Merck & Co. (MRK) 10-Q 8 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	MRK
Entity Registrant Name	Merck & Co., Inc.
Entity Central Index Key	310,158
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		2,690,303,898

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENT OF INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Sales	$ 10,037	$ 9,434
Costs, Expenses and Other
Materials and production	3,184	3,049
Marketing and administrative	2,508	2,472
Research and development	3,196	1,830
Restructuring costs	95	151
Other (income) expense, net	(291)	(71)
Total Costs, Expenses and Other	8,692	7,431
Income Before Taxes	1,345	2,003
Taxes on Income	604	447
Net Income	741	1,556
Less: Net Income Attributable to Noncontrolling Interests	5	5
Net Income Attributable to Merck & Co., Inc.	$ 736	$ 1,551
Basic Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 0.27	$ 0.56
Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	0.27	0.56
Dividends Declared per Common Share (in dollars per share)	$ 0.48	$ 0.47

CONDENSED CONSOLIDATED STATEME3

CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net Income Attributable to Merck & Co., Inc.	$ 736	$ 1,551
Other Comprehensive Income (Loss) Net of Taxes:
Net unrealized loss on derivatives, net of reclassifications	(70)	(232)
Net unrealized (loss) gain on investments, net of reclassifications	(99)	43
Benefit plan net gain (loss) and prior service credit (cost), net of amortization	36	26
Cumulative translation adjustment	257	309
Other comprehensive income (loss), net of taxes	124	146
Comprehensive Income Attributable to Merck & Co., Inc.	$ 860	$ 1,697

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEET - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Current Assets
Cash and cash equivalents	$ 4,483	$ 6,092
Short-term investments	2,863	2,406
Accounts receivable (net of allowance for doubtful accounts of $205 in 2018 and $210 in 2017)	7,245	6,873
Inventories (excludes inventories of $1,136 in 2018 and $1,187 in 2017 classified in Other assets - see Note 7)	5,382	5,096
Other current assets	4,112	4,299
Total current assets	24,085	24,766
Investments	11,033	12,125
Property, Plant and Equipment, at cost, net of accumulated depreciation of $16,483 in 2018 and $16,602 in 2017	12,561	12,439
Goodwill	18,304	18,284
Other Intangibles, Net	13,500	14,183
Other Assets	6,558	6,075
Total Assets	86,041	87,872
Current Liabilities
Loans payable and current portion of long-term debt	2,055	3,057
Trade accounts payable	3,162	3,102
Accrued and other current liabilities	9,709	10,427
Income taxes payable	717	708
Dividends payable	1,317	1,320
Total current liabilities	16,960	18,614
Long-Term Debt	21,501	21,353
Deferred Income Taxes	2,206	2,219
Other Noncurrent Liabilities	11,473	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	39,874	39,902
Retained earnings	41,107	41,350
Accumulated other comprehensive loss	(5,060)	(4,910)
Stockholders' equity before deduction for treasury stock	77,709	78,130
Less treasury stock, at cost: 884,622,139 shares in 2018 and 880,491,914 shares in 2017	44,041	43,794
Total Merck & Co., Inc. stockholders’ equity	33,668	34,336
Noncontrolling Interests	233	233
Total equity	33,901	34,569
Liabilities and Equity	$ 86,041	$ 87,872

CONDENSED CONSOLIDATED BALANCE5

CONDENSED CONSOLIDATED BALANCE SHEET (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 205	$ 210
Inventories classified in Other assets	1,136	1,187
Accumulated depreciation	$ 16,483	$ 16,602
Common stock, par value (in dollars per share)	$ 0.50	$ 0.50
Common stock, shares authorized (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 (shares)	884,622,139	880,491,914

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flows from Operating Activities
Net income	$ 741	$ 1,556
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	1,137	1,193
Intangible asset impairment charges	0	80
Charge for future payments related to Eisai collaboration license options	650	0
Deferred income taxes	(30)	(54)
Share-based compensation	80	74
Other	50	(28)
Net changes in assets and liabilities	(1,473)	(2,535)
Net Cash Provided by Operating Activities	1,155	286
Cash Flows from Investing Activities
Capital expenditures	(450)	(339)
Purchases of securities and other investments	(1,326)	(2,929)
Proceeds from sales of securities and other investments	1,848	6,819
Acquisitions of businesses, net of cash acquired	0	(306)
Other	(269)	(52)
Net Cash (Used in) Provided by Investing Activities	(197)	3,193
Cash Flows from Financing Activities
Net change in short-term borrowings	(1)	3,784
Payments on debt	(1,003)	(300)
Purchases of treasury stock	(566)	(1,019)
Dividends paid to stockholders	(1,299)	(1,294)
Proceeds from exercise of stock options	230	313
Other	(83)	(23)
Net Cash (Used in) Provided by Financing Activities	(2,722)	1,461
Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	154	253
Net (Decrease) Increase in Cash, Cash Equivalents and Restricted Cash	(1,610)	5,193
Cash, Cash Equivalents and Restricted Cash at Beginning of Year (includes restricted cash of $4 million at January 1, 2018 included in Other Assets)	6,096	6,515
Cash, Cash Equivalents and Restricted Cash at Beginning of Year (includes restricted cash of $4 million at January 1, 2018 included in Other Assets)	$ 4,486	$ 11,708

CONDENSED CONSOLIDATED STATEME7

CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Statement of Cash Flows [Abstract]
Restricted cash	$ 3	$ 4

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of Merck & Co., Inc. (Merck or the Company) have been prepared pursuant to the rules and regulations for reporting on Form 10-Q. Accordingly, certain information and disclosures required by accounting principles generally accepted in the United States for complete consolidated financial statements are not included herein. These interim statements should be read in conjunction with the audited financial statements and notes thereto included in Merck’s Form 10-K filed on February 27, 2018. The results of operations of any interim period are not necessarily indicative of the results of operations for the full year. In the Company’s opinion, all adjustments necessary for a fair statement of these interim statements have been included and are of a normal and recurring nature. Certain reclassifications have been made to prior year amounts to conform to the current 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 will be applied 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 . See Note 2 for additional information related to the adoption of this standard. 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, less impairment, adjusted for subsequent observable price changes, 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 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 (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 these amounts 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 provisional amount of $266 million with a corresponding increase to Retained earnings (see Note 15). The Company’s policy for releasing the disproportionate income tax effects from Accumulated other comprehensive loss is to utilize the item-by-item approach. The impact of adopting the above standards is as follows: ($ 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 - Debit (Credit) Accounts receivable $ 5 $ 5 Liabilities - Credit (Debit) Income Taxes Payable (3 ) (3 ) Debt 14 14 Deferred Income Taxes (54 ) (54 ) Equity - Credit (Debit) Retained earnings 5 8 54 (11 ) 266 322 Accumulated other comprehensive loss (8 ) (266 ) (274 ) In March 2017, the FASB amended the guidance 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 to adopt the requirement for separate presentation in the income statement of service costs and other components and a prospective transition method to adopt 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 was reclassified to Other (income) expense, net from the previous classification within Materials and production costs, Marketing and administrative expenses and Research and development costs (see Note 12). 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 prior year period 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. Recently Issued Accounting Standards Not Yet Adopted In February 2016, the FASB issued new accounting guidance for the accounting and reporting of leases. 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 guidance will be effective for interim and annual periods beginning in 2019 and will be adopted using a modified retrospective approach. The Company intends to elect available practical expedients. The Company is currently evaluating the impact of adoption on its consolidated financial statements. 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 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 new guidance is effective for interim and annual periods in 2020. Early adoption is permitted. The Company does not anticipate that the adoption of the new guidance will have a material effect on its consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies 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 Note 1). 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 provides principles that an entity applies to report useful information about the amount, timing, and uncertainty of revenue and cash flows arising from its contracts to provide goods or services to customers. The core principle 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. The Company’s significant accounting policies are detailed in Note 2 to the consolidated financial statements included in Merck’s Annual Report on Form 10-K for the year ended December 31, 2017. Changes to the Company’s revenue recognition policy as a result of adopting ASC 606 are described below. See Note 16 for disaggregated revenue disclosures. Revenue Recognition — 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. 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. Merck’s payment terms for U.S. customers are typically net 36 days from receipt of invoice; however, certain products 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 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 also used for certain types of variable consideration. 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 provision for aggregate customer discounts covers chargebacks and rebates. Chargebacks are discounts that occur when a contracted customer purchases directly 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. These discounts, in the aggregate, reduced U.S. sales by $2.4 billion and $2.5 billion in the first quarter of 2018 and 2017 , respectively. Outside of the United States, variable consideration in the form of discounts and rebates are a combination of commercially-driven discounts in highly competitive product classes, discounts required to gain or maintain reimbursement, or legislatively mandated rebates. In certain European countries, legislatively mandated rebates are calculated based on an estimate of the government’s total unbudgeted spending and the Company’s specific payback obligation. Rebates may also be required based on specific product sales thresholds. In all cases, the Company applies an estimated factor against its actual invoiced sales to represent the expected level of future discount or rebate obligation associated with the sale. The Company maintains a returns policy that allows its U.S. pharmaceutical customers to return product within a specified period prior to and subsequent to the expiration date (generally, three to six months before and 12 months after product expiration). The estimate of the provision for returns is based upon historical experience with actual returns. Additionally, the Company considers factors such as levels of inventory in the distribution channel, product dating and expiration period, whether products have been discontinued, entrance in the market of generic competition, changes in formularies or launch of over-the-counter products, among others. Outside of the United States, returns are only allowed on a limited basis in certain countries. The following table provides the effects of adopting ASC 606 on the Consolidated Statement of Income in the first quarter of 2018: Three Months Ended March 31, 2018 ($ in millions) As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Sales $ 10,037 $ (24 ) $ 10,013 Materials and production 3,184 (11 ) 3,173 Income before taxes 1,345 (13 ) 1,332 Taxes on income 604 (2 ) 602 Net income attributable to Merck & Co., Inc. 736 (11 ) 725 The following table provides the effects of adopting ASC 606 on the consolidated balance sheet as of March 31, 2018: March 31, 2018 ($ in millions) As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Assets Accounts receivable $ 7,245 $ (36 ) $ 7,209 Inventories 5,382 13 5,395 Liabilities Accrued and other current liabilities 9,709 (3 ) 9,706 Income taxes payable 717 (4 ) 713 Equity Retained earnings 41,107 (16 ) 41,091

Acquisitions, Research Collabor

Acquisitions, Research Collaborations and License Agreements	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
Acquisitions, Research Collaborations and License Agreements	Acquisitions, 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. In March 2018, Merck and Eisai Co., Ltd. (Eisai) announced a strategic collaboration for the worldwide co-development and co-commercialization of Lenvima (lenvatinib mesylate), 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 (pembrolizumab). Eisai will record Lenvima product sales globally, as monotherapy and in combination, and Merck and Eisai will share gross profits equally. Merck will record its share of product sales of Lenvima, net of cost of sales and commercialization costs, as alliance revenue. Expenses incurred during co-development, including for studies evaluating Lenvima as monotherapy, will be shared equally by the two companies. Under the agreement, Merck made upfront payments to Eisai of $750 million and will make payments of up to $650 million for certain option rights through 2021 ( $325 million in January 2019 or earlier in certain circumstances, $200 million in January 2020 and $125 million in January 2021). The Company recorded an aggregate charge of $1.4 billion in Research and development expenses in the first quarter of 2018 related to the upfront payments and future option payments. In addition, Eisai is eligible to receive up to $385 million in the future 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 February 2018, Merck and Viralytics Limited (Viralytics) announced a definitive agreement pursuant to which Merck will acquire Viralytics, an Australian publicly traded company focused on oncolytic immunotherapy treatments for a range of cancers, for AUD 1.75 per share. The proposed acquisition values the total issued shares in Viralytics at approximately AUD 502 million ( $394 million ). Upon completion of the transaction, Merck will gain full rights to Cavatak (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 remains subject to a Viralytics shareholder vote and customary regulatory approvals. Merck anticipates the transaction will close in the second quarter of 2018. 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 noncontrolling interest related to Vallée.

Collaborative Arrangements

Collaborative Arrangements	3 Months Ended
	Mar. 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 PLC (AstraZeneca) entered into a global strategic oncology collaboration to co-develop and co-commercialize AstraZeneca’s Lynparza (olaparib) 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 (pembrolizumab) and Imfinzi (durvalumab). 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 including thyroid cancer. 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 is recording its share of product sales of Lynparza, net of costs 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 is making payments of $750 million over a multi-year period for certain license options ( $250 million of which was paid in 2017). 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 options payments. In addition, the agreement provides for additional payments from Merck to AstraZeneca of up to an additional $6.15 billion contingent upon successful achievement of regulatory milestones of $2.05 billion and sales-based milestones of $4.1 billion for total aggregate consideration of up to $8.5 billion . In the first quarter of 2018, Merck determined it was probable that annual sales of Lynparza in the future would trigger a $150 million sales-based milestone payment from Merck to AstraZeneca upon achievement of the sales milestone. Accordingly, in the first quarter of 2018, Merck recorded a $150 million liability and a corresponding intangible asset and also recognized $9 million of cumulative amortization expense within Materials and production costs. Merck previously accrued a $100 million sales-based milestone in 2017. The remaining $3.85 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 January 2018, Lynparza received approval in the United States for the treatment of certain patients with metastatic breast cancer, triggering a $70 million milestone payment from Merck to AstraZeneca. This milestone payment was capitalized and will be amortized over the remaining useful life of Lynparza. Potential future regulatory milestone payments of $1.98 billion remain under the agreement. Summarized information related to this collaboration is as follows: Three Months Ended ($ in millions) 2018 Alliance revenues (net of commercialization costs) $ 33 Materials and production (1) 12 Marketing and administrative 7 Research and development 29 Receivables from AstraZeneca 31 Payables to AstraZeneca 783 (1) Includes amortization of intangible assets. 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 (riociguat), which is approved to treat pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. The two companies equally share costs and profits from the collaboration and 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. In 2017, annual sales of Adempas exceeded $500 million triggering a $350 million milestone payment from Merck to Bayer, which was accrued for in 2016 when Merck deemed the payment to be probable. The milestone was paid in the first quarter of 2018. There are $775 million of additional potential future sales-based milestone payments that have not yet been accrued as they are not deemed by the Company to be probable at this time. Summarized information related to this collaboration is as follows: Three Months Ended ($ in millions) 2018 2017 Net product sales recorded by Merck $ 43 $ 31 Merck’s profit share from sales in Bayer's marketing territories 25 53 Total sales 68 84 Materials and production (1) 27 23 Marketing and administrative 8 7 Research and development 32 22 Receivables from Bayer 35 Payables to Bayer — (1) Includes amortization of intangible assets.

Restructuring

Restructuring	3 Months Ended
	Mar. 31, 2018
Restructuring and Related Activities [Abstract]
Restructuring	Restructuring The Company incurs substantial costs for restructuring program activities related to Merck’s productivity and cost reduction initiatives, as well as in connection with the integration of certain acquired businesses. 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 $104 million and $215 million in the first quarter of 2018 and 2017 , respectively, related to restructuring program activities. Since inception of the programs through March 31, 2018 , Merck has recorded total pretax accumulated costs of approximately $13.6 billion and eliminated approximately 44,060 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. While the Company has substantially completed the actions under these programs, approximately $500 million of pretax costs are expected to be incurred in 2018 relating to anticipated employee separations and remaining asset-related costs. For segment reporting, restructuring charges are unallocated expenses. The following tables summarize the charges related to restructuring program activities by type of cost: Three Months Ended March 31, 2018 ($ in millions) Separation Costs Accelerated Depreciation Other Total Materials and production $ — $ — $ 6 $ 6 Marketing and administrative — 1 — 1 Research and development — (3 ) 5 2 Restructuring costs 55 — 40 95 $ 55 $ (2 ) $ 51 $ 104 Three Months Ended March 31, 2017 ($ in millions) Separation Costs Accelerated Depreciation Other Total Materials and production $ — $ 51 $ 12 $ 63 Marketing and administrative — — 1 1 Research and development — (2 ) 2 — Restructuring costs 84 — 67 151 $ 84 $ 49 $ 82 $ 215 Separation costs are associated with actual headcount reductions, as well as those headcount reductions which were probable and could be reasonably estimated. In the first quarter of 2018 and 2017 , approximately 710 positions and 545 positions, respectively, were eliminated under restructuring program activities. 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 of 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 and 2017 includes asset abandonment, shut-down and other related costs, as well as pretax gains and losses resulting from sales of facilities and related assets. Additionally, other activity includes certain employee-related costs associated with pension and other postretirement benefit plans (see Note 11) and share-based compensation. The following table summarizes the charges and spending relating to restructuring program activities for the three months ended March 31, 2018 : ($ in millions) Separation Costs Accelerated Depreciation Other Total Restructuring reserves January 1, 2018 $ 619 $ — $ 128 $ 747 Expense 55 (2 ) 51 104 (Payments) receipts, net (139 ) — (64 ) (203 ) Non-cash activity — 2 1 3 Restructuring reserves March 31, 2018 (1) $ 535 $ — $ 116 $ 651 (1) The remaining cash outlays are expected to be substantially completed by the end of 2020.

Financial Instruments

Financial Instruments	3 Months Ended
	Mar. 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 Condensed Consolidated Balance Sheet. Changes in the fair value of derivative contracts are recorded each period in either current earnings or Other comprehensive income ( 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 Accumulated other comprehensive income ( 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 Condensed 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 Condensed 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 1), 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 Condensed 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 effect of the Company’s net investment hedges on OCI and the Consolidated Statement of Income is shown below: Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income (1) Location of Pretax (Gain) Loss Recognized in Income For Amounts Excluded from Effectiveness Testing Amount of Pretax (Gain) Loss Recognized in Income For Amounts Excluded from Effectiveness Testing Three Months Ended March 31, Three Months Ended March 31, ($ in millions) 2018 2017 2018 2017 Net Investment Hedging Relationships Foreign exchange contracts $ (2 ) $ — Other (income) expense, net $ — $ — Euro-denominated notes 178 135 Other (income) expense, net — — (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. At March 31, 2018 , the Company was a party to 26 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. ($ in millions) March 31, 2018 Debt Instrument Par Value of Debt Number of Interest Rate Swaps Held Total Swap Notional Amount 1.30% notes due 2018 $ 1,000 4 $ 1,000 5.00% notes due 2019 1,250 3 550 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 Condensed 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: Carrying Amount of Hedged Assets (Liabilities) Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount ($ in millions) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Balance Sheet Line Item in which Hedged Item is Included Loans payable and current portion of long-term debt $ (998 ) $ (983 ) $ 2 $ 17 Long-Term Debt (1) (5,083 ) (5,146 ) 106 41 (1) Amounts include hedging adjustment gains related to discontinued hedging relationships of $9 million and $11 million at March 31, 2018 and December 31, 2017, respectively. Presented in the table below is the fair value of derivatives on a gross basis segregated between those derivatives that are designated as hedging instruments and those that are not designated as hedging instruments: March 31, 2018 December 31, 2017 Fair Value of Derivative U.S. Dollar Notional Fair Value of Derivative U.S. Dollar Notional ($ in millions) 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 — 1 1,000 — 3 1,000 Interest rate swap contracts Other noncurrent liabilities — 114 5,200 — 52 4,650 Foreign exchange contracts Other current assets 21 — 3,584 51 — 4,216 Foreign exchange contracts Other assets 30 — 2,407 38 — 1,936 Foreign exchange contracts Accrued and other current liabilities — 119 3,205 — 71 2,014 Foreign exchange contracts Other noncurrent liabilities — 1 56 — 1 20 $ 51 $ 235 $ 15,452 $ 91 $ 127 $ 14,386 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts Other current assets $ 58 $ — $ 5,434 $ 39 $ — $ 3,778 Foreign exchange contracts Accrued and other current liabilities — 89 6,764 — 90 7,431 $ 58 $ 89 $ 12,198 $ 39 $ 90 $ 11,209 $ 109 $ 324 $ 27,650 $ 130 $ 217 $ 25,595 As noted above, the Company records its derivatives on a gross basis in the Condensed 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: March 31, 2018 December 31, 2017 ($ in millions) Asset Liability Asset Liability Gross amounts recognized in the consolidated balance sheet $ 109 $ 324 $ 130 $ 217 Gross amount subject to offset in master netting arrangements not offset in the consolidated balance sheet (103 ) (103 ) (94 ) (94 ) Cash collateral received — — (3 ) — Net amounts $ 6 $ 221 $ 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: Three Months Ended Three Months Ended ($ in millions) Sales Other (income) expense, net (1) Other comprehensive income (loss) Sales Other (income) expense, net (1) Other comprehensive income (loss) Financial Statement Line Items in which Effects of Fair Value or Cash Flow Hedges are Recorded $ 10,037 $ (291 ) $ 124 $ 9,434 $ (71 ) $ 146 (Gain) loss on fair value hedging relationships Interest rate swap contracts Hedged items — (62 ) — — (16 ) — Derivatives designated as hedging instruments — 62 — — 4 — Impact of cash flow hedging relationships Foreign exchange contracts Amount of (loss) recognized in OCI on derivatives — — (181 ) — — (263 ) (Decrease) increase in Sales as a result of AOCI reclassifications (93 ) — 93 94 — (94 ) (1) Interest expense is a component of Other (income) expense, net. The table below provides information regarding the income statements effects of derivatives not designated as hedging instruments: Amount of Derivative Pretax (Gain) Loss Recognized in Income Location of Derivative Pretax (Gain) Loss Recognized in Income Three Months Ended March 31, ($ in millions) 2018 2017 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts (1) Other (income) expense, net $ 28 $ (47 ) Foreign exchange contracts (2) Sales 8 — (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 March 31, 2018 , the Company estimates $264 million of pretax net unrealized losses on derivatives maturing within the next 12 months that hedge foreign currency denominated sales over that same period will be reclassified from AOCI to Sales . The amount ultimately reclassified to Sales may differ as foreign exchange rates change. Realized gains and losses are ultimately determined by actual exchange rates at maturity. Investments in Debt and Equity Securities Information on investments in debt and equity securities is as follows: March 31, 2018 December 31, 2017 Fair Value Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized ($ in millions) Gains Losses Gains Losses Corporate notes and bonds $ 9,860 $ 9,978 $ 3 $ (121 ) $ 9,806 $ 9,837 $ 9 $ (40 ) U.S. government and agency securities 1,810 1,833 — (23 ) 2,042 2,059 — (17 ) Asset-backed securities 1,569 1,585 1 (17 ) 1,542 1,548 1 (7 ) Foreign government bonds 759 769 — (10 ) 733 739 — (6 ) Commercial paper 130 130 — — 159 159 — — Mortgage-backed securities 78 79 — (1 ) 626 634 1 (9 ) Total debt securities $ 14,206 $ 14,374 $ 4 $ (172 ) $ 14,908 $ 14,976 $ 11 $ (79 ) Publicly traded equity securities (1) 332 275 265 16 (6 ) Total debt and publicly traded equity securities $ 14,538 $ 15,183 $ 15,241 $ 27 $ (85 ) (1) Pursuant to the adoption of ASU 2016-01 (see Note 1), beginning on January 1, 2018, changes in the fair value of publicly traded equity securities are recognized in net income. Unrealized net gains of $44 million were recognized during the first quarter of 2018 on equity securities still held at March 31, 2018. At March 31 2018, the Company also had $516 million of equity investments without readily determinable fair values included in Other Assets . During the first quarter of 2018, the Company recognized unrealized gains of $33 million on certain of these equity investments recorded in Other (income) expense, net based on observable price changes from transactions involving similar investments of the same investee. In addition, during the first quarter of 2018, the Company recognized impairment losses of $8 million related to certain of these investments. Available-for-sale debt securities included in Short-term investments totaled $2.9 billion at March 31, 2018 . Of the remaining debt securities, $10.6 billion mature within five years. At March 31, 2018 and December 31, 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 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 ($ in millions) March 31, 2018 December 31, 2017 Assets Investments Corporate notes and bonds $ — $ 9,741 $ — $ 9,741 $ — $ 9,678 $ — $ 9,678 U.S. government and agency securities — 1,585 — 1,585 68 1,767 — 1,835 Asset-backed securities (1) — 1,517 — 1,517 — 1,476 — 1,476 Foreign government bonds — 759 — 759 — 732 — 732 Commercial paper — 130 — 130 — 159 — 159 Mortgage-backed securities — — — — — 547 — 547 Publicly traded equity securities 164 — — 164 104 — — 104 164 13,732 — 13,896 172 14,359 — 14,531 Other assets (2) U.S. government and agency securities 64 161 — 225 — 207 — 207 Corporate notes and bonds — 119 — 119 — 128 — 128 Mortgage-backed securities — 78 — 78 — 79 — 79 Asset-backed securities (1) — 52 — 52 — 66 — 66 Foreign government bonds — — — — — 1 — 1 Publicly traded equity securities 168 — — 168 171 — — 171 232 410 — 642 171 481 — 652 Derivative assets (3) Purchased currency options — 46 — 46 — 80 — 80 Forward exchange contracts — 63 — 63 — 48 — 48 Interest rate swaps — — — — — 2 — 2 — 109 — 109 — 130 — 130 Total assets $ 396 $ 14,251 $ — $ 14,647 $ 343 $ 14,970 $ — $ 15,313 Liabilities Other liabilities Contingent consideration $ — $ — $ 919 $ 919 $ — $ — $ 935 $ 935 Derivative liabilities (3) Forward exchange contracts — 208 — 208 — 162 — 162 Interest rate swaps — 115 — 115 — 55 — 55 Written currency options — 1 — 1 — — — — — 324 — 324 — 217 — 217 Total liabilities $ — $ 324 $ 919 $ 1,243 $ — $ 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 the first three months of 2018 . As of March 31, 2018 , Cash and cash equivalents of $4.5 billion included $3.5 billion of cash equivalents (which would be considered Level 2 in the fair value hierarchy). Contingent Consideration Summarized information about the changes in liabilities for contingent consideration is as follows: Three Months Ended March 31, ($ in millions) 2018 2017 Fair value January 1 $ 935 $ 891 Changes in fair value (1) 36 34 Additions 8 — Payments (60 ) — Fair value March 31 (2) $ 919 $ 925 (1) Recorded in Research and development expenses, Materials and production costs and Other (income) expense, net . Includes cumulative translation adjustments. (2) Includes $337 million recorded as a current liability for amounts expected to be paid within the next 12 months. The payments of contingent consideration in the first quarter of 2018 relate to liabilities recorded in connection with the 2016 termination of the Sanofi Pasteur MSD joint venture. 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 March 31, 2018 , was $24.3 billion compared with a carrying value of $23.6 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. At March 31, 2018 , the Company’s total net accounts receivable outstanding for more than one year were approximately $80 million . The Company does not expect to have write-offs or adjustments to accounts receivable which would have a material adverse effect on its financial position, liquidity or results of operations. 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. As of March 31, 2018 , the Company had not received any cash collateral. At December 31, 2017 , the Company had received cash collateral of $3 million from various counterparties and the obligation to return such collateral is recorded in Accrued and other current liabilities . The Company had not advanced any cash collateral to counterparties as of March 31, 2018 or December 31, 2017 .

Inventories

Inventories	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories consisted of: ($ in millions) March 31, 2018 December 31, 2017 Finished goods $ 1,530 $ 1,334 Raw materials and work in process 4,764 4,703 Supplies 199 201 Total (approximates current cost) 6,493 6,238 Increase to LIFO costs 25 45 $ 6,518 $ 6,283 Recognized as: Inventories $ 5,382 $ 5,096 Other assets 1,136 1,187 Amounts recognized as Other assets are comprised almost entirely of raw materials and work in process inventories. At March 31, 2018 and December 31, 2017 , these amounts included $1.1 billion of inventories not expected to be sold within one year. In addition, these amounts included $18 million and $80 million at March 31, 2018 and December 31, 2017 , respectively, of inventories produced in preparation for product launches.

Contingencies

Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies 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 March 31, 2018 , approximately 4,040 cases are filed and pending against Merck in either federal or state court. In approximately 10 of these actions, plaintiffs allege, among other things, that they have suffered osteonecrosis of the jaw (ONJ), generally subsequent to invasive dental procedures, such as tooth extraction or dental implants and/or delayed healing, in association with the use of Fosamax . In addition, plaintiffs in approximately 4,030 of these actions generally allege that they sustained femur fractures and/or other bone injuries (Femur Fractures) in association with the use of Fosamax . Cases Alleging ONJ and/or Other Jaw Related Injuries In August 2006, the Judicial Panel on Multidistrict Litigation (JPML) ordered that certain Fosamax product liability cases pending in federal courts nationwide should be transferred and consolidated into one multidistrict litigation ( Fosamax ONJ MDL) for coordinated pre-trial proceedings. In 2014, Merck settled approximately 95% of the ONJ cases pending in the Fosamax ONJ MDL and in state courts for a payment of $27.3 million . The escrow agent under the agreement has been making settlement payments to qualifying plaintiffs. The ONJ Master Settlement Agreement has no effect on the cases alleging Femur Fractures discussed below. Discovery is currently ongoing in some of the approximately 10 remaining ONJ cases that are pending in various federal and state courts and the Company intends to defend against these lawsuits. Cases Alleging Femur Fractures In March 2011, Merck submitted a Motion to Transfer to the 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). The Femur Fracture MDL court also dismissed without prejudice another approximately 510 cases pending plaintiffs’ appeal of the preemption ruling to the 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. In addition, in June 2014, the Femur Fracture MDL court granted Merck summary judgment in the Gaynor v. Merck case and found that Merck’s updates in January 2011 to the Fosamax label regarding atypical femur fractures were adequate as a matter of law and that Merck adequately communicated those changes. The plaintiffs in Gaynor did not appeal the Femur Fracture MDL court’s findings with respect to the adequacy of the 2011 label change but did appeal the dismissal of their case based on preemption grounds, and the Third Circuit subsequently reversed that dismissal in its March 2017 decision. In August 2014, Merck filed a motion requesting that the Femur Fracture MDL court enter a further order requiring all plaintiffs in the Femur Fracture MDL who claim that the 2011 Fosamax label is inadequate and the proximate cause of their alleged injuries to show cause why their cases should not be dismissed based on the court’s preemption decision and its ruling in the Gaynor case. In November 2014, the court granted Merck’s motion and entered the requested show cause order. No plaintiffs responded to or appealed the November 2014 show cause order. As of March 31, 2018 , approximately 540 cases were pending in the Femur Fracture MDL following the reinstatement of the cases that had been on appeal to the Third Circuit. The 510 cases dismissed without prejudice that were also pending the final resolution of the aforementioned appeal have not yet been reinstated. As of March 31, 2018 , approximately 2,700 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 March 31, 2018 , approximately 280 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. Oral argument on plaintiff’s appeal in Galper was held in November 2016 and, 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 March 31, 2018 , Merck is aware of approximately 1,245 product user claims alleging generally that use of Januvia and/or Janumet caused the development of pancreatic cancer and other injuries. These complaints were filed in several different state and federal courts. Most of the claims were filed in a consolidated multidistrict litigation proceeding in the U.S. District Court for the Southern District of California called “In re Incretin-Based Therapies Products Liability Litigation” (MDL). The MDL includes federal lawsuits alleging pancreatic cancer due to use of the following medicines: Januvia, Janumet , Byetta and Victoza, the latter two of which are products manufactured by other pharmaceutical companies. The majority of claims not filed in the MDL were filed in 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 preemption. Of the approximately 1,245 product user claims, these rulings resulted in the dismissal of approximately 1,100 product user claims. Plaintiffs appealed the MDL and California State Court preemption rulings. In November 2017, the U.S. Court of Appeals for the Ninth Circuit (Ninth Circuit) reversed the trial court’s ruling in the MDL and remanded for further proceedings. The Ninth Circuit did not address the substance of defendants’ preemption argument but instead ruled that the district court made various errors during discovery. Jurisdiction returned to U.S. District Court for the Southern District of California on January 2, 2018. The preemption appeal in the California state court litigation has been fully briefed, but the court has not yet scheduled oral argument. On March 21, 2018, the district court in the MDL entered a case management order setting forth a schedule for completing discovery on general causation and preemption issues and for renewing summary judgment and Daubert motions. The filing deadline for Daubert and summary judgment motions is set for December 11, 2018. As of March 31, 2018 , seven product users have claims pending against Merck in state courts other than California state court, including four active product user claims pending in Illinois state court. In June 2017, the Illinois trial court denied Merck’s motion for summary judgment on grounds of preemption. Merck sought permission to appeal that order on an interlocutory basis and was granted a stay of proceedings in the trial court. In September 2017, an intermediate appellate court in Illinois denied Merck’s petition for interlocutory review. Merck filed a petition for review with the Illinois Supreme Court and, on January 18, 2018, the Illinois Supreme Court directed the appellate court to answer the certified question. Briefing is expected to occur in the second quarter of 2018. Proceedings in the trial court remain stayed. 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. Propecia/Proscar As previously disclosed, Merck is a defendant in product liability lawsuits in the United States involving Propecia and/or Proscar . As of March 31, 2018 , there were approximately 600 active lawsuits filed by plaintiffs who allege that they have experienced persistent sexual side effects following cessation of treatment with Propecia and/or Proscar . Approximately 15 of the plaintiffs also allege that Propecia or Proscar has caused or can cause prostate cancer, testicular cancer or male breast cancer. The lawsuits have been filed in various federal courts and in state court in New Jersey. The federal lawsuits have been 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 have been consolidated before Judge Hyland in Middlesex County (NJ Coordinated Proceedings). In addition, there is one matter pending in state court in California, one matter pending in state court in Ohio, and one matter pending in state court in Massachusetts. On April 9, 2018, Merck and the Plaintiffs’ Executive Committee in the 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 is subject to certain contingencies, including 95% plaintiff participation and a per plaintiff clawback if the participation rate is less than 100% . The Company intends to defend against any remaining unsettled lawsuits. Governmental Proceedings As previously disclosed, the Company received a civil investigative demand from the U.S. Attorney’s Office for the Southern District of New York that requested information relating to the Company’s contracts with, services from and payments to pharmacy benefit managers with respect to Maxalt and Levitra from January 1, 2006 to the present. The Company has been informed that the government is no longer pursuing the investigation as to Merck. As previously disclosed, the Company received a subpoena from the Office of Inspector General of the U.S. Department of Health and Human Services on behalf of the U.S. Attorney’s Office for the District of Maryland and the Civil Division of the U.S. Department of Justice that requested information relating to the Company’s marketing of Singulair and Dulera Inhalation Aerosol and certain of its other marketing activities from January 1, 2006 to 2016. The Company has been informed by the Justice Department that the investigation is closed. 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 Merck KGaA Litigation 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 and Singapore alleging, among other things, unfair competition, trademark infringement and corporate name infringement. In the UK, Australia and Singapore, 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. 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 no further appeal was pursued. 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. On March 20, 2018, the UK High Court listed the UK re-hearing for the week commencing July 2, 2018. Patent Litigation From time to time, generic manufacturers of pharmaceutical products file abbreviated New Drug Applications with the U.S. Food and Drug Administration (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 France, Italy, Ireland, Spain, Portugal and Norway. The Company has filed for preliminary injunctions in many countries that are still pending decision. A preliminary injunction has been granted in Germany. Preliminary injunctions have been denied in France, Spain and Ireland and the Company is appealing those decisions. The Company will 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., 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 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. Gilead Patent Litigation and Opposition In August 2013, Gilead Sciences, Inc. (Gilead) filed a lawsuit in the U.S. District Court for the Northern District of California seeking a declaration that two Company patents were invalid and not infringed by the sale of their two sofosbuvir containing products, Sovaldi and Harvoni. The Company filed a counterclaim that the sale of these products did infringe these two patents and sought a reasonable royalty for the past, present and future sales of these products. In March 2016, at the conclusion of a jury trial, the patents were found to be not invalid and infringed. The jury awarded the Company $200 million as a royalty for sales of these products up to December 2015. After the conclusion of the jury trial, the court held a bench trial on the equitable defenses raised by Gilead. In June 2016, the court found for Gilead and determined that Merck could not collect the jury award and that the patents were unenforceable with respect to Gilead. The Company appealed the court’s decision. Gilead also asked the court to overturn the jury’s decision on validity. The court held a hearing on Gilead’s motion in August 2016, and the court subsequently rejected Gilead’s request, which Gilead appealed. On April 25, 2018, the appeals court affirmed the decisions that both patents were unenforceable against Gilead. The Company, through its Idenix Pharmaceuticals, Inc. subsidiary, has pending litigation against Gilead in the United States, Canada, Germany, France, and Australia based on different patent estates that would also be infringed by Gilead’s sales of these two products. 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. In Australia, the Company was initially unsuccessful and the Full Federal Court affirmed the lower court decision. The Company sought leave to appeal to the High Court of Australia for further review. Leave was denied on April 17, 2018. In Canada, the Company was initially unsuccessful and the Federal Court of Appeals affirmed the lower court decision. The Company sought leave to the Supreme Court of Canada for further review. Leave was denied on April 26, 2018. 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 March 31, 2018 and December 31, 2017 of approximately $155 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. The Company has reached a settlement with the Public Prosecutor, without any admission of liability, resolving these allegations against two Merck subsidiaries for an aggregate of €400 thousand .

Equity

Equity	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Equity	Equity Common Stock Other Paid-In Capital Retained Earnings Accumulated Other Comprehensive Loss Treasury Stock Non- Controlling Interests Total ($ and shares in millions) Shares Par Value Shares Cost Balance at January 1, 2017 3,577 $ 1,788 $ 39,939 $ 44,133 $ (5,226 ) 828 $ (40,546 ) $ 220 $ 40,308 Net income attributable to Merck & Co., Inc. — — — 1,551 — — — — 1,551 Other comprehensive income, net of taxes — — — — 146 — — — 146 Cash dividends declared on common stock — — — (1,297 ) — — — — (1,297 ) Treasury stock shares purchased — — — — — 16 (1,019 ) — (1,019 ) Share-based compensation plans and other — — (40 ) — — (7 ) 408 — 368 Acquisition of Vallée — — — — — — — 25 25 Net income attributable to noncontrolling interests — — — — — — — 5 5 Other changes in noncontrolling ownership interests — — — — — — — 1 1 Balance at March 31, 2017 3,577 $ 1,788 $ 39,899 $ 44,387 $ (5,080 ) 837 $ (41,157 ) $ 251 $ 40,088 Balance at January 1, 2018 3,577 $ 1,788 $ 39,902 $ 41,350 $ (4,910 ) 880 $ (43,794 ) $ 233 $ 34,569 Adoption of new accounting standards (see Note 1) — — — 322 (274 ) — — — 48 Net income attributable to Merck & Co., Inc. — — — 736 — — — — 736 Other comprehensive income, net of taxes — — — — 124 — — — 124 Cash dividends declared on common stock — — — (1,301 ) — — — — (1,301 ) Treasury stock shares purchased — — — — — 10 (566 ) — (566 ) Share-based compensation plans and other — — (28 ) — — (5 ) 319 — 291 Net income attributable to noncontrolling interests — — — — — — — 5 5 Distributions attributable to noncontrolling interests — — — — — — — (5 ) (5 ) Balance at March 31, 2018 3,577 $ 1,788 $ 39,874 $ 41,107 $ (5,060 ) 885 $ (44,041 ) $ 233 $ 33,901

Share-Based Compensation Plans

Share-Based Compensation Plans	3 Months Ended
	Mar. 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. The following table provides the amounts of share-based compensation cost recorded in the Condensed Consolidated Statement of Income: Three Months Ended ($ in millions) 2018 2017 Pretax share-based compensation expense $ 80 $ 74 Income tax benefit (15 ) (22 ) Total share-based compensation expense, net of taxes $ 65 $ 52 During the first three months of 2018 and 2017 , the Company granted 121 thousand RSUs with a weighted-average grant date fair value of $55.88 per RSU and 86 thousand RSUs with a weighted-average grant date fair value of $64.20 per RSU, respectively. During the first three months of 2018 and 2017 , the Company granted 46 thousand stock options with a weighted-average exercise price of $55.88 per option and 190 thousand stock options with a weighted-average exercise price of $64.20 per option, respectively. The weighted-average fair value of options granted for the first three months of 2018 and 2017 was $7.83 and $7.89 per option, respectively, and was determined using the following assumptions: Three Months Ended 2018 2017 Expected dividend yield 3.4 % 3.7 % Risk-free interest rate 2.7 % 2.0 % Expected volatility 19.5 % 19.7 % Expected life (years) 6.0 6.2 At March 31, 2018 , there was $798 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 2.4 years . The Company typically communicates the value of annual share-based compensation awards to employees during the first quarter, but the related share amounts are not established and communicated until early May. Therefore, while the number of RSU and stock option grants disclosed above do not reflect any amounts relating to the annual grants, share-based compensation costs for the first quarter of 2018 and 2017 and unrecognized compensation expense at March 31, 2018 reflect an impact relating to the awards communicated to employees. For segment reporting, share-based compensation costs are unallocated expenses.

Pension and Other Postretiremen

Pension and Other Postretirement Benefit Plans	3 Months Ended
	Mar. 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. The net periodic benefit cost (credit) of such plans consisted of the following components: Three Months Ended 2018 2017 ($ in millions) U.S. International U.S. International Service cost $ 83 $ 67 $ 77 $ 61 Interest cost 108 46 113 41 Expected return on plan assets (214 ) (113 ) (218 ) (94 ) Amortization of unrecognized prior service credit (13 ) (3 ) (13 ) (2 ) Net loss amortization 56 21 44 23 Termination benefits 11 — 5 1 Curtailments (2 ) — 3 — Settlements 1 — — — $ 30 $ 18 $ 11 $ 30 The Company provides medical benefits, principally to its eligible U.S. retirees and similar benefits to their dependents, through its other postretirement benefit plans. The net cost (credit) of such plans consisted of the following components: Three Months Ended ($ in millions) 2018 2017 Service cost $ 14 $ 14 Interest cost 18 20 Expected return on plan assets (21 ) (19 ) Amortization of unrecognized prior service credit (21 ) (25 ) Termination benefits 1 1 Curtailments (4 ) (3 ) $ (13 ) $ (12 ) In connection with restructuring actions (see Note 5), termination charges were recorded on pension and other postretirement benefit plans related to expanded eligibility for certain employees exiting Merck. Also, in connection with these restructuring actions, curtailments were recorded on pension and other postretirement benefit plans as reflected in the tables above. The components of net periodic benefit cost (credit) other than the service cost component are included in Other (income) expense, net (see Note 12), with the exception of certain amounts for termination benefits and curtailments, which are recorded in Restructuring costs if the event giving rise to the termination benefits or curtailment is related to restructuring actions as noted above.

Other (Income) Expense, Net

Other (Income) Expense, Net	3 Months Ended
	Mar. 31, 2018
Other Income and Expenses [Abstract]
Other (Income) Expense, Net	Other (Income) Expense, Net Other (income) expense, net, consisted of: Three Months Ended ($ in millions) 2018 2017 Interest income $ (85 ) $ (97 ) Interest expense 185 182 Exchange losses (gains) 7 (8 ) Equity losses from affiliates 52 13 Net periodic defined benefit plan (credit) cost other than service cost (135 ) (129 ) Other, net (315 ) (32 ) $ (291 ) $ (71 ) Other, net (as reflected in the table above) includes a $115 million gain on the settlement of certain patent litigation (see Note 8). Interest paid for the three months ended March 31, 2018 and 2017 was $186 million and $162 million , respectively.

Taxes on Income

Taxes on Income	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Taxes on Income	Taxes on Income The effective income tax rates of 44.9% and 22.3% for the first quarter of 2018 and 2017 , respectively, reflect the impacts of acquisition and divestiture-related costs and restructuring costs, partially offset by the beneficial impact of foreign earnings. In addition, the effective income tax rate for the first quarter of 2018 reflects the unfavorable impact of a $1.4 billion aggregate pretax charge recorded in connection with the formation of an oncology collaboration with Eisai for which no tax benefit was recognized. On December 22, 2017, new U.S. tax legislation known as the Tax Cuts and Jobs Act of 2017 (TCJA) was enacted. 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 as described below. However, application of certain provisions of the TCJA was and remains subject to further interpretation and in these instances the Company made a reasonable estimate of the effects of the TCJA. No changes to these amounts were recognized in the first quarter of 2018 and they remain provisional. 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 for its one-time transition tax liability of $5.3 billion . Merck has not yet finalized its calculation of the total post-1986 undistributed E&P for these foreign subsidiaries. The transition tax is based in part on the amount of undistributed E&P held in cash and other specified assets; therefore, this amount may change when the Company finalizes its calculation of post-1986 undistributed foreign E&P and finalizes the amounts held in cash or other specified assets. 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. The Company anticipates that it will be able to utilize certain foreign tax credits to partially reduce the transition tax payment, resulting in a net transition tax payment of $5.1 billion . 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 . The deferred tax benefit calculation remains subject to certain clarifications, particularly related to executive compensation and benefits. Beginning in 2018, the TCJA includes a tax on “global intangible low-taxed income” (GILTI) as defined in the TCJA. The Company is allowed to make an accounting policy election to account for the tax effects of the GILTI tax either in the income tax provision in future periods as the tax arises, or as a component of deferred taxes on the related investments in foreign subsidiaries. The Company is currently evaluating the GILTI provisions of the TCJA and the implications on its tax provision and has not finalized the accounting policy election; therefore, the Company has not recorded deferred taxes for GILTI as of December 31, 2017.

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share The calculations of earnings per share are as follows: Three Months Ended ($ and shares in millions except per share amounts) 2018 2017 Net income attributable to Merck & Co., Inc. $ 736 $ 1,551 Average common shares outstanding 2,695 2,745 Common shares issuable (1) 15 21 Average common shares outstanding assuming dilution 2,710 2,766 Basic earnings per common share attributable to Merck & Co., Inc. common shareholders $ 0.27 $ 0.56 Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders $ 0.27 $ 0.56 (1) Issuable primarily under share-based compensation plans. For the three months ended March 31, 2018 and 2017 , 14 million and 2 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)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Changes in AOCI by component are as follows: Three Months Ended March 31, ($ in millions) Derivatives Investments Employee Benefit Plans Cumulative Translation Adjustment Accumulated Other Comprehensive Income (Loss) Balance January 1, 2017, net of taxes $ 338 $ (3 ) $ (3,206 ) $ (2,355 ) $ (5,226 ) Other comprehensive income (loss) before reclassification adjustments, pretax (263 ) 87 (4 ) 263 83 Tax 92 (7 ) 9 46 140 Other comprehensive income (loss) before reclassification adjustments, net of taxes (171 ) 80 5 309 223 Reclassification adjustments, pretax (95 ) (1) (57 ) (2) 28 (3) — (124 ) Tax 34 20 (7 ) — 47 Reclassification adjustments, net of taxes (61 ) (37 ) 21 — (77 ) Other comprehensive income (loss), net of taxes (232 ) 43 26 309 146 Balance March 31, 2017, net of taxes $ 106 $ 40 $ (3,180 ) $ (2,046 ) $ (5,080 ) Balance January 1, 2018, net of taxes $ (108 ) $ (61 ) $ (2,787 ) $ (1,954 ) $ (4,910 ) Other comprehensive income (loss) before reclassification adjustments, pretax (181 ) (112 ) (1 ) 319 25 Tax 38 — 3 (62 ) (21 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes (143 ) (112 ) 2 257 4 Reclassification adjustments, pretax 92 (1) 12 (2) 41 (3) — 145 Tax (19 ) 1 (7 ) — (25 ) Reclassification adjustments, net of taxes 73 13 34 — 120 Other comprehensive income (loss), net of taxes (70 ) (99 ) 36 257 124 Reclassification of provisional stranded tax effects (see Note 1) (23 ) 1 (344 ) 100 (266 ) Adoption of ASU 2016-01 (see Note 1) — (8 ) — — (8 ) Balance March 31, 2018, net of taxes $ (201 ) $ (167 ) $ (3,095 ) $ (1,597 ) $ (5,060 ) (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, these amounts included both debt and equity investments; however, upon adoption of ASU 2016-01 in 2018 (see Note 1), these amounts relate only to available-for-sale debt investments. (3) Includes net amortization of prior service cost and actuarial gains and losses included in net periodic benefit cost (see Note 11).

Segment Reporting

Segment Reporting	3 Months Ended
	Mar. 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 the first quarter of 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. 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. The Company’s Animal Health segment discovers, develops, manufactures and markets animal health products, including vaccines, which the Company sells to veterinarians, distributors and animal producers. The Company’s 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. Sales of the Company’s products were as follows: Three Months Ended March 31, 2018 2017 ($ in millions) U.S. Int’l Total U.S. Int’l Total Pharmaceutical: Oncology Keytruda $ 838 $ 626 $ 1,464 $ 361 $ 223 $ 584 Emend 79 46 125 86 47 133 Temodar 1 56 57 1 65 66 Alliance revenue - Lynparza 24 9 33 — — — Vaccines Gardasil/Gardasil 9 380 280 660 398 134 532 ProQuad/M-M-R II /Varivax 312 80 392 298 57 355 RotaTeq 151 42 193 178 45 224 Pneumovax 23 112 66 179 114 49 163 Zostavax 16 48 65 109 45 154 Hospital Acute Care Bridion 80 124 204 45 102 148 Noxafil 81 94 176 65 76 141 Invanz 91 60 151 82 54 136 Cubicin 47 51 98 54 41 96 Cancidas 3 88 91 5 116 121 Primaxin 5 67 72 — 62 62 Immunology Simponi — 231 231 — 184 184 Remicade — 167 167 — 229 229 Neuroscience Belsomra 23 31 54 20 21 42 Virology Isentress/Isentress HD 128 152 281 143 162 305 Zepatier — 131 131 200 178 378 Cardiovascular Zetia 17 287 305 111 222 334 Vytorin 8 158 167 90 151 241 Atozet — 73 73 — 49 49 Adempas — 68 68 — 84 84 Diabetes Januvia 465 416 880 507 332 839 Janumet 192 352 544 195 302 496 Women’s Health NuvaRing 171 46 216 113 47 160 Implanon/Nexplanon 128 46 174 132 39 170 Diversified Brands Singulair 6 170 175 6 180 186 Nasonex 1 121 122 18 121 139 Cozaar/Hyzaar 7 113 120 3 109 112 Arcoxia — 83 83 — 103 103 Follistim AQ 29 39 67 42 40 81 Dulera 50 7 57 75 7 82 Fosamax (2 ) 57 55 1 60 61 Other pharmaceutical (1) 273 717 989 309 688 995 Total Pharmaceutical segment sales 3,716 5,202 8,919 3,761 4,424 8,185 Animal Health: Livestock 124 529 652 119 459 578 Companion Animals 183 229 413 164 197 361 Total Animal Health segment sales 307 758 1,065 283 656 939 Other segment sales (2) 84 — 84 94 — 94 Total segment sales 4,107 5,960 10,068 4,138 5,080 9,218 Other (3) 26 (56 ) (31 ) 57 159 216 $ 4,133 $ 5,904 $ 10,037 $ 4,195 $ 5,239 $ 9,434 (1) Other pharmaceutical primarily reflects sales of other human health pharmaceutical products, including products within the franchises not listed separately. (2) Represents the non-reportable segments of Healthcare Services and Alliances. (3) Other is primarily comprised of miscellaneous corporate revenues, including revenue hedging activities, as well as third-party manufacturing sales. Other in the first quarter of 2018 and 2017 also includes $21 million and $50 million , respectively, related to the sale of the marketing rights to certain products. Consolidated revenues by geographic area where derived are as follows: Three Months Ended ($ in millions) 2018 2017 United States $ 4,133 $ 4,195 Europe, Middle East and Africa 3,191 2,629 Asia Pacific 1,238 1,001 Japan 737 705 Latin America 532 485 Other 206 419 $ 10,037 $ 9,434 A reconciliation of segment profits to Income before taxes is as follows: Three Months Ended ($ in millions) 2018 2017 Segment profits: Pharmaceutical segment $ 5,804 $ 5,160 Animal Health segment 413 417 Other segments 63 33 Total segment profits 6,280 5,610 Other profits (87 ) 142 Unallocated: Interest income 85 97 Interest expense (185 ) (182 ) Equity income from affiliates (50 ) (12 ) Depreciation and amortization (350 ) (370 ) Research and development (2,982 ) (1,632 ) Amortization of purchase accounting adjustments (733 ) (778 ) Restructuring costs (95 ) (151 ) Other unallocated, net (538 ) (721 ) $ 1,345 $ 2,003 Pharmaceutical segment profits are comprised of segment sales less standard costs, as well as marketing and administrative expenses and research and development costs directly incurred by the segment. Animal Health segment profits are comprised of segment sales, less all materials and production costs, as well as marketing 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 materials and production costs 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 intangible asset impairment charges, gains or losses on sales of businesses, expense or income related to changes in the estimated fair value of contingent consideration, and other miscellaneous income or expense items. In the first quarter of 2018, the Company adopted a new accounting standard related to the classification of certain defined benefit plan costs (see Note 1), 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.

Basis of Presentation (Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of Merck & Co., Inc. (Merck or the Company) have been prepared pursuant to the rules and regulations for reporting on Form 10-Q. Accordingly, certain information and disclosures required by accounting principles generally accepted in the United States for complete consolidated financial statements are not included herein. These interim statements should be read in conjunction with the audited financial statements and notes thereto included in Merck’s Form 10-K filed on February 27, 2018. The results of operations of any interim period are not necessarily indicative of the results of operations for the full year. In the Company’s opinion, all adjustments necessary for a fair statement of these interim statements have been included and are of a normal and recurring nature. Certain reclassifications have been made to prior year amounts to conform to the current presentation.
Recently Adopted and Issued 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 will be applied 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 . See Note 2 for additional information related to the adoption of this standard. 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, less impairment, adjusted for subsequent observable price changes, 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 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 (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 these amounts 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 provisional amount of $266 million with a corresponding increase to Retained earnings (see Note 15). The Company’s policy for releasing the disproportionate income tax effects from Accumulated other comprehensive loss is to utilize the item-by-item approach. The impact of adopting the above standards is as follows: ($ 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 - Debit (Credit) Accounts receivable $ 5 $ 5 Liabilities - Credit (Debit) Income Taxes Payable (3 ) (3 ) Debt 14 14 Deferred Income Taxes (54 ) (54 ) Equity - Credit (Debit) Retained earnings 5 8 54 (11 ) 266 322 Accumulated other comprehensive loss (8 ) (266 ) (274 ) In March 2017, the FASB amended the guidance 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 to adopt the requirement for separate presentation in the income statement of service costs and other components and a prospective transition method to adopt 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 was reclassified to Other (income) expense, net from the previous classification within Materials and production costs, Marketing and administrative expenses and Research and development costs (see Note 12). 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 prior year period 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. Recently Issued Accounting Standards Not Yet Adopted In February 2016, the FASB issued new accounting guidance for the accounting and reporting of leases. 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 guidance will be effective for interim and annual periods beginning in 2019 and will be adopted using a modified retrospective approach. The Company intends to elect available practical expedients. The Company is currently evaluating the impact of adoption on its consolidated financial statements. 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 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 new guidance is effective for interim and annual periods in 2020. Early adoption is permitted. The Company does not anticipate that the adoption of the new guidance will have a material effect on its consolidated financial statements.
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 Note 1). 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 provides principles that an entity applies to report useful information about the amount, timing, and uncertainty of revenue and cash flows arising from its contracts to provide goods or services to customers. The core principle 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. The Company’s significant accounting policies are detailed in Note 2 to the consolidated financial statements included in Merck’s Annual Report on Form 10-K for the year ended December 31, 2017. Changes to the Company’s revenue recognition policy as a result of adopting ASC 606 are described below. See Note 16 for disaggregated revenue disclosures. Revenue Recognition — 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. 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. Merck’s payment terms for U.S. customers are typically net 36 days from receipt of invoice; however, certain products 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 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 also used for certain types of variable consideration. 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 provision for aggregate customer discounts covers chargebacks and rebates. Chargebacks are discounts that occur when a contracted customer purchases directly 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. These discounts, in the aggregate, reduced U.S. sales by $2.4 billion and $2.5 billion in the first quarter of 2018 and 2017 , respectively. 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. In all cases, the Company applies an estimated factor against its actual invoiced sales to represent the expected level of future discount or rebate obligation 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 on a limited basis in certain countries.
Legal defense costs	Legal defense costs expected to be incurred in connection with a loss contingency are accrued when probable and reasonably estimable.

Basis of Presentation (Tables)

Basis of Presentation (Tables)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Impact of Adopting Standard	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 - Debit (Credit) Accounts receivable $ 5 $ 5 Liabilities - Credit (Debit) Income Taxes Payable (3 ) (3 ) Debt 14 14 Deferred Income Taxes (54 ) (54 ) Equity - Credit (Debit) Retained earnings 5 8 54 (11 ) 266 322 Accumulated other comprehensive loss (8 ) (266 ) (274 ) The following table provides the effects of adopting ASC 606 on the Consolidated Statement of Income in the first quarter of 2018: Three Months Ended March 31, 2018 ($ in millions) As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Sales $ 10,037 $ (24 ) $ 10,013 Materials and production 3,184 (11 ) 3,173 Income before taxes 1,345 (13 ) 1,332 Taxes on income 604 (2 ) 602 Net income attributable to Merck & Co., Inc. 736 (11 ) 725 The following table provides the effects of adopting ASC 606 on the consolidated balance sheet as of March 31, 2018: March 31, 2018 ($ in millions) As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Assets Accounts receivable $ 7,245 $ (36 ) $ 7,209 Inventories 5,382 13 5,395 Liabilities Accrued and other current liabilities 9,709 (3 ) 9,706 Income taxes payable 717 (4 ) 713 Equity Retained earnings 41,107 (16 ) 41,091

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Effects of Adopting ASC 606	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 - Debit (Credit) Accounts receivable $ 5 $ 5 Liabilities - Credit (Debit) Income Taxes Payable (3 ) (3 ) Debt 14 14 Deferred Income Taxes (54 ) (54 ) Equity - Credit (Debit) Retained earnings 5 8 54 (11 ) 266 322 Accumulated other comprehensive loss (8 ) (266 ) (274 ) The following table provides the effects of adopting ASC 606 on the Consolidated Statement of Income in the first quarter of 2018: Three Months Ended March 31, 2018 ($ in millions) As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Sales $ 10,037 $ (24 ) $ 10,013 Materials and production 3,184 (11 ) 3,173 Income before taxes 1,345 (13 ) 1,332 Taxes on income 604 (2 ) 602 Net income attributable to Merck & Co., Inc. 736 (11 ) 725 The following table provides the effects of adopting ASC 606 on the consolidated balance sheet as of March 31, 2018: March 31, 2018 ($ in millions) As Reported Effects of Adopting ASC 606 Amounts Without Adoption of ASC 606 Assets Accounts receivable $ 7,245 $ (36 ) $ 7,209 Inventories 5,382 13 5,395 Liabilities Accrued and other current liabilities 9,709 (3 ) 9,706 Income taxes payable 717 (4 ) 713 Equity Retained earnings 41,107 (16 ) 41,091

Collaborative Arrangements (Tab

Collaborative Arrangements (Tables)	3 Months Ended
	Mar. 31, 2018
Collaborative Arrangements [Abstract]
Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions	Summarized information related to this collaboration is as follows: Three Months Ended ($ in millions) 2018 Alliance revenues (net of commercialization costs) $ 33 Materials and production (1) 12 Marketing and administrative 7 Research and development 29 Receivables from AstraZeneca 31 Payables to AstraZeneca 783 (1) Includes amortization of intangible assets. Summarized information related to this collaboration is as follows: Three Months Ended ($ in millions) 2018 2017 Net product sales recorded by Merck $ 43 $ 31 Merck’s profit share from sales in Bayer's marketing territories 25 53 Total sales 68 84 Materials and production (1) 27 23 Marketing and administrative 8 7 Research and development 32 22 Receivables from Bayer 35 Payables to Bayer — (1) Includes amortization of intangible assets.

Restructuring (Tables)

Restructuring (Tables)	3 Months Ended
	Mar. 31, 2018
Restructuring and Related Activities [Abstract]
Charges Related to Restructuring Program Activities by Type of Cost	The following tables summarize the charges related to restructuring program activities by type of cost: Three Months Ended March 31, 2018 ($ in millions) Separation Costs Accelerated Depreciation Other Total Materials and production $ — $ — $ 6 $ 6 Marketing and administrative — 1 — 1 Research and development — (3 ) 5 2 Restructuring costs 55 — 40 95 $ 55 $ (2 ) $ 51 $ 104 Three Months Ended March 31, 2017 ($ in millions) Separation Costs Accelerated Depreciation Other Total Materials and production $ — $ 51 $ 12 $ 63 Marketing and administrative — — 1 1 Research and development — (2 ) 2 — Restructuring costs 84 — 67 151 $ 84 $ 49 $ 82 $ 215
Charges and Spending Relating to Restructuring Activities by Program	The following table summarizes the charges and spending relating to restructuring program activities for the three months ended March 31, 2018 : ($ in millions) Separation Costs Accelerated Depreciation Other Total Restructuring reserves January 1, 2018 $ 619 $ — $ 128 $ 747 Expense 55 (2 ) 51 104 (Payments) receipts, net (139 ) — (64 ) (203 ) Non-cash activity — 2 1 3 Restructuring reserves March 31, 2018 (1) $ 535 $ — $ 116 $ 651 (1) The remaining cash outlays are expected to be substantially completed by the end of 2020.

Financial Instruments (Tables)

Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Effect of Net Investment Hedges on OCI and the Consolidated Statement of Income	The effect of the Company’s net investment hedges on OCI and the Consolidated Statement of Income is shown below: Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income (1) Location of Pretax (Gain) Loss Recognized in Income For Amounts Excluded from Effectiveness Testing Amount of Pretax (Gain) Loss Recognized in Income For Amounts Excluded from Effectiveness Testing Three Months Ended March 31, Three Months Ended March 31, ($ in millions) 2018 2017 2018 2017 Net Investment Hedging Relationships Foreign exchange contracts $ (2 ) $ — Other (income) expense, net $ — $ — Euro-denominated notes 178 135 Other (income) expense, net — — (1) No amounts were reclassified from AOCI into income related to the sale of a subsidiary.
Summary of Interest Rate Swaps Held	At March 31, 2018 , the Company was a party to 26 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. ($ in millions) March 31, 2018 Debt Instrument Par Value of Debt Number of Interest Rate Swaps Held Total Swap Notional Amount 1.30% notes due 2018 $ 1,000 4 $ 1,000 5.00% notes due 2019 1,250 3 550 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
Amounts Recorded on Balance Sheet Related to Fair Value Hedges	The table below presents the location of amounts recorded on the Consolidated Balance Sheet related to cumulative basis adjustments for fair value hedges: Carrying Amount of Hedged Assets (Liabilities) Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount ($ in millions) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Balance Sheet Line Item in which Hedged Item is Included Loans payable and current portion of long-term debt $ (998 ) $ (983 ) $ 2 $ 17 Long-Term Debt (1) (5,083 ) (5,146 ) 106 41 (1) Amounts include hedging adjustment gains related to discontinued hedging relationships of $9 million and $11 million at March 31, 2018 and December 31, 2017, respectively.
Fair Value of Derivatives on a Gross Basis Segregated between those Derivatives that are Designated as Hedging Instruments and those that are Not Designated as Hedging Instruments	Presented in the table below is the fair value of derivatives on a gross basis segregated between those derivatives that are designated as hedging instruments and those that are not designated as hedging instruments: March 31, 2018 December 31, 2017 Fair Value of Derivative U.S. Dollar Notional Fair Value of Derivative U.S. Dollar Notional ($ in millions) 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 — 1 1,000 — 3 1,000 Interest rate swap contracts Other noncurrent liabilities — 114 5,200 — 52 4,650 Foreign exchange contracts Other current assets 21 — 3,584 51 — 4,216 Foreign exchange contracts Other assets 30 — 2,407 38 — 1,936 Foreign exchange contracts Accrued and other current liabilities — 119 3,205 — 71 2,014 Foreign exchange contracts Other noncurrent liabilities — 1 56 — 1 20 $ 51 $ 235 $ 15,452 $ 91 $ 127 $ 14,386 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts Other current assets $ 58 $ — $ 5,434 $ 39 $ — $ 3,778 Foreign exchange contracts Accrued and other current liabilities — 89 6,764 — 90 7,431 $ 58 $ 89 $ 12,198 $ 39 $ 90 $ 11,209 $ 109 $ 324 $ 27,650 $ 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: March 31, 2018 December 31, 2017 ($ in millions) Asset Liability Asset Liability Gross amounts recognized in the consolidated balance sheet $ 109 $ 324 $ 130 $ 217 Gross amount subject to offset in master netting arrangements not offset in the consolidated balance sheet (103 ) (103 ) (94 ) (94 ) Cash collateral received — — (3 ) — Net amounts $ 6 $ 221 $ 33 $ 123
Location and Amount of Pretax (Gains) Losses of 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: Three Months Ended Three Months Ended ($ in millions) Sales Other (income) expense, net (1) Other comprehensive income (loss) Sales Other (income) expense, net (1) Other comprehensive income (loss) Financial Statement Line Items in which Effects of Fair Value or Cash Flow Hedges are Recorded $ 10,037 $ (291 ) $ 124 $ 9,434 $ (71 ) $ 146 (Gain) loss on fair value hedging relationships Interest rate swap contracts Hedged items — (62 ) — — (16 ) — Derivatives designated as hedging instruments — 62 — — 4 — Impact of cash flow hedging relationships Foreign exchange contracts Amount of (loss) recognized in OCI on derivatives — — (181 ) — — (263 ) (Decrease) increase in Sales as a result of AOCI reclassifications (93 ) — 93 94 — (94 ) (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 statements effects of derivatives not designated as hedging instruments: Amount of Derivative Pretax (Gain) Loss Recognized in Income Location of Derivative Pretax (Gain) Loss Recognized in Income Three Months Ended March 31, ($ in millions) 2018 2017 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts (1) Other (income) expense, net $ 28 $ (47 ) Foreign exchange contracts (2) Sales 8 — (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 Available-for-sale Investments	Information on investments in debt and equity securities is as follows: March 31, 2018 December 31, 2017 Fair Value Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized ($ in millions) Gains Losses Gains Losses Corporate notes and bonds $ 9,860 $ 9,978 $ 3 $ (121 ) $ 9,806 $ 9,837 $ 9 $ (40 ) U.S. government and agency securities 1,810 1,833 — (23 ) 2,042 2,059 — (17 ) Asset-backed securities 1,569 1,585 1 (17 ) 1,542 1,548 1 (7 ) Foreign government bonds 759 769 — (10 ) 733 739 — (6 ) Commercial paper 130 130 — — 159 159 — — Mortgage-backed securities 78 79 — (1 ) 626 634 1 (9 ) Total debt securities $ 14,206 $ 14,374 $ 4 $ (172 ) $ 14,908 $ 14,976 $ 11 $ (79 ) Publicly traded equity securities (1) 332 275 265 16 (6 ) Total debt and publicly traded equity securities $ 14,538 $ 15,183 $ 15,241 $ 27 $ (85 ) (1) Pursuant to the adoption of ASU 2016-01 (see Note 1), beginning on January 1, 2018, changes in the fair value of publicly traded equity securities are recognized in net income. Unrealized net gains of $44 million were recognized during the first quarter of 2018 on equity securities still held at March 31, 2018.
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	Financial assets and liabilities measured at fair value on a recurring basis are summarized below: Fair Value Measurements Using Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total ($ in millions) March 31, 2018 December 31, 2017 Assets Investments Corporate notes and bonds $ — $ 9,741 $ — $ 9,741 $ — $ 9,678 $ — $ 9,678 U.S. government and agency securities — 1,585 — 1,585 68 1,767 — 1,835 Asset-backed securities (1) — 1,517 — 1,517 — 1,476 — 1,476 Foreign government bonds — 759 — 759 — 732 — 732 Commercial paper — 130 — 130 — 159 — 159 Mortgage-backed securities — — — — — 547 — 547 Publicly traded equity securities 164 — — 164 104 — — 104 164 13,732 — 13,896 172 14,359 — 14,531 Other assets (2) U.S. government and agency securities 64 161 — 225 — 207 — 207 Corporate notes and bonds — 119 — 119 — 128 — 128 Mortgage-backed securities — 78 — 78 — 79 — 79 Asset-backed securities (1) — 52 — 52 — 66 — 66 Foreign government bonds — — — — — 1 — 1 Publicly traded equity securities 168 — — 168 171 — — 171 232 410 — 642 171 481 — 652 Derivative assets (3) Purchased currency options — 46 — 46 — 80 — 80 Forward exchange contracts — 63 — 63 — 48 — 48 Interest rate swaps — — — — — 2 — 2 — 109 — 109 — 130 — 130 Total assets $ 396 $ 14,251 $ — $ 14,647 $ 343 $ 14,970 $ — $ 15,313 Liabilities Other liabilities Contingent consideration $ — $ — $ 919 $ 919 $ — $ — $ 935 $ 935 Derivative liabilities (3) Forward exchange contracts — 208 — 208 — 162 — 162 Interest rate swaps — 115 — 115 — 55 — 55 Written currency options — 1 — 1 — — — — — 324 — 324 — 217 — 217 Total liabilities $ — $ 324 $ 919 $ 1,243 $ — $ 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.
Information About the Changes in Liabilities for Contingent Consideration	Summarized information about the changes in liabilities for contingent consideration is as follows: Three Months Ended March 31, ($ in millions) 2018 2017 Fair value January 1 $ 935 $ 891 Changes in fair value (1) 36 34 Additions 8 — Payments (60 ) — Fair value March 31 (2) $ 919 $ 925 (1) Recorded in Research and development expenses, Materials and production costs and Other (income) expense, net . Includes cumulative translation adjustments. (2) Includes $337 million recorded as a current liability for amounts expected to be paid within the next 12 months.

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories consisted of: ($ in millions) March 31, 2018 December 31, 2017 Finished goods $ 1,530 $ 1,334 Raw materials and work in process 4,764 4,703 Supplies 199 201 Total (approximates current cost) 6,493 6,238 Increase to LIFO costs 25 45 $ 6,518 $ 6,283 Recognized as: Inventories $ 5,382 $ 5,096 Other assets 1,136 1,187

Equity (Tables)

Equity (Tables)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Equity	Common Stock Other Paid-In Capital Retained Earnings Accumulated Other Comprehensive Loss Treasury Stock Non- Controlling Interests Total ($ and shares in millions) Shares Par Value Shares Cost Balance at January 1, 2017 3,577 $ 1,788 $ 39,939 $ 44,133 $ (5,226 ) 828 $ (40,546 ) $ 220 $ 40,308 Net income attributable to Merck & Co., Inc. — — — 1,551 — — — — 1,551 Other comprehensive income, net of taxes — — — — 146 — — — 146 Cash dividends declared on common stock — — — (1,297 ) — — — — (1,297 ) Treasury stock shares purchased — — — — — 16 (1,019 ) — (1,019 ) Share-based compensation plans and other — — (40 ) — — (7 ) 408 — 368 Acquisition of Vallée — — — — — — — 25 25 Net income attributable to noncontrolling interests — — — — — — — 5 5 Other changes in noncontrolling ownership interests — — — — — — — 1 1 Balance at March 31, 2017 3,577 $ 1,788 $ 39,899 $ 44,387 $ (5,080 ) 837 $ (41,157 ) $ 251 $ 40,088 Balance at January 1, 2018 3,577 $ 1,788 $ 39,902 $ 41,350 $ (4,910 ) 880 $ (43,794 ) $ 233 $ 34,569 Adoption of new accounting standards (see Note 1) — — — 322 (274 ) — — — 48 Net income attributable to Merck & Co., Inc. — — — 736 — — — — 736 Other comprehensive income, net of taxes — — — — 124 — — — 124 Cash dividends declared on common stock — — — (1,301 ) — — — — (1,301 ) Treasury stock shares purchased — — — — — 10 (566 ) — (566 ) Share-based compensation plans and other — — (28 ) — — (5 ) 319 — 291 Net income attributable to noncontrolling interests — — — — — — — 5 5 Distributions attributable to noncontrolling interests — — — — — — — (5 ) (5 ) Balance at March 31, 2018 3,577 $ 1,788 $ 39,874 $ 41,107 $ (5,060 ) 885 $ (44,041 ) $ 233 $ 33,901

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Amounts of Share-Based Compensation Cost Recorded in Consolidated Statement of Income	The following table provides the amounts of share-based compensation cost recorded in the Condensed Consolidated Statement of Income: Three Months Ended ($ in millions) 2018 2017 Pretax share-based compensation expense $ 80 $ 74 Income tax benefit (15 ) (22 ) Total share-based compensation expense, net of taxes $ 65 $ 52
Assumptions Used to Determine Weighted-Average Fair Value of Options Granted	The weighted-average fair value of options granted for the first three months of 2018 and 2017 was $7.83 and $7.89 per option, respectively, and was determined using the following assumptions: Three Months Ended 2018 2017 Expected dividend yield 3.4 % 3.7 % Risk-free interest rate 2.7 % 2.0 % Expected volatility 19.5 % 19.7 % Expected life (years) 6.0 6.2

Pension and Other Postretirem33

Pension and Other Postretirement Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2018
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Components of net cost of defined benefit plans	The Company has defined benefit pension plans covering eligible employees in the United States and in certain of its international subsidiaries. The net periodic benefit cost (credit) of such plans consisted of the following components: Three Months Ended 2018 2017 ($ in millions) U.S. International U.S. International Service cost $ 83 $ 67 $ 77 $ 61 Interest cost 108 46 113 41 Expected return on plan assets (214 ) (113 ) (218 ) (94 ) Amortization of unrecognized prior service credit (13 ) (3 ) (13 ) (2 ) Net loss amortization 56 21 44 23 Termination benefits 11 — 5 1 Curtailments (2 ) — 3 — Settlements 1 — — — $ 30 $ 18 $ 11 $ 30
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Components of net cost of defined benefit plans	The Company provides medical benefits, principally to its eligible U.S. retirees and similar benefits to their dependents, through its other postretirement benefit plans. The net cost (credit) of such plans consisted of the following components: Three Months Ended ($ in millions) 2018 2017 Service cost $ 14 $ 14 Interest cost 18 20 Expected return on plan assets (21 ) (19 ) Amortization of unrecognized prior service credit (21 ) (25 ) Termination benefits 1 1 Curtailments (4 ) (3 ) $ (13 ) $ (12 )

Other (Income) Expense, Net (Ta

Other (Income) Expense, Net (Tables)	3 Months Ended
	Mar. 31, 2018
Other Income and Expenses [Abstract]
Other (Income) Expense, Net	Other (income) expense, net, consisted of: Three Months Ended ($ in millions) 2018 2017 Interest income $ (85 ) $ (97 ) Interest expense 185 182 Exchange losses (gains) 7 (8 ) Equity losses from affiliates 52 13 Net periodic defined benefit plan (credit) cost other than service cost (135 ) (129 ) Other, net (315 ) (32 ) $ (291 ) $ (71 )

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Calculations of Earnings Per Share	The calculations of earnings per share are as follows: Three Months Ended ($ and shares in millions except per share amounts) 2018 2017 Net income attributable to Merck & Co., Inc. $ 736 $ 1,551 Average common shares outstanding 2,695 2,745 Common shares issuable (1) 15 21 Average common shares outstanding assuming dilution 2,710 2,766 Basic earnings per common share attributable to Merck & Co., Inc. common shareholders $ 0.27 $ 0.56 Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders $ 0.27 $ 0.56 (1) Issuable primarily under share-based compensation plans.

Other Comprehensive Income (L36

Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Changes in AOCI by Component	Changes in AOCI by component are as follows: Three Months Ended March 31, ($ in millions) Derivatives Investments Employee Benefit Plans Cumulative Translation Adjustment Accumulated Other Comprehensive Income (Loss) Balance January 1, 2017, net of taxes $ 338 $ (3 ) $ (3,206 ) $ (2,355 ) $ (5,226 ) Other comprehensive income (loss) before reclassification adjustments, pretax (263 ) 87 (4 ) 263 83 Tax 92 (7 ) 9 46 140 Other comprehensive income (loss) before reclassification adjustments, net of taxes (171 ) 80 5 309 223 Reclassification adjustments, pretax (95 ) (1) (57 ) (2) 28 (3) — (124 ) Tax 34 20 (7 ) — 47 Reclassification adjustments, net of taxes (61 ) (37 ) 21 — (77 ) Other comprehensive income (loss), net of taxes (232 ) 43 26 309 146 Balance March 31, 2017, net of taxes $ 106 $ 40 $ (3,180 ) $ (2,046 ) $ (5,080 ) Balance January 1, 2018, net of taxes $ (108 ) $ (61 ) $ (2,787 ) $ (1,954 ) $ (4,910 ) Other comprehensive income (loss) before reclassification adjustments, pretax (181 ) (112 ) (1 ) 319 25 Tax 38 — 3 (62 ) (21 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes (143 ) (112 ) 2 257 4 Reclassification adjustments, pretax 92 (1) 12 (2) 41 (3) — 145 Tax (19 ) 1 (7 ) — (25 ) Reclassification adjustments, net of taxes 73 13 34 — 120 Other comprehensive income (loss), net of taxes (70 ) (99 ) 36 257 124 Reclassification of provisional stranded tax effects (see Note 1) (23 ) 1 (344 ) 100 (266 ) Adoption of ASU 2016-01 (see Note 1) — (8 ) — — (8 ) Balance March 31, 2018, net of taxes $ (201 ) $ (167 ) $ (3,095 ) $ (1,597 ) $ (5,060 ) (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, these amounts included both debt and equity investments; however, upon adoption of ASU 2016-01 in 2018 (see Note 1), these amounts relate only to available-for-sale debt investments. (3) Includes net amortization of prior service cost and actuarial gains and losses included in net periodic benefit cost (see Note 11).

Segment Reporting (Tables)

Segment Reporting (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Sales of Company's products	Sales of the Company’s products were as follows: Three Months Ended March 31, 2018 2017 ($ in millions) U.S. Int’l Total U.S. Int’l Total Pharmaceutical: Oncology Keytruda $ 838 $ 626 $ 1,464 $ 361 $ 223 $ 584 Emend 79 46 125 86 47 133 Temodar 1 56 57 1 65 66 Alliance revenue - Lynparza 24 9 33 — — — Vaccines Gardasil/Gardasil 9 380 280 660 398 134 532 ProQuad/M-M-R II /Varivax 312 80 392 298 57 355 RotaTeq 151 42 193 178 45 224 Pneumovax 23 112 66 179 114 49 163 Zostavax 16 48 65 109 45 154 Hospital Acute Care Bridion 80 124 204 45 102 148 Noxafil 81 94 176 65 76 141 Invanz 91 60 151 82 54 136 Cubicin 47 51 98 54 41 96 Cancidas 3 88 91 5 116 121 Primaxin 5 67 72 — 62 62 Immunology Simponi — 231 231 — 184 184 Remicade — 167 167 — 229 229 Neuroscience Belsomra 23 31 54 20 21 42 Virology Isentress/Isentress HD 128 152 281 143 162 305 Zepatier — 131 131 200 178 378 Cardiovascular Zetia 17 287 305 111 222 334 Vytorin 8 158 167 90 151 241 Atozet — 73 73 — 49 49 Adempas — 68 68 — 84 84 Diabetes Januvia 465 416 880 507 332 839 Janumet 192 352 544 195 302 496 Women’s Health NuvaRing 171 46 216 113 47 160 Implanon/Nexplanon 128 46 174 132 39 170 Diversified Brands Singulair 6 170 175 6 180 186 Nasonex 1 121 122 18 121 139 Cozaar/Hyzaar 7 113 120 3 109 112 Arcoxia — 83 83 — 103 103 Follistim AQ 29 39 67 42 40 81 Dulera 50 7 57 75 7 82 Fosamax (2 ) 57 55 1 60 61 Other pharmaceutical (1) 273 717 989 309 688 995 Total Pharmaceutical segment sales 3,716 5,202 8,919 3,761 4,424 8,185 Animal Health: Livestock 124 529 652 119 459 578 Companion Animals 183 229 413 164 197 361 Total Animal Health segment sales 307 758 1,065 283 656 939 Other segment sales (2) 84 — 84 94 — 94 Total segment sales 4,107 5,960 10,068 4,138 5,080 9,218 Other (3) 26 (56 ) (31 ) 57 159 216 $ 4,133 $ 5,904 $ 10,037 $ 4,195 $ 5,239 $ 9,434 (1) Other pharmaceutical primarily reflects sales of other human health pharmaceutical products, including products within the franchises not listed separately. (2) Represents the non-reportable segments of Healthcare Services and Alliances. (3) Other is primarily comprised of miscellaneous corporate revenues, including revenue hedging activities, as well as third-party manufacturing sales. Other in the first quarter of 2018 and 2017 also includes $21 million and $50 million , respectively, related to the sale of the marketing rights to certain products.
Consolidated revenues by geographic area	Consolidated revenues by geographic area where derived are as follows: Three Months Ended ($ in millions) 2018 2017 United States $ 4,133 $ 4,195 Europe, Middle East and Africa 3,191 2,629 Asia Pacific 1,238 1,001 Japan 737 705 Latin America 532 485 Other 206 419 $ 10,037 $ 9,434
Reconciliation of segment profits to income before taxes	A reconciliation of segment profits to Income before taxes is as follows: Three Months Ended ($ in millions) 2018 2017 Segment profits: Pharmaceutical segment $ 5,804 $ 5,160 Animal Health segment 413 417 Other segments 63 33 Total segment profits 6,280 5,610 Other profits (87 ) 142 Unallocated: Interest income 85 97 Interest expense (185 ) (182 ) Equity income from affiliates (50 ) (12 ) Depreciation and amortization (350 ) (370 ) Research and development (2,982 ) (1,632 ) Amortization of purchase accounting adjustments (733 ) (778 ) Restructuring costs (95 ) (151 ) Other unallocated, net (538 ) (721 ) $ 1,345 $ 2,003

Basis of Presentation - Adoptio

Basis of Presentation - Adoption of New Accounting Standards - Narrative (Details) $ in Millions	Jan. 01, 2018USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	$ (8)
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	5
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	8
Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	54
Accounting Standards Update 2017-12 | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	$ (11)

Basis of Presentation - Impact

Basis of Presentation - Impact of Adopting Standards (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable	$ 7,245		$ 6,873
Liabilities
Income taxes payable	717		708
Debt	2,055		3,057
Deferred Income Taxes	2,206		2,219
Equity
Retained earnings	41,107		41,350
Accumulated other comprehensive loss	5,060		$ 4,910
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)
ASU 2016-01 (Financial Instruments)
Equity
Retained earnings		8
Accumulated other comprehensive loss		(8)
ASU 2016-16 (Intra-Entity Transfers of Assets Other than Inventory)
Liabilities
Deferred Income Taxes		(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)
Effects of Adopting ASC 606 | ASU 2014-09 (Revenue)
Assets
Accounts receivable	(36)	5
Liabilities
Income taxes payable	(4)
Equity
Retained earnings	$ (16)	$ 5

Summary of Significant Accoun40

Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Billions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Sales discounts for products	$ 2.4	$ 2.5
Return period after expiration date of product	12 months
Minimum
Disaggregation of Revenue [Line Items]
Return period prior to expiration date of product	3 months
Minimum | United States
Disaggregation of Revenue [Line Items]
Payment terms	36 days
Minimum | Outside of the United States
Disaggregation of Revenue [Line Items]
Payment terms	30 days
Maximum
Disaggregation of Revenue [Line Items]
Return period prior to expiration date of product	6 months
Maximum | United States
Disaggregation of Revenue [Line Items]
Payment terms	90 days
Maximum | Outside of the United States
Disaggregation of Revenue [Line Items]
Payment terms	90 days

Summary of Significant Accoun41

Summary of Significant Accounting Policies - Effects of Adopting ASC 606 (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	$ 10,037	$ 9,434
Materials and production	3,184	3,049
Income before taxes	1,345	2,003
Taxes on income	604	447
Net income attributable to Merck & Co., Inc.	736	$ 1,551
Assets
Accounts receivable	7,245			$ 6,873
Inventories	5,382			5,096
Liabilities
Accrued and other current liabilities	9,709			10,427
Income taxes payable	717			708
Equity
Retained earnings	41,107			$ 41,350
Effects of Adopting ASC 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	(24)
Materials and production	(11)
Income before taxes	(13)
Taxes on income	(2)
Net income attributable to Merck & Co., Inc.	(11)
Assets
Accounts receivable	(36)		$ 5
Inventories	13
Liabilities
Accrued and other current liabilities	(3)
Income taxes payable	(4)
Equity
Retained earnings	(16)		$ 5
Amounts Without Adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	10,013
Materials and production	3,173
Income before taxes	1,332
Taxes on income	602
Net income attributable to Merck & Co., Inc.	725
Assets
Accounts receivable	7,209
Inventories	5,395
Liabilities
Accrued and other current liabilities	9,706
Income taxes payable	713
Equity
Retained earnings	$ 41,091

Acquisitions, Research Collab42

Acquisitions, Research Collaborations and License Agreements - Collaborative Arrangements Narrative (Details) - USD ($) $ in Millions	1 Months Ended				3 Months Ended		35 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2019	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Jan. 31, 2021
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development					$ 3,196	$ 1,830
Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments				$ 750
Research and development					$ 1,400
Eisai | Future Regulatory Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement				385
Eisai | Future Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement				$ 3,970
Eisai | Forecast
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payments to acquire intangible assets	$ 125	$ 200	$ 325				$ 650

Acquisitions, Research Collab43

Acquisitions, Research Collaborations and License Agreements - Acquisitions Narrative (Details) $ / shares in Units, $ in Millions, $ in Millions	1 Months Ended			3 Months Ended
	Feb. 28, 2018AUD ($)$ / shares	Feb. 28, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Mar. 31, 2018USD ($)
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Business acquisition, price per share | $ / shares	$ 1.75
Future consideration to be transferred	$ 502	$ 394
Goodwill				$ 18,284	$ 18,304
Vallee SA
Acquisitions Divestitures Research Collaborations And License Agreements Transactions [Line Items]
Percentage of business acquired (as percent)			93.50%	4.50%
Cash paid for acquisition of business			$ 358
Escrow deposit			176
Intangible assets			297
Deferred tax liabilities noncurrent			102
Other net assets			32
Noncontrolling interest			25
Contingent liabilities			37
Indemnification assets			37
Goodwill			$ 156
Discount rate (as percent)			15.50%
Acquired finite-lived intangible assets, weighted average useful life			15 years
Payments to acquire additional interest in subsidiary				$ 18

Collaborative Arrangements - Na

Collaborative Arrangements - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		12 Months Ended
	Jan. 31, 2018	Jul. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development			$ 3,196	$ 1,830
Accrued and other current liabilities			9,709			$ 10,427
Sales			10,037	$ 9,434
AstraZeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments		$ 1,600
Payments to acquire intangible assets		750				250
Research and development						2,350
Contingent payments collaborative arrangement	$ 70	6,150
Total consideration collaborative arrangement (up to value)		8,500
AstraZeneca | Future Regulatory Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement	$ 1,980	2,050
AstraZeneca | Future Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement		$ 4,100	3,850
AstraZeneca | Lynparza
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accrued and other current liabilities			150			100
Amortization expense for intangible assets			9
AstraZeneca | Lynparza | Forecast
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement					$ 150
Bayer AG | Future Sales-Based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement			775
Bayer AG | Adempas
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments collaborative arrangement			$ 350
Sales						$ 500

Collaborative Arrangements - Sc

Collaborative Arrangements - Schedule of Collaborative Arrangement Transactions (Details) - Collaborative Arrangement - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AstraZeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receivables from counterparty	$ 31
Payables to counterparty	783
AstraZeneca | Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total Sales	33
AstraZeneca | Materials and production
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	12
AstraZeneca | Marketing and administrative
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	7
AstraZeneca | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	29
Bayer AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receivables from counterparty	35
Payables to counterparty	0
Bayer AG | Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Product sales, net	43	$ 31
Profit sharing	25	53
Total Sales	68	84
Bayer AG | Materials and production
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	27	23
Bayer AG | Marketing and administrative
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	8	7
Bayer AG | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	$ 32	$ 22

Restructuring - Narrative (Deta

Restructuring - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)position	Mar. 31, 2017USD ($)position
Restructuring and Related Activities [Abstract]
Total pretax restructuring costs	$ 104	$ 215
Cumulative restructuring costs incurred to date since program inception	$ 13,600
Positions eliminated since inception of program (in positions) | position	44,060
Estimated remaining costs related to restructuring program activities	$ 500
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	710	545

Restructuring - Charges Related

Restructuring - Charges Related to Restructuring Program Activities by Type of Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	$ 104	$ 215
Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	55	84
Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	(2)	49
Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	51	82
Materials and production
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	6	63
Materials and production | Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	0
Materials and production | Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	51
Materials and production | Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	6	12
Marketing and administrative
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	1	1
Marketing and administrative | Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	0
Marketing and administrative | Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	1	0
Marketing and administrative | Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	1
Research and development
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	2	0
Research and development | Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	0
Research and development | Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	(3)	(2)
Research and development | Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	5	2
Restructuring costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	95	151
Restructuring costs | Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	55	84
Restructuring costs | Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	0
Restructuring costs | Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	$ 40	$ 67

Restructuring - Charges and Spe

Restructuring - Charges and Spending Relating to Restructuring Activities by Program (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 747
Expense	104	$ 215
(Payments) receipts, net	(203)
Non-cash activity	3
Restructuring reserve, ending balance	651
Separation Costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	619
Expense	55	84
(Payments) receipts, net	(139)
Non-cash activity	0
Restructuring reserve, ending balance	535
Accelerated Depreciation
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0
Expense	(2)	49
(Payments) receipts, net	0
Non-cash activity	2
Restructuring reserve, ending balance	0
Other
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	128
Expense	51	$ 82
(Payments) receipts, net	(64)
Non-cash activity	1
Restructuring reserve, ending balance	$ 116

Financial Instruments - Narrati

Financial Instruments - Narrative (Details)	3 Months Ended
	Mar. 31, 2018USD ($)interest_rate_swap	Dec. 31, 2017USD ($)
Derivative [Line Items]
Number of interest rate swaps held (in interest rate swaps) | interest_rate_swap	26
Pretax net unrealized loss on derivatives maturing within next 12 months estimated to be reclassified from AOCI to sales	$ 264,000,000
Equity investments without readily determinable fair values	516,000,000
Unrealized gains of equity investments	33,000,000
Impairment losses on investments	8,000,000
Available-for-sale debt securities included in Short-term investments	2,900,000,000
Available-for-sale debt securities maturing after one year through five years	10,600,000,000
Cash and cash equivalents	4,483,000,000	$ 6,092,000,000
Fair value of loans payable and long-term debt, including current portion	24,300,000,000	25,600,000,000
Carrying value of loans payable and long-term debt, including current portion	23,600,000,000	24,400,000,000
Accounts receivable outstanding for more than one year	80,000,000
Cash collateral received from counterparties	0	3,000,000
Cash collateral advanced	0	$ 0
Significant Other Observable Inputs (Level 2)
Derivative [Line Items]
Cash and cash equivalents	4,500,000,000
Cash equivalents	$ 3,500,000,000
Derivatives Designated as Hedging Instruments | Maximum
Derivative [Line Items]
Maximum average period of maturities of contracts in years (less than)	2 years
Derivatives Not Designated as Hedging Instruments | Maximum
Derivative [Line Items]
Maximum average period of maturities of contracts in years (less than)	1 year

Financial Instruments - Effect

Financial Instruments - Effect of Net Investment Hedges (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income	$ (2)	$ 0
Foreign exchange contracts | Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pretax (Gain) Loss Recognized in Income For Amounts Excluded from Effectiveness Testing	0	0
Euro-denominated notes
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income	178	135
Euro-denominated notes | Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pretax (Gain) Loss Recognized in Income For Amounts Excluded from Effectiveness Testing	$ 0	$ 0

Financial Instruments - Summary

Financial Instruments - Summary of Interest Rate Swaps Held (Details)	Mar. 31, 2018USD ($)interest_rate_swap	Dec. 31, 2017USD ($)
Derivative [Line Items]
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap	26
Total Swap Notional Amount	$ 27,650,000,000	$ 25,595,000,000
1.30% notes due 2018 | Interest rate swap contracts
Derivative [Line Items]
Stated interest rate (as percent)	1.30%
Par Value of Debt	$ 1,000,000,000
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap	4
Total Swap Notional Amount	$ 1,000,000,000
5.00% notes due 2019 | Interest rate swap contracts
Derivative [Line Items]
Stated interest rate (as percent)	5.00%
Par Value of Debt	$ 1,250,000,000
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap	3
Total Swap Notional Amount	$ 550,000,000
1.85% notes due 2020 | Interest rate swap contracts
Derivative [Line Items]
Stated interest rate (as percent)	1.85%
Par Value of Debt	$ 1,250,000,000
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap	5
Total Swap Notional Amount	$ 1,250,000,000
3.875% notes due 2021 | Interest rate swap contracts
Derivative [Line Items]
Stated interest rate (as percent)	3.875%
Par Value of Debt	$ 1,150,000,000
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap	5
Total Swap Notional Amount	$ 1,150,000,000
2.40% notes due 2022 | Interest rate swap contracts
Derivative [Line Items]
Stated interest rate (as percent)	2.40%
Par Value of Debt	$ 1,000,000,000
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap	4
Total Swap Notional Amount	$ 1,000,000,000
2.35% notes due 2022 | Interest rate swap contracts
Derivative [Line Items]
Stated interest rate (as percent)	2.35%
Par Value of Debt	$ 1,250,000,000
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap	5
Total Swap Notional Amount	$ 1,250,000,000

Financial Instruments - Fair Va

Financial Instruments - Fair Value Hedges (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Loans payable and current portion of long-term debt
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Assets (Liabilities)	$ (998)	$ (983)
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount	2	17
Long-Term Debt
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Assets (Liabilities)	(5,083)	(5,146)
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount	106	41
Long-Term Debt | Derivatives Not Designated as Hedging Instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount	$ 9	$ 11

Financial Instruments - Fair 53

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	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	$ 109	$ 130
Fair Value of Derivative, Liability	324	217
U.S. Dollar Notional	27,650	25,595
Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	51	91
Fair Value of Derivative, Liability	235	127
U.S. Dollar Notional	15,452	14,386
Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	58	39
Fair Value of Derivative, Liability	89	90
U.S. Dollar Notional	12,198	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	1	3
U.S. Dollar Notional	1,000	1,000
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	114	52
U.S. Dollar Notional	5,200	4,650
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	30	38
U.S. Dollar Notional	2,407	1,936
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other current assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	21	51
U.S. Dollar Notional	3,584	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	119	71
U.S. Dollar Notional	3,205	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	56	20
Foreign exchange contracts | Derivatives Not Designated as Hedging Instruments | Other current assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	58	39
U.S. Dollar Notional	5,434	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	89	90
U.S. Dollar Notional	$ 6,764	$ 7,431

Financial Instruments - Informa

Financial Instruments - Information on Derivative Positions Subject to Master Netting Arrangements as if they were Presented on a Net Basis (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross amounts recognized in the consolidated balance sheet, asset	$ 109,000,000	$ 130,000,000
Gross amount subject to offset in master netting arrangements not offset in the consolidated balance sheet, asset	(103,000,000)	(94,000,000)
Cash collateral received, asset	0	(3,000,000)
Net amounts, asset	6,000,000	33,000,000
Gross amounts recognized in the consolidated balance sheet, liability	324,000,000	217,000,000
Gross amount subject to offset in master netting arrangements not offset in the consolidated balance sheet, liability	(103,000,000)	(94,000,000)
Cash collateral received, liability	0	0
Net amounts, liability	$ 221,000,000	$ 123,000,000

Financial Instruments - Locatio

Financial Instruments - Location and Amount of Pretax (Gains) Losses of Derivatives (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Sales	$ 10,037	$ 9,434
Other (income) expense, net	(291)	(71)
Other comprehensive income (loss)	(124)	(146)
Amount of (loss) recognized in OCI on derivatives	(181)	(263)
Other comprehensive income (loss), reclassifications	93	(94)
Sales
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items	0	0
Derivatives designated as hedging instruments	0	0
Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items	(62)	(16)
Derivatives designated as hedging instruments	62	4
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest
Derivative Instruments, Gain (Loss) [Line Items]
Sales	(93)	94
Other (income) expense, net	$ 0	$ 0

Financial Instruments - Income

Financial Instruments - Income Statement Effects on Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Foreign currency | Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Pretax (Gain) Loss Recognized in Income	$ 28	$ (47)
Forecasted transactions | Sales
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Pretax (Gain) Loss Recognized in Income	$ 8	$ 0

Financial Instruments - Infor57

Financial Instruments - Information on Available-for-sale Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Debt securities, fair value	$ 14,206	$ 14,908
Publicly traded equity securities, fair value	332
Available-for-sale Securities, Equity Securities		275
Total debt and publicly traded equity securities, fair value	14,538
Available-for-sale Securities		15,183
Debt securities, amortized cost	14,374	14,976
Publicly traded equity securities, amortized cost		265
Total debt and publicly traded equity securities, amortized cost		15,241
Debt securities, unrealized gains	4	11
Equity securities, unrealized gains		16
Total debt and publicly traded equity securities, unrealized gains		27
Debt securities, unrealized losses	(172)	(79)
Equity securities, unrealized losses		(6)
Total debt and publicly traded equity securities, unrealized losses		(85)
Unrealized net gain	44
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Debt securities, fair value	130	159
Debt securities, amortized cost	130	159
Debt securities, unrealized gains	0	0
Debt securities, unrealized losses	0	0
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Debt securities, fair value	9,860	9,806
Debt securities, amortized cost	9,978	9,837
Debt securities, unrealized gains	3	9
Debt securities, unrealized losses	(121)	(40)
U.S. government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities, fair value	1,810	2,042
Debt securities, amortized cost	1,833	2,059
Debt securities, unrealized gains	0	0
Debt securities, unrealized losses	(23)	(17)
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities, fair value	1,569	1,542
Debt securities, amortized cost	1,585	1,548
Debt securities, unrealized gains	1	1
Debt securities, unrealized losses	(17)	(7)
Foreign government bonds
Schedule of Available-for-sale Securities [Line Items]
Debt securities, fair value	759	733
Debt securities, amortized cost	769	739
Debt securities, unrealized gains	0	0
Debt securities, unrealized losses	(10)	(6)
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities, fair value	78	626
Debt securities, amortized cost	79	634
Debt securities, unrealized gains	0	1
Debt securities, unrealized losses	$ (1)	$ (9)

Financial Instruments - Financi

Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	$ 14,206	$ 14,908
Investments	332
Assets
Derivative assets	109	130
Liabilities
Contingent consideration	919	935	$ 925	$ 891
Derivative liabilities	324	217
Commercial paper
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	130	159
Corporate notes and bonds
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	9,860	9,806
U.S. government and agency securities
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	1,810	2,042
Asset-backed securities
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	$ 1,569	1,542
Liabilities
Primary weighted average life of collateral	5 years
Foreign government bonds
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	$ 759	733
Mortgage-backed securities
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	78	626
Fair Value, Measurements, Recurring
Assets
Investments	13,896	14,531
Other assets	642	652
Derivative assets	109	130
Total assets	14,647	15,313
Liabilities
Contingent consideration	919	935
Derivative liabilities	324	217
Total liabilities	1,243	1,152
Fair Value, Measurements, Recurring | Purchased currency options
Assets
Derivative assets	46	80
Liabilities
Derivative liabilities	1	0
Fair Value, Measurements, Recurring | Foreign exchange contracts
Assets
Derivative assets	63	48
Liabilities
Derivative liabilities	208	162
Fair Value, Measurements, Recurring | Interest rate swap contracts
Assets
Derivative assets	0	2
Liabilities
Derivative liabilities	115	55
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Investments	164	172
Other assets	232	171
Derivative assets	0	0
Total assets	396	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) | 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) | 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) | Interest rate swap contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets
Investments	13,732	14,359
Other assets	410	481
Derivative assets	109	130
Total assets	14,251	14,970
Liabilities
Contingent consideration	0	0
Derivative liabilities	324	217
Total liabilities	324	217
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Purchased currency options
Assets
Derivative assets	46	80
Liabilities
Derivative liabilities	1	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign exchange contracts
Assets
Derivative assets	63	48
Liabilities
Derivative liabilities	208	162
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swap contracts
Assets
Derivative assets	0	2
Liabilities
Derivative liabilities	115	55
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	919	935
Derivative liabilities	0	0
Total liabilities	919	935
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) | Foreign exchange contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
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 | Commercial paper
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	130	159
Fair Value, Measurements, Recurring | Commercial paper | Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Commercial paper | Significant Other Observable Inputs (Level 2)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	130	159
Fair Value, Measurements, Recurring | Commercial paper | Significant Unobservable Inputs (Level 3)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Corporate notes and bonds
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	9,741	9,678
Assets
Other assets	119	128
Fair Value, Measurements, Recurring | Corporate notes and bonds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Corporate notes and bonds | Significant Other Observable Inputs (Level 2)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	9,741	9,678
Assets
Other assets	119	128
Fair Value, Measurements, Recurring | Corporate notes and bonds | Significant Unobservable Inputs (Level 3)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | U.S. government and agency securities
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	1,585	1,835
Assets
Other assets	225	207
Fair Value, Measurements, Recurring | U.S. government and agency securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	68
Assets
Other assets	64	0
Fair Value, Measurements, Recurring | U.S. government and agency securities | Significant Other Observable Inputs (Level 2)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	1,585	1,767
Assets
Other assets	161	207
Fair Value, Measurements, Recurring | U.S. government and agency securities | Significant Unobservable Inputs (Level 3)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Asset-backed securities
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	1,517	1,476
Assets
Other assets	52	66
Fair Value, Measurements, Recurring | Asset-backed securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Asset-backed securities | Significant Other Observable Inputs (Level 2)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	1,517	1,476
Assets
Other assets	52	66
Fair Value, Measurements, Recurring | Asset-backed securities | Significant Unobservable Inputs (Level 3)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Foreign government bonds
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	759	732
Assets
Other assets	0	1
Fair Value, Measurements, Recurring | Foreign government bonds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Foreign government bonds | Significant Other Observable Inputs (Level 2)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	759	732
Assets
Other assets	0	1
Fair Value, Measurements, Recurring | Foreign government bonds | Significant Unobservable Inputs (Level 3)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Mortgage-backed securities
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	547
Assets
Other assets	78	79
Fair Value, Measurements, Recurring | Mortgage-backed securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	547
Assets
Other assets	78	79
Fair Value, Measurements, Recurring | Mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Publicly traded equity securities
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	164	104
Assets
Other assets	168	171
Fair Value, Measurements, Recurring | Publicly traded equity securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	164	104
Assets
Other assets	168	171
Fair Value, Measurements, Recurring | Publicly traded equity securities | Significant Other Observable Inputs (Level 2)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Publicly traded equity securities | Significant Unobservable Inputs (Level 3)
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items]
Investments	0	0
Assets
Other assets	$ 0	$ 0

Financial Instruments - Infor59

Financial Instruments - Information About Changes in Liabilities for Contingent Consideration (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 935	$ 891
Changes in fair value	36	34
Additions	8	0
Payments	(60)	0
Fair value, ending balance	919	$ 925
Current liability	$ 337

Inventories - Narrative (Detail

Inventories - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
Inventories classified in Other assets	$ 1,136	$ 1,187
Inventories Not Expected to be Sold Within One Year
Inventory [Line Items]
Inventories classified in Other assets	1,100	1,100
Inventories Produced in Preparation for Product Launches
Inventory [Line Items]
Inventories classified in Other assets	$ 18	$ 80

Inventories - Inventories (Deta

Inventories - Inventories (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Finished goods	$ 1,530	$ 1,334
Raw materials and work in process	4,764	4,703
Supplies	199	201
Total (approximates current cost)	6,493	6,238
Increase to LIFO costs	25	45
Total current and noncurrent inventories	6,518	6,283
Recognized as:
Inventories	5,382	5,096
Other Assets	$ 1,136	$ 1,187

Contingencies - Fosamax Litigat

Contingencies - Fosamax Litigation - Narrative (Details) - Fosamax $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2014legalmatter	Mar. 31, 2018legalmatter	Dec. 31, 2014USD ($)	Jul. 31, 2015legalmatter	Nov. 30, 2013legalmatter
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		4,040
ONJ Litigation
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		10
Litigation settlement amount to other party | $			$ 27.3
Percentage of participation in litigation settlement (as percent)			95.00%
Femur Fracture Litigation
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		4,030
Femur Fracture Litigation | Federal
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		540
Loss contingency, claims dismissed, number (in legal matters)	650	510
Loss contingency, claims on appeal, number (in legal matters)		515
Femur Fracture Litigation | New Jersey state court
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		2,700
Loss contingency, initial cases selected for review, number (in legal matters)		30
Loss contingency, subsequent cases selected for review, number (in legal matters)	50			25	50
Femur Fracture Litigation | California state court
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		280
Loss contingency, initial cases selected for review, number (in legal matters)	10
Femur Fracture Litigation | Other state courts
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		4

Contingencies - Januvia_Janumet

Contingencies - Januvia/Janumet Litigation - Narrative (Details) - Januvia - legalmatter	1 Months Ended
	Nov. 30, 2015	Mar. 31, 2018
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		1,245
Loss contingency, claims dismissed, number (in legal matters)	1,100
Cases Company Agreed To Toll Statute Of Limitations
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		50
Other state courts
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		7
Other state courts | Illinois state court
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		4

Contingencies - Propecia_Prosca

Contingencies - Propecia/Proscar Litigation - Narrative (Details) - Propecia/Proscar $ in Millions	Apr. 09, 2018USD ($)	Mar. 31, 2018Plaintifflegalmatter
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		600
Subsequent event
Loss Contingencies [Line Items]
Percentage of participation in litigation settlement (as percent)	95.00%
Litigation settlement amount to other party | $	$ 4.3
Cases alleging cancer
Loss Contingencies [Line Items]
Number of plaintiffs | Plaintiff		15
Other state courts | California state court
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		1
Other state courts | Ohio state court
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		1
Other state courts | Massachusetts state court
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		1

Contingencies - Patent Litigati

Contingencies - Patent Litigation - Narrative (Details) - USD ($) $ in Millions	1 Months Ended
	Jan. 31, 2018	Dec. 31, 2016	Mar. 31, 2016
Loss Contingencies [Line Items]
Gain on settlement	$ 115
Gilead Patent Case
Loss Contingencies [Line Items]
Amount awarded to company		$ 2,540	$ 200

Contingencies - Legal Defense R

Contingencies - Legal Defense Reserves - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Legal Defense Costs
Loss Contingencies [Line Items]
Legal defense costs reserve	$ 155	$ 160

Contingencies - Environmental -

Contingencies - Environmental - Narrative (Details) € in Thousands, $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2018USD ($)	Mar. 31, 2018USD ($)	Mar. 31, 2018EUR (€)
Loss Contingencies [Line Items]
Loss on settlement	$ (115,000)
Oss Netherlands
Loss Contingencies [Line Items]
Fine for alleged environmental violation		$ 235
Loss on settlement | €			€ 400

Equity - Shareholders' Equity (

Equity - Shareholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, beginning balance (in shares)	3,577,103,522
Equity, beginning balance	$ 34,569	$ 40,308
Adoption of new accounting standards			$ 48
Net income attributable to Merck & Co., Inc.	736	1,551
Other comprehensive income (loss), net of taxes	124	146
Cash dividends declared on common stock	(1,301)	(1,297)
Treasury stock shares purchased	(566)	(1,019)
Share-based compensation plans and other	291	368
Acquisition of Vallée		25
Net income attributable to noncontrolling interests	5	5
Distributions attributable to noncontrolling interests	$ (5)
Other changes in noncontrolling ownership interests		1
Shares, ending balance (in shares)	3,577,103,522
Equity, ending balance	$ 33,901	$ 40,088
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, beginning balance (in shares)	3,577,000,000	3,577,000,000
Equity, beginning balance	$ 1,788	$ 1,788
Shares, ending balance (in shares)	3,577,000,000	3,577,000,000
Equity, ending balance	$ 1,788	$ 1,788
Other Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	39,902	39,939
Share-based compensation plans and other	(28)	(40)
Equity, ending balance	39,874	39,899
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	41,350	44,133
Adoption of new accounting standards			322
Net income attributable to Merck & Co., Inc.	736	1,551
Cash dividends declared on common stock	(1,301)	(1,297)
Equity, ending balance	41,107	44,387
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	(4,910)	(5,226)
Adoption of new accounting standards			$ (274)
Other comprehensive income (loss), net of taxes	124	146
Equity, ending balance	$ (5,060)	$ (5,080)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, beginning balance (in shares)	880,000,000	828,000,000
Equity, beginning balance	$ (43,794)	$ (40,546)
Treasury stock shares purchased (in shares)	10,000,000	16,000,000
Treasury stock shares purchased	$ (566)	$ (1,019)
Share-based compensation plans and other (in shares)	(5,000,000)	(7,000,000)
Share-based compensation plans and other	$ 319	$ 408
Shares, ending balance (in shares)	885,000,000	837,000,000
Equity, ending balance	$ (44,041)	$ (41,157)
Non- Controlling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	233	220
Acquisition of Vallée		25
Net income attributable to noncontrolling interests	5	5
Distributions attributable to noncontrolling interests	(5)
Other changes in noncontrolling ownership interests		1
Equity, ending balance	$ 233	$ 251

Share-Based Compensation Plan69

Share-Based Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
RSUs granted (in shares)	121	86
Weighted-average fair value per RSU granted (in dollars per share)	$ 55.88	$ 64.20
Options granted (in shares)	46	190
Weighted- average exercise price of options granted in period (in dollars per share)	$ 55.88	$ 64.20
Weighted- average fair value per option granted (in dollars per share)	$ 7.83	$ 7.89
Total pretax unrecognized compensation expense related to nonvested stock options	$ 798
Weighted average period in years of recognition for nonvested stock options	2 years 4 months 24 days

Share-Based Compensation Plan70

Share-Based Compensation Plans - Amounts of Share-Based Compensation Cost Recorded in Consolidated Statement of Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Pretax share-based compensation expense	$ 80	$ 74
Income tax benefit	(15)	(22)
Total share-based compensation expense, net of taxes	$ 65	$ 52

Share-Based Compensation Plan71

Share-Based Compensation Plans - Assumptions Used to Determine Weighted-Average Fair Value of Options Granted (Details)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected dividend yield	3.40%	3.70%
Risk-free interest rate	2.70%	2.00%
Expected volatility	19.50%	19.70%
Expected life (years)	6 years	6 years 2 months 12 days

Pension and Other Postretirem72

Pension and Other Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 14	$ 14
Interest cost	18	20
Expected return on plan assets	(21)	(19)
Amortization of unrecognized prior service credit	(21)	(25)
Termination benefits	1	1
Curtailments	(4)	(3)
Net periodic benefit cost	(13)	(12)
U.S. | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	83	77
Interest cost	108	113
Expected return on plan assets	(214)	(218)
Amortization of unrecognized prior service credit	(13)	(13)
Net loss amortization	56	44
Termination benefits	11	5
Curtailments	(2)	3
Settlements	1	0
Net periodic benefit cost	30	11
International | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	67	61
Interest cost	46	41
Expected return on plan assets	(113)	(94)
Amortization of unrecognized prior service credit	(3)	(2)
Net loss amortization	21	23
Termination benefits	0	1
Curtailments	0	0
Settlements	0	0
Net periodic benefit cost	$ 18	$ 30

Other (Income) Expense, Net (De

Other (Income) Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Income and Expenses [Abstract]
Interest income	$ (85)	$ (97)
Interest expense	185	182
Exchange losses (gains)	7	(8)
Equity losses from affiliates	52	13
Net periodic defined benefit plan (credit) cost other than service cost	(135)	(129)
Other, net	(315)	(32)
Other (income) expense, net	$ (291)	$ (71)

Other (Income) Expense, Net - N

Other (Income) Expense, Net - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Other Income and Expenses [Abstract]
Gain on settlement	$ 115
Interest paid		$ 186	$ 162

Taxes on Income - Narrative (De

Taxes on Income - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Examination [Line Items]
Effective income tax rate (as percent)	44.90%	22.30%
Research and development	$ 3,196	$ 1,830
Transition tax liability			$ 5,300
Net transition tax payment			5,100
Provisional deferred tax benefit			779
2017 Tax Cuts and Jobs Act (TCJA)
Income Tax Examination [Line Items]
Deferred taxes			$ 2,000
Eisai
Income Tax Examination [Line Items]
Research and development	$ 1,400

Earnings Per Share - Calculatio

Earnings Per Share - Calculations of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to Merck & Co., Inc.	$ 736	$ 1,551
Average common shares outstanding (in shares)	2,695	2,745
Common shares issuable (in shares)	15	21
Average common shares outstanding assuming dilution (in shares)	2,710	2,766
Basic earnings per common share attributable to Merck & Co., Inc. common shareholders (in dollars per share)	$ 0.27	$ 0.56
Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders (in dollars per share)	$ 0.27	$ 0.56

Earnings Per Share - Narrative

Earnings Per Share - Narrative (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
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 (in shares)	14	2

Other Comprehensive Income (L78

Other Comprehensive Income (Loss) - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	$ 34,569	$ 40,308
Other comprehensive income (loss) before reclassification adjustments, pretax	25	83
Tax	(21)	140
Other comprehensive income (loss) before reclassification adjustments, net of taxes	4	223
Reclassification adjustments, pretax	145	(124)
Tax	(25)	47
Reclassification adjustments, net of taxes	120	(77)
Other comprehensive income (loss), net of taxes	124	146
Reclassification of provisional stranded tax effects	(266)
Adoption of ASU 2016-01			$ (8)
Equity, ending balance	33,901	40,088
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(108)	338
Other comprehensive income (loss) before reclassification adjustments, pretax	(181)	(263)
Tax	38	92
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(143)	(171)
Reclassification adjustments, pretax	92	(95)
Tax	(19)	34
Reclassification adjustments, net of taxes	73	(61)
Other comprehensive income (loss), net of taxes	(70)	(232)
Reclassification of provisional stranded tax effects	(23)
Adoption of ASU 2016-01			0
Equity, ending balance	(201)	106
Investments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(61)	(3)
Other comprehensive income (loss) before reclassification adjustments, pretax	(112)	87
Tax	0	(7)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(112)	80
Reclassification adjustments, pretax	12	(57)
Tax	1	20
Reclassification adjustments, net of taxes	13	(37)
Other comprehensive income (loss), net of taxes	(99)	43
Reclassification of provisional stranded tax effects	1
Adoption of ASU 2016-01			(8)
Equity, ending balance	(167)	40
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(2,787)	(3,206)
Other comprehensive income (loss) before reclassification adjustments, pretax	(1)	(4)
Tax	3	9
Other comprehensive income (loss) before reclassification adjustments, net of taxes	2	5
Reclassification adjustments, pretax	41	28
Tax	(7)	(7)
Reclassification adjustments, net of taxes	34	21
Other comprehensive income (loss), net of taxes	36	26
Reclassification of provisional stranded tax effects	(344)
Adoption of ASU 2016-01			0
Equity, ending balance	(3,095)	(3,180)
Cumulative Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(1,954)	(2,355)
Other comprehensive income (loss) before reclassification adjustments, pretax	319	263
Tax	(62)	46
Other comprehensive income (loss) before reclassification adjustments, net of taxes	257	309
Reclassification adjustments, pretax	0	0
Tax	0	0
Reclassification adjustments, net of taxes	0	0
Other comprehensive income (loss), net of taxes	257	309
Reclassification of provisional stranded tax effects	100
Adoption of ASU 2016-01			$ 0
Equity, ending balance	(1,597)	(2,046)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(4,910)	(5,226)
Equity, ending balance	$ (5,060)	$ (5,080)

Segment Reporting - Narrative (

Segment Reporting - Narrative (Details)	3 Months Ended
	Mar. 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	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Sales	$ 10,037	$ 9,434
Proceeds from sale of marketing rights	21	50
Operating Segments
Segment Reporting Information [Line Items]
Sales	10,068	9,218
Operating Segments | Total Pharmaceutical segment sales
Segment Reporting Information [Line Items]
Sales	8,919	8,185
Operating Segments | Total Pharmaceutical segment sales | Keytruda
Segment Reporting Information [Line Items]
Sales	1,464	584
Operating Segments | Total Pharmaceutical segment sales | Emend
Segment Reporting Information [Line Items]
Sales	125	133
Operating Segments | Total Pharmaceutical segment sales | Temodar
Segment Reporting Information [Line Items]
Sales	57	66
Operating Segments | Total Pharmaceutical segment sales | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	33	0
Operating Segments | Total Pharmaceutical segment sales | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	660	532
Operating Segments | Total Pharmaceutical segment sales | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	392	355
Operating Segments | Total Pharmaceutical segment sales | RotaTeq
Segment Reporting Information [Line Items]
Sales	193	224
Operating Segments | Total Pharmaceutical segment sales | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	179	163
Operating Segments | Total Pharmaceutical segment sales | Zostavax
Segment Reporting Information [Line Items]
Sales	65	154
Operating Segments | Total Pharmaceutical segment sales | Bridion
Segment Reporting Information [Line Items]
Sales	204	148
Operating Segments | Total Pharmaceutical segment sales | Noxafil
Segment Reporting Information [Line Items]
Sales	176	141
Operating Segments | Total Pharmaceutical segment sales | Invanz
Segment Reporting Information [Line Items]
Sales	151	136
Operating Segments | Total Pharmaceutical segment sales | Cubicin
Segment Reporting Information [Line Items]
Sales	98	96
Operating Segments | Total Pharmaceutical segment sales | Cancidas
Segment Reporting Information [Line Items]
Sales	91	121
Operating Segments | Total Pharmaceutical segment sales | Primaxin
Segment Reporting Information [Line Items]
Sales	72	62
Operating Segments | Total Pharmaceutical segment sales | Simponi
Segment Reporting Information [Line Items]
Sales	231	184
Operating Segments | Total Pharmaceutical segment sales | Remicade
Segment Reporting Information [Line Items]
Sales	167	229
Operating Segments | Total Pharmaceutical segment sales | Belsomra
Segment Reporting Information [Line Items]
Sales	54	42
Operating Segments | Total Pharmaceutical segment sales | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	281	305
Operating Segments | Total Pharmaceutical segment sales | Zepatier
Segment Reporting Information [Line Items]
Sales	131	378
Operating Segments | Total Pharmaceutical segment sales | Zetia
Segment Reporting Information [Line Items]
Sales	305	334
Operating Segments | Total Pharmaceutical segment sales | Vytorin
Segment Reporting Information [Line Items]
Sales	167	241
Operating Segments | Total Pharmaceutical segment sales | Atozet
Segment Reporting Information [Line Items]
Sales	73	49
Operating Segments | Total Pharmaceutical segment sales | Adempas
Segment Reporting Information [Line Items]
Sales	68	84
Operating Segments | Total Pharmaceutical segment sales | Januvia
Segment Reporting Information [Line Items]
Sales	880	839
Operating Segments | Total Pharmaceutical segment sales | Janumet
Segment Reporting Information [Line Items]
Sales	544	496
Operating Segments | Total Pharmaceutical segment sales | NuvaRing
Segment Reporting Information [Line Items]
Sales	216	160
Operating Segments | Total Pharmaceutical segment sales | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	174	170
Operating Segments | Total Pharmaceutical segment sales | Singulair
Segment Reporting Information [Line Items]
Sales	175	186
Operating Segments | Total Pharmaceutical segment sales | Nasonex
Segment Reporting Information [Line Items]
Sales	122	139
Operating Segments | Total Pharmaceutical segment sales | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	120	112
Operating Segments | Total Pharmaceutical segment sales | Arcoxia
Segment Reporting Information [Line Items]
Sales	83	103
Operating Segments | Total Pharmaceutical segment sales | Follistim AQ
Segment Reporting Information [Line Items]
Sales	67	81
Operating Segments | Total Pharmaceutical segment sales | Dulera
Segment Reporting Information [Line Items]
Sales	57	82
Operating Segments | Total Pharmaceutical segment sales | Fosamax
Segment Reporting Information [Line Items]
Sales	55	61
Operating Segments | Total Pharmaceutical segment sales | Other Pharmaceutical
Segment Reporting Information [Line Items]
Sales	989	995
Operating Segments | Total Animal Health segment sales
Segment Reporting Information [Line Items]
Sales	1,065	939
Operating Segments | Total Animal Health segment sales | Livestock
Segment Reporting Information [Line Items]
Sales	652	578
Operating Segments | Total Animal Health segment sales | Companion Animals
Segment Reporting Information [Line Items]
Sales	413	361
Operating Segments | Other segment sales
Segment Reporting Information [Line Items]
Sales	84	94
Other
Segment Reporting Information [Line Items]
Sales	(31)	216
United States
Segment Reporting Information [Line Items]
Sales	4,133	4,195
United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	4,107	4,138
United States | Operating Segments | Total Pharmaceutical segment sales
Segment Reporting Information [Line Items]
Sales	3,716	3,761
United States | Operating Segments | Total Pharmaceutical segment sales | Keytruda
Segment Reporting Information [Line Items]
Sales	838	361
United States | Operating Segments | Total Pharmaceutical segment sales | Emend
Segment Reporting Information [Line Items]
Sales	79	86
United States | Operating Segments | Total Pharmaceutical segment sales | Temodar
Segment Reporting Information [Line Items]
Sales	1	1
United States | Operating Segments | Total Pharmaceutical segment sales | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	24	0
United States | Operating Segments | Total Pharmaceutical segment sales | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	380	398
United States | Operating Segments | Total Pharmaceutical segment sales | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	312	298
United States | Operating Segments | Total Pharmaceutical segment sales | RotaTeq
Segment Reporting Information [Line Items]
Sales	151	178
United States | Operating Segments | Total Pharmaceutical segment sales | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	112	114
United States | Operating Segments | Total Pharmaceutical segment sales | Zostavax
Segment Reporting Information [Line Items]
Sales	16	109
United States | Operating Segments | Total Pharmaceutical segment sales | Bridion
Segment Reporting Information [Line Items]
Sales	80	45
United States | Operating Segments | Total Pharmaceutical segment sales | Noxafil
Segment Reporting Information [Line Items]
Sales	81	65
United States | Operating Segments | Total Pharmaceutical segment sales | Invanz
Segment Reporting Information [Line Items]
Sales	91	82
United States | Operating Segments | Total Pharmaceutical segment sales | Cubicin
Segment Reporting Information [Line Items]
Sales	47	54
United States | Operating Segments | Total Pharmaceutical segment sales | Cancidas
Segment Reporting Information [Line Items]
Sales	3	5
United States | Operating Segments | Total Pharmaceutical segment sales | Primaxin
Segment Reporting Information [Line Items]
Sales	5	0
United States | Operating Segments | Total Pharmaceutical segment sales | Simponi
Segment Reporting Information [Line Items]
Sales	0	0
United States | Operating Segments | Total Pharmaceutical segment sales | Remicade
Segment Reporting Information [Line Items]
Sales	0	0
United States | Operating Segments | Total Pharmaceutical segment sales | Belsomra
Segment Reporting Information [Line Items]
Sales	23	20
United States | Operating Segments | Total Pharmaceutical segment sales | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	128	143
United States | Operating Segments | Total Pharmaceutical segment sales | Zepatier
Segment Reporting Information [Line Items]
Sales	0	200
United States | Operating Segments | Total Pharmaceutical segment sales | Zetia
Segment Reporting Information [Line Items]
Sales	17	111
United States | Operating Segments | Total Pharmaceutical segment sales | Vytorin
Segment Reporting Information [Line Items]
Sales	8	90
United States | Operating Segments | Total Pharmaceutical segment sales | Atozet
Segment Reporting Information [Line Items]
Sales	0	0
United States | Operating Segments | Total Pharmaceutical segment sales | Adempas
Segment Reporting Information [Line Items]
Sales	0	0
United States | Operating Segments | Total Pharmaceutical segment sales | Januvia
Segment Reporting Information [Line Items]
Sales	465	507
United States | Operating Segments | Total Pharmaceutical segment sales | Janumet
Segment Reporting Information [Line Items]
Sales	192	195
United States | Operating Segments | Total Pharmaceutical segment sales | NuvaRing
Segment Reporting Information [Line Items]
Sales	171	113
United States | Operating Segments | Total Pharmaceutical segment sales | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	128	132
United States | Operating Segments | Total Pharmaceutical segment sales | Singulair
Segment Reporting Information [Line Items]
Sales	6	6
United States | Operating Segments | Total Pharmaceutical segment sales | Nasonex
Segment Reporting Information [Line Items]
Sales	1	18
United States | Operating Segments | Total Pharmaceutical segment sales | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	7	3
United States | Operating Segments | Total Pharmaceutical segment sales | Arcoxia
Segment Reporting Information [Line Items]
Sales	0	0
United States | Operating Segments | Total Pharmaceutical segment sales | Follistim AQ
Segment Reporting Information [Line Items]
Sales	29	42
United States | Operating Segments | Total Pharmaceutical segment sales | Dulera
Segment Reporting Information [Line Items]
Sales	50	75
United States | Operating Segments | Total Pharmaceutical segment sales | Fosamax
Segment Reporting Information [Line Items]
Sales	(2)	1
United States | Operating Segments | Total Pharmaceutical segment sales | Other Pharmaceutical
Segment Reporting Information [Line Items]
Sales	273	309
United States | Operating Segments | Total Animal Health segment sales
Segment Reporting Information [Line Items]
Sales	307	283
United States | Operating Segments | Total Animal Health segment sales | Livestock
Segment Reporting Information [Line Items]
Sales	124	119
United States | Operating Segments | Total Animal Health segment sales | Companion Animals
Segment Reporting Information [Line Items]
Sales	183	164
United States | Operating Segments | Other segment sales
Segment Reporting Information [Line Items]
Sales	84	94
United States | Other
Segment Reporting Information [Line Items]
Sales	26	57
International
Segment Reporting Information [Line Items]
Sales	5,904	5,239
International | Operating Segments
Segment Reporting Information [Line Items]
Sales	5,960	5,080
International | Operating Segments | Total Pharmaceutical segment sales
Segment Reporting Information [Line Items]
Sales	5,202	4,424
International | Operating Segments | Total Pharmaceutical segment sales | Keytruda
Segment Reporting Information [Line Items]
Sales	626	223
International | Operating Segments | Total Pharmaceutical segment sales | Emend
Segment Reporting Information [Line Items]
Sales	46	47
International | Operating Segments | Total Pharmaceutical segment sales | Temodar
Segment Reporting Information [Line Items]
Sales	56	65
International | Operating Segments | Total Pharmaceutical segment sales | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	9	0
International | Operating Segments | Total Pharmaceutical segment sales | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	280	134
International | Operating Segments | Total Pharmaceutical segment sales | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	80	57
International | Operating Segments | Total Pharmaceutical segment sales | RotaTeq
Segment Reporting Information [Line Items]
Sales	42	45
International | Operating Segments | Total Pharmaceutical segment sales | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	66	49
International | Operating Segments | Total Pharmaceutical segment sales | Zostavax
Segment Reporting Information [Line Items]
Sales	48	45
International | Operating Segments | Total Pharmaceutical segment sales | Bridion
Segment Reporting Information [Line Items]
Sales	124	102
International | Operating Segments | Total Pharmaceutical segment sales | Noxafil
Segment Reporting Information [Line Items]
Sales	94	76
International | Operating Segments | Total Pharmaceutical segment sales | Invanz
Segment Reporting Information [Line Items]
Sales	60	54
International | Operating Segments | Total Pharmaceutical segment sales | Cubicin
Segment Reporting Information [Line Items]
Sales	51	41
International | Operating Segments | Total Pharmaceutical segment sales | Cancidas
Segment Reporting Information [Line Items]
Sales	88	116
International | Operating Segments | Total Pharmaceutical segment sales | Primaxin
Segment Reporting Information [Line Items]
Sales	67	62
International | Operating Segments | Total Pharmaceutical segment sales | Simponi
Segment Reporting Information [Line Items]
Sales	231	184
International | Operating Segments | Total Pharmaceutical segment sales | Remicade
Segment Reporting Information [Line Items]
Sales	167	229
International | Operating Segments | Total Pharmaceutical segment sales | Belsomra
Segment Reporting Information [Line Items]
Sales	31	21
International | Operating Segments | Total Pharmaceutical segment sales | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	152	162
International | Operating Segments | Total Pharmaceutical segment sales | Zepatier
Segment Reporting Information [Line Items]
Sales	131	178
International | Operating Segments | Total Pharmaceutical segment sales | Zetia
Segment Reporting Information [Line Items]
Sales	287	222
International | Operating Segments | Total Pharmaceutical segment sales | Vytorin
Segment Reporting Information [Line Items]
Sales	158	151
International | Operating Segments | Total Pharmaceutical segment sales | Atozet
Segment Reporting Information [Line Items]
Sales	73	49
International | Operating Segments | Total Pharmaceutical segment sales | Adempas
Segment Reporting Information [Line Items]
Sales	68	84
International | Operating Segments | Total Pharmaceutical segment sales | Januvia
Segment Reporting Information [Line Items]
Sales	416	332
International | Operating Segments | Total Pharmaceutical segment sales | Janumet
Segment Reporting Information [Line Items]
Sales	352	302
International | Operating Segments | Total Pharmaceutical segment sales | NuvaRing
Segment Reporting Information [Line Items]
Sales	46	47
International | Operating Segments | Total Pharmaceutical segment sales | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	46	39
International | Operating Segments | Total Pharmaceutical segment sales | Singulair
Segment Reporting Information [Line Items]
Sales	170	180
International | Operating Segments | Total Pharmaceutical segment sales | Nasonex
Segment Reporting Information [Line Items]
Sales	121	121
International | Operating Segments | Total Pharmaceutical segment sales | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	113	109
International | Operating Segments | Total Pharmaceutical segment sales | Arcoxia
Segment Reporting Information [Line Items]
Sales	83	103
International | Operating Segments | Total Pharmaceutical segment sales | Follistim AQ
Segment Reporting Information [Line Items]
Sales	39	40
International | Operating Segments | Total Pharmaceutical segment sales | Dulera
Segment Reporting Information [Line Items]
Sales	7	7
International | Operating Segments | Total Pharmaceutical segment sales | Fosamax
Segment Reporting Information [Line Items]
Sales	57	60
International | Operating Segments | Total Pharmaceutical segment sales | Other Pharmaceutical
Segment Reporting Information [Line Items]
Sales	717	688
International | Operating Segments | Total Animal Health segment sales
Segment Reporting Information [Line Items]
Sales	758	656
International | Operating Segments | Total Animal Health segment sales | Livestock
Segment Reporting Information [Line Items]
Sales	529	459
International | Operating Segments | Total Animal Health segment sales | Companion Animals
Segment Reporting Information [Line Items]
Sales	229	197
International | Operating Segments | Other segment sales
Segment Reporting Information [Line Items]
Sales	0	0
International | Other
Segment Reporting Information [Line Items]
Sales	$ (56)	$ 159

Segment Reporting - Consolidate

Segment Reporting - Consolidated Revenues by Geographic Area (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue from External Customer [Line Items]
Sales	$ 10,037	$ 9,434
United States
Revenue from External Customer [Line Items]
Sales	4,133	4,195
Europe, Middle East, Africa
Revenue from External Customer [Line Items]
Sales	3,191	2,629
Asia Pacific
Revenue from External Customer [Line Items]
Sales	1,238	1,001
Japan
Revenue from External Customer [Line Items]
Sales	737	705
Latin America
Revenue from External Customer [Line Items]
Sales	532	485
Other
Revenue from External Customer [Line Items]
Sales	$ 206	$ 419

Segment Reporting - Reconciliat

Segment Reporting - Reconciliation of Segment Profits to Income Before Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Profits	$ 1,345	$ 2,003
Interest income	85	97
Interest expense	(185)	(182)
Equity income from affiliates	(52)	(13)
Depreciation and amortization	(1,137)	(1,193)
Research and development	(3,196)	(1,830)
Restructuring costs	(95)	(151)
Total segment profits
Segment Reporting Information [Line Items]
Profits	6,280	5,610
Total segment profits | Pharmaceutical segment
Segment Reporting Information [Line Items]
Profits	5,804	5,160
Total segment profits | Animal Health segment
Segment Reporting Information [Line Items]
Profits	413	417
Total segment profits | Other segments
Segment Reporting Information [Line Items]
Profits	63	33
Other profits
Segment Reporting Information [Line Items]
Profits	(87)	142
Unallocated
Segment Reporting Information [Line Items]
Interest income	85	97
Interest expense	(185)	(182)
Equity income from affiliates	(50)	(12)
Depreciation and amortization	(350)	(370)
Research and development	(2,982)	(1,632)
Amortization of purchase accounting adjustments	(733)	(778)
Restructuring costs	(95)	(151)
Other unallocated, net	$ (538)	$ (721)