharmaceutical segment | Zetia
Segment Reporting Information [Line Items]
Sales	857	1,344	2,560
Operating Segments | Pharmaceutical segment | Vytorin
Segment Reporting Information [Line Items]
Sales	497	751	1,141
Operating Segments | Pharmaceutical segment | Atozet
Segment Reporting Information [Line Items]
Sales	347	225	146
Operating Segments | Pharmaceutical segment | Adempas
Segment Reporting Information [Line Items]
Sales	329	300	169
Operating Segments | Pharmaceutical segment | Januvia
Segment Reporting Information [Line Items]
Sales	3,686	3,737	3,908
Operating Segments | Pharmaceutical segment | Janumet
Segment Reporting Information [Line Items]
Sales	2,228	2,158	2,201
Operating Segments | Pharmaceutical segment | NuvaRing
Segment Reporting Information [Line Items]
Sales	902	761	777
Operating Segments | Pharmaceutical segment | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	703	686	606
Operating Segments | Pharmaceutical segment | Singulair
Segment Reporting Information [Line Items]
Sales	708	732	915
Operating Segments | Pharmaceutical segment | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	453	484	511
Operating Segments | Pharmaceutical segment | Nasonex
Segment Reporting Information [Line Items]
Sales	376	387	537
Operating Segments | Pharmaceutical segment | Arcoxia
Segment Reporting Information [Line Items]
Sales	335	363	450
Operating Segments | Pharmaceutical segment | Follistim AQ
Segment Reporting Information [Line Items]
Sales	268	298	355
Operating Segments | Pharmaceutical segment | Dulera
Segment Reporting Information [Line Items]
Sales	214	287	436
Operating Segments | Pharmaceutical segment | Fosamax
Segment Reporting Information [Line Items]
Sales	209	241	284
Operating Segments | Pharmaceutical segment | Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	4,090	4,065	4,420
Operating Segments | Animal Health
Segment Reporting Information [Line Items]
Sales	4,212	3,875	3,478
Operating Segments | Animal Health | Livestock
Segment Reporting Information [Line Items]
Sales	2,630	2,484	2,287
Operating Segments | Animal Health | Companion Animals
Segment Reporting Information [Line Items]
Sales	1,582	1,391	1,191
Operating Segments | Other segments
Segment Reporting Information [Line Items]
Sales	250	397	385
Other
Segment Reporting Information [Line Items]
Sales	143	460	793
United States
Segment Reporting Information [Line Items]
Sales	18,212	17,424	18,478
United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	18,094	17,340	18,447
United States | Operating Segments | Pharmaceutical segment
Segment Reporting Information [Line Items]
Sales	16,608	15,854	17,073
United States | Operating Segments | Pharmaceutical segment | Keytruda
Segment Reporting Information [Line Items]
Sales	4,150	2,309	792
United States | Operating Segments | Pharmaceutical segment | Emend
Segment Reporting Information [Line Items]
Sales	312	342	356
United States | Operating Segments | Pharmaceutical segment | Temodar
Segment Reporting Information [Line Items]
Sales	6	16	15
United States | Operating Segments | Pharmaceutical segment | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	127	0	0
United States | Operating Segments | Pharmaceutical segment | Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	95	0	0
United States | Operating Segments | Pharmaceutical segment | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	1,873	1,565	1,780
United States | Operating Segments | Pharmaceutical segment | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	1,430	1,374	1,362
United States | Operating Segments | Pharmaceutical segment | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	627	581	447
United States | Operating Segments | Pharmaceutical segment | RotaTeq
Segment Reporting Information [Line Items]
Sales	496	481	482
United States | Operating Segments | Pharmaceutical segment | Zostavax
Segment Reporting Information [Line Items]
Sales	22	422	518
United States | Operating Segments | Pharmaceutical segment | Bridion
Segment Reporting Information [Line Items]
Sales	386	239	77
United States | Operating Segments | Pharmaceutical segment | Noxafil
Segment Reporting Information [Line Items]
Sales	353	309	284
United States | Operating Segments | Pharmaceutical segment | Invanz
Segment Reporting Information [Line Items]
Sales	253	361	329
United States | Operating Segments | Pharmaceutical segment | Cubicin
Segment Reporting Information [Line Items]
Sales	191	189	906
United States | Operating Segments | Pharmaceutical segment | Cancidas
Segment Reporting Information [Line Items]
Sales	12	20	25
United States | Operating Segments | Pharmaceutical segment | Primaxin
Segment Reporting Information [Line Items]
Sales	7	10	4
United States | Operating Segments | Pharmaceutical segment | Simponi
Segment Reporting Information [Line Items]
Sales	0	0	0
United States | Operating Segments | Pharmaceutical segment | Remicade
Segment Reporting Information [Line Items]
Sales	0	0	0
United States | Operating Segments | Pharmaceutical segment | Belsomra
Segment Reporting Information [Line Items]
Sales	96	98	84
United States | Operating Segments | Pharmaceutical segment | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	513	565	721
United States | Operating Segments | Pharmaceutical segment | Zepatier
Segment Reporting Information [Line Items]
Sales	8	771	488
United States | Operating Segments | Pharmaceutical segment | Zetia
Segment Reporting Information [Line Items]
Sales	45	352	1,588
United States | Operating Segments | Pharmaceutical segment | Vytorin
Segment Reporting Information [Line Items]
Sales	10	124	473
United States | Operating Segments | Pharmaceutical segment | Atozet
Segment Reporting Information [Line Items]
Sales	0	0	1
United States | Operating Segments | Pharmaceutical segment | Adempas
Segment Reporting Information [Line Items]
Sales	0	0	0
United States | Operating Segments | Pharmaceutical segment | Januvia
Segment Reporting Information [Line Items]
Sales	1,969	2,153	2,286
United States | Operating Segments | Pharmaceutical segment | Janumet
Segment Reporting Information [Line Items]
Sales	811	863	984
United States | Operating Segments | Pharmaceutical segment | NuvaRing
Segment Reporting Information [Line Items]
Sales	722	564	576
United States | Operating Segments | Pharmaceutical segment | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	495	496	420
United States | Operating Segments | Pharmaceutical segment | Singulair
Segment Reporting Information [Line Items]
Sales	20	40	40
United States | Operating Segments | Pharmaceutical segment | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	23	18	16
United States | Operating Segments | Pharmaceutical segment | Nasonex
Segment Reporting Information [Line Items]
Sales	23	54	184
United States | Operating Segments | Pharmaceutical segment | Arcoxia
Segment Reporting Information [Line Items]
Sales	0	0	0
United States | Operating Segments | Pharmaceutical segment | Follistim AQ
Segment Reporting Information [Line Items]
Sales	115	123	157
United States | Operating Segments | Pharmaceutical segment | Dulera
Segment Reporting Information [Line Items]
Sales	186	261	412
United States | Operating Segments | Pharmaceutical segment | Fosamax
Segment Reporting Information [Line Items]
Sales	4	6	5
United States | Operating Segments | Pharmaceutical segment | Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	1,228	1,148	1,261
United States | Operating Segments | Animal Health
Segment Reporting Information [Line Items]
Sales	1,238	1,090	989
United States | Operating Segments | Animal Health | Livestock
Segment Reporting Information [Line Items]
Sales	528	471	446
United States | Operating Segments | Animal Health | Companion Animals
Segment Reporting Information [Line Items]
Sales	710	619	543
United States | Operating Segments | Other segments
Segment Reporting Information [Line Items]
Sales	248	396	385
United States | Other
Segment Reporting Information [Line Items]
Sales	118	84	31
Int’l
Segment Reporting Information [Line Items]
Sales	24,083	22,698	21,329
Int’l | Operating Segments
Segment Reporting Information [Line Items]
Sales	24,057	22,322	20,566
Int’l | Operating Segments | Pharmaceutical segment
Segment Reporting Information [Line Items]
Sales	21,081	19,536	18,077
Int’l | Operating Segments | Pharmaceutical segment | Keytruda
Segment Reporting Information [Line Items]
Sales	3,021	1,500	610
Int’l | Operating Segments | Pharmaceutical segment | Emend
Segment Reporting Information [Line Items]
Sales	210	213	193
Int’l | Operating Segments | Pharmaceutical segment | Temodar
Segment Reporting Information [Line Items]
Sales	209	256	268
Int’l | Operating Segments | Pharmaceutical segment | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	61	20	0
Int’l | Operating Segments | Pharmaceutical segment | Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	54	0	0
Int’l | Operating Segments | Pharmaceutical segment | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	1,279	743	393
Int’l | Operating Segments | Pharmaceutical segment | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	368	303	279
Int’l | Operating Segments | Pharmaceutical segment | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	281	240	193
Int’l | Operating Segments | Pharmaceutical segment | RotaTeq
Segment Reporting Information [Line Items]
Sales	232	204	169
Int’l | Operating Segments | Pharmaceutical segment | Zostavax
Segment Reporting Information [Line Items]
Sales	195	246	168
Int’l | Operating Segments | Pharmaceutical segment | Bridion
Segment Reporting Information [Line Items]
Sales	531	465	405
Int’l | Operating Segments | Pharmaceutical segment | Noxafil
Segment Reporting Information [Line Items]
Sales	389	327	312
Int’l | Operating Segments | Pharmaceutical segment | Invanz
Segment Reporting Information [Line Items]
Sales	243	241	233
Int’l | Operating Segments | Pharmaceutical segment | Cubicin
Segment Reporting Information [Line Items]
Sales	176	193	181
Int’l | Operating Segments | Pharmaceutical segment | Cancidas
Segment Reporting Information [Line Items]
Sales	314	402	533
Int’l | Operating Segments | Pharmaceutical segment | Primaxin
Segment Reporting Information [Line Items]
Sales	258	270	293
Int’l | Operating Segments | Pharmaceutical segment | Simponi
Segment Reporting Information [Line Items]
Sales	893	819	766
Int’l | Operating Segments | Pharmaceutical segment | Remicade
Segment Reporting Information [Line Items]
Sales	582	837	1,268
Int’l | Operating Segments | Pharmaceutical segment | Belsomra
Segment Reporting Information [Line Items]
Sales	164	112	70
Int’l | Operating Segments | Pharmaceutical segment | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	627	639	666
Int’l | Operating Segments | Pharmaceutical segment | Zepatier
Segment Reporting Information [Line Items]
Sales	447	888	67
Int’l | Operating Segments | Pharmaceutical segment | Zetia
Segment Reporting Information [Line Items]
Sales	813	992	972
Int’l | Operating Segments | Pharmaceutical segment | Vytorin
Segment Reporting Information [Line Items]
Sales	487	627	668
Int’l | Operating Segments | Pharmaceutical segment | Atozet
Segment Reporting Information [Line Items]
Sales	347	225	146
Int’l | Operating Segments | Pharmaceutical segment | Adempas
Segment Reporting Information [Line Items]
Sales	329	300	169
Int’l | Operating Segments | Pharmaceutical segment | Januvia
Segment Reporting Information [Line Items]
Sales	1,718	1,584	1,622
Int’l | Operating Segments | Pharmaceutical segment | Janumet
Segment Reporting Information [Line Items]
Sales	1,417	1,296	1,217
Int’l | Operating Segments | Pharmaceutical segment | NuvaRing
Segment Reporting Information [Line Items]
Sales	180	197	202
Int’l | Operating Segments | Pharmaceutical segment | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	208	191	186
Int’l | Operating Segments | Pharmaceutical segment | Singulair
Segment Reporting Information [Line Items]
Sales	688	692	874
Int’l | Operating Segments | Pharmaceutical segment | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	431	466	494
Int’l | Operating Segments | Pharmaceutical segment | Nasonex
Segment Reporting Information [Line Items]
Sales	353	333	352
Int’l | Operating Segments | Pharmaceutical segment | Arcoxia
Segment Reporting Information [Line Items]
Sales	335	363	450
Int’l | Operating Segments | Pharmaceutical segment | Follistim AQ
Segment Reporting Information [Line Items]
Sales	153	174	197
Int’l | Operating Segments | Pharmaceutical segment | Dulera
Segment Reporting Information [Line Items]
Sales	28	26	24
Int’l | Operating Segments | Pharmaceutical segment | Fosamax
Segment Reporting Information [Line Items]
Sales	205	235	279
Int’l | Operating Segments | Pharmaceutical segment | Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	2,855	2,917	3,158
Int’l | Operating Segments | Animal Health
Segment Reporting Information [Line Items]
Sales	2,974	2,785	2,489
Int’l | Operating Segments | Animal Health | Livestock
Segment Reporting Information [Line Items]
Sales	2,102	2,013	1,841
Int’l | Operating Segments | Animal Health | Companion Animals
Segment Reporting Information [Line Items]
Sales	872	772	648
Int’l | Operating Segments | Other segments
Segment Reporting Information [Line Items]
Sales	2	1	0
Int’l | Other
Segment Reporting Information [Line Items]
Sales	$ 26	$ 376	$ 763

Segment Reporting - Consolidate

Segment Reporting - Consolidated Revenues by Geographic Area (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	$ 42,294	$ 40,122	$ 39,807
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	18,212	17,424	18,478
Europe, Middle East and Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	12,213	11,478	10,953
Japan
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	3,212	3,122	2,846
Asia Pacific (other than Japan and China)
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	2,909	2,751	2,483
Latin America
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	2,415	2,339	2,155
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	2,184	1,586	1,435
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	$ 1,149	$ 1,422	$ 1,457

Segment Reporting - Reconciliat

Segment Reporting - Reconciliation of Segment Profits to Income Before Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Interest income	$ 343	$ 385	$ 328
Interest expense	(772)	(754)	(693)
Depreciation and amortization	(4,519)	(4,676)	(5,471)
Research and development	(9,752)	(10,339)	(10,261)
Restructuring costs	(632)	(776)	(651)
Loss on extinguishment of debt		(191)
Charge related to the settlement of worldwide Keytruda patent litigation	0	0	(625)
Income Before Taxes	8,701	6,521	4,659
Total segment profits
Segment Reporting Information [Line Items]
Depreciation and amortization	(335)	(212)	(183)
Income Before Taxes	26,054	24,322	23,644
Total segment profits | Pharmaceutical segment
Segment Reporting Information [Line Items]
Depreciation and amortization	(243)	(125)	(160)
Income Before Taxes	24,292	22,495	22,141
Total segment profits | Animal Health
Segment Reporting Information [Line Items]
Depreciation and amortization	(82)	(75)	(10)
Income Before Taxes	1,659	1,552	1,357
Total segment profits | Other segments
Segment Reporting Information [Line Items]
Depreciation and amortization	(10)	(12)	(13)
Income Before Taxes	103	275	146
Other profits
Segment Reporting Information [Line Items]
Income Before Taxes	6	26	481
Unallocated
Segment Reporting Information [Line Items]
Interest income	343	385	328
Interest expense	(772)	(754)	(693)
Depreciation and amortization	(1,334)	(1,378)	(1,585)
Research and development	(8,853)	(9,481)	(9,218)
Amortization of purchase accounting adjustments	(2,664)	(3,056)	(3,692)
Restructuring costs	(632)	(776)	(651)
Charge related to termination of collaboration agreement with Samsung	(423)	0	0
Loss on extinguishment of debt	0	(191)	0
Gain on sale of certain migraine clinical development programs	0	0	100
Charge related to the settlement of worldwide Keytruda patent litigation	0	0	(625)
Other unallocated, net	$ (3,024)	$ (2,576)	$ (3,430)

Segment Reporting - Schedule of

Segment Reporting - Schedule of Equity Income from Affiliates and Depreciation and Amortization Included in Segment Profits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Depreciation and amortization	$ 4,519	$ 4,676	$ 5,471
Operating Segments
Segment Reporting Information [Line Items]
Equity (income) loss from affiliates	4	7	(105)
Depreciation and amortization	335	212	183
Operating Segments | Pharmaceutical
Segment Reporting Information [Line Items]
Equity (income) loss from affiliates	4	7	(105)
Depreciation and amortization	243	125	160
Operating Segments | Animal Health
Segment Reporting Information [Line Items]
Equity (income) loss from affiliates	0	0	0
Depreciation and amortization	82	75	10
Operating Segments | All Other
Segment Reporting Information [Line Items]
Equity (income) loss from affiliates	0	0	0
Depreciation and amortization	$ 10	$ 12	$ 13

Segment Reporting - Property, P

Segment Reporting - Property, Plant and Equipment, Net by Geographic Area (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net	$ 13,291	$ 12,439	$ 12,026
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net	8,306	8,070	8,114
Europe, Middle East and Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net	3,706	3,151	2,732
Asia Pacific (other than Japan and China)
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net	684	632	623
Latin America
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net	264	271	234
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net	167	150	152
Japan
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net	159	158	164
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net	$ 5	$ 7	$ 7