Merck & Co. (MRK) 10-Q 5 Nov 19 2019 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2019	Oct. 31, 2019
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	1-6571
Entity Registrant Name	Merck & Co., Inc.
Entity Incorporation, State or Country Code	NJ
Entity Tax Identification Number	22-1918501
Entity Address, Address Line One	2000 Galloping Hill Road
Entity Address, City or Town	Kenilworth
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	07033
City Area Code	(908)
Local Phone Number	740-4000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		2,545,984,142
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Central Index Key	0000310158
Current Fiscal Year End Date	--12-31
Common Stock
Entity Information [Line Items]
Title of 12(b) Security	Common Stock ($0.50 par value)
Trading Symbol	MRK
Security Exchange Name	NYSE
1.125% Notes due 2021
Entity Information [Line Items]
Title of 12(b) Security	1.125% Notes due 2021
Trading Symbol	MRK/21
Security Exchange Name	NYSE
0.500% Notes due 2024
Entity Information [Line Items]
Title of 12(b) Security	0.500% Notes due 2024
Trading Symbol	MRK 24
Security Exchange Name	NYSE
1.875% Notes due 2026
Entity Information [Line Items]
Title of 12(b) Security	1.875% Notes due 2026
Trading Symbol	MRK/26
Security Exchange Name	NYSE
2.500% Notes due 2034
Entity Information [Line Items]
Title of 12(b) Security	2.500% Notes due 2034
Trading Symbol	MRK/34
Security Exchange Name	NYSE
1.375% Notes due 2036
Entity Information [Line Items]
Title of 12(b) Security	1.375% Notes due 2036
Trading Symbol	MRK 36A
Security Exchange Name	NYSE

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENT OF INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Sales	$ 12,397	$ 10,794	$ 34,972	$ 31,296
Costs, Expenses and Other
Cost of sales	3,990	3,619	10,443	10,220
Selling, general and administrative	2,589	2,443	7,726	7,459
Research and development	3,204	2,068	7,324	7,538
Restructuring costs	232	171	444	494
Other (income) expense, net	35	(172)	362	(512)
Total Costs, Expenses and Other	10,050	8,129	26,299	25,199
Income Before Taxes	2,347	2,665	8,673	6,097
Taxes on Income	440	707	1,259	1,682
Net Income	1,907	1,958	7,414	4,415
Less: Net Income (Loss) Attributable to Noncontrolling Interests	6	8	(73)	22
Net Income Attributable to Merck & Co., Inc.	$ 1,901	$ 1,950	$ 7,487	$ 4,393
Basic Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 0.74	$ 0.73	$ 2.91	$ 1.64
Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 0.74	$ 0.73	$ 2.89	$ 1.63

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net Income Attributable to Merck & Co., Inc.	$ 1,901	$ 1,950	$ 7,487	$ 4,393
Other Comprehensive (Loss) Income Net of Taxes:
Net unrealized gain (loss) on derivatives, net of reclassifications	91	27	(9)	223
Net unrealized (loss) gain on investments, net of reclassifications	(17)	40	109	(56)
Benefit plan net gain and prior service credit, net of amortization	15	40	41	106
Cumulative translation adjustment	(117)	(136)	14	(240)
Other comprehensive income (loss), net of taxes	(28)	(29)	155	33
Comprehensive Income Attributable to Merck & Co., Inc.	$ 1,873	$ 1,921	$ 7,642	$ 4,426

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEET - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Current Assets
Cash and cash equivalents	$ 7,869	$ 7,965
Short-term investments	149	899
Accounts receivable (net of allowance for doubtful accounts of $116 in 2019 and $119 in 2018)	8,442	7,071
Inventories (excludes inventories of $1,515 in 2019 and $1,417 in 2018 classified in Other assets - see Note 6)	5,855	5,440
Other current assets	3,827	4,500
Total current assets	26,142	25,875
Investments	2,111	6,233
Property, Plant and Equipment, at cost, net of accumulated depreciation of $17,281 in 2019 and $16,324 in 2018	14,287	13,291
Goodwill	19,480	18,253
Other Intangibles, Net	12,307	11,431
Other Assets	9,004	7,554
Total Assets	83,331	82,637
Current Liabilities
Loans payable and current portion of long-term debt	3,411	5,308
Trade accounts payable	3,198	3,318
Accrued and other current liabilities	11,768	10,151
Income taxes payable	873	1,971
Dividends payable	1,434	1,458
Total current liabilities	20,684	22,206
Long-Term Debt	22,677	19,806
Deferred Income Taxes	1,960	1,702
Other Noncurrent Liabilities	11,085	12,041
Merck & Co., Inc. Stockholders’ Equity
Common stock, $0.50 par value Authorized - 6,500,000,000 shares Issued - 3,577,103,522 shares in 2019 and 2018	1,788	1,788
Other paid-in capital	39,561	38,808
Retained earnings	45,804	42,579
Accumulated other comprehensive loss	(5,390)	(5,545)
Stockholders' equity before deduction for treasury stock	81,763	77,630
Less treasury stock, at cost: 1,026,214,892 shares in 2019 and 984,543,979 shares in 2018	54,925	50,929
Total Merck & Co., Inc. stockholders’ equity	26,838	26,701
Noncontrolling Interests	87	181
Total equity	26,925	26,882
Liabilities and Equity	$ 83,331	$ 82,637

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEET (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 116	$ 119
Inventories classified in Other assets	1,515	1,417
Accumulated depreciation	$ 17,281	$ 16,324
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)	1,026,214,892	984,543,979

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash Flows from Operating Activities
Net income	$ 7,414	$ 4,415
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,716	3,521
Intangible asset impairment charges	864	0
Charge for acquisition of Peloton Therapeutics, Inc.	982	0
Charge for future payments related to collaboration license options	0	650
Charge for collaboration termination	0	420
Deferred income taxes	(386)	(391)
Share-based compensation	306	261
Other	219	488
Net changes in assets and liabilities	(3,469)	(2,034)
Net Cash Provided by Operating Activities	8,646	7,330
Cash Flows from Investing Activities
Capital expenditures	(2,336)	(1,686)
Purchases of securities and other investments	(2,380)	(6,899)
Proceeds from sales of securities and other investments	7,459	11,243
Acquisition of Antelliq Corporation, net of cash acquired	(3,620)	0
Acquisition of Peloton Therapeutics, Inc., net of cash acquired	(1,040)	0
Other acquisitions, net of cash acquired	(269)	(372)
Other	320	(150)
Net Cash (Used in) Provided by Investing Activities	(1,866)	2,136
Cash Flows from Financing Activities
Net change in short-term borrowings	(3,892)	2,294
Payments on debt	0	(3,007)
Proceeds from issuance of debt	4,958	0
Purchases of treasury stock	(3,730)	(3,158)
Dividends paid to stockholders	(4,290)	(3,895)
Proceeds from exercise of stock options	344	461
Other	(240)	(289)
Net Cash Used in Financing Activities	(6,850)	(7,594)
Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	(26)	(140)
Net (Decrease) Increase in Cash, Cash Equivalents and Restricted Cash	(96)	1,732
Cash, Cash Equivalents and Restricted Cash at Beginning of Year (includes restricted cash of $2 million at January 1, 2019 included in Other Assets)	7,967	6,096
Cash, Cash Equivalents and Restricted Cash at End of Period (includes restricted cash of $2 million at September 30, 2019 included in Other Assets)	$ 7,871	$ 7,828

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Statement of Cash Flows [Abstract]
Restricted cash	$ 2	$ 2

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2019
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, 2019. 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 February 2016, the Financial Accounting Standards Board (FASB) issued new accounting guidance for the accounting and reporting of leases (ASU 2016-02) and subsequently issued several updates to the new guidance (ASC 842 or new guidance). The new guidance requires that lessees recognize a right-of-use asset and a lease liability for each of its leases (other than leases that meet the definition of a short-term lease). Leases are classified as either operating or finance. Operating leases result in straight-line expense in the income statement (similar to previous operating leases), while finance leases result in more expense being recognized in the earlier years of the lease term (similar to previous capital leases). The Company adopted the new standard on January 1, 2019 using a modified retrospective approach. Merck elected the transition method that allows for application of the standard at the adoption date rather than at the beginning of the earliest comparative period presented in the financial statements. The Company also elected available practical expedients. Upon adoption, the Company recognized $1.1 billion of additional assets and related liabilities on its consolidated balance sheet (see Note 8). The adoption of the new guidance did not impact the Company’s consolidated statements of income or cash flows. In April 2018, the FASB issued new guidance on the accounting for costs incurred to implement a cloud computing arrangement that is considered a service arrangement. The new guidance requires the capitalization of such costs, aligning it with the accounting for costs associated with developing or obtaining internal-use software. The Company adopted the new standard in the third quarter of 2019 using prospective application for eligible costs, which were immaterial. Recently Issued Accounting Standards Not Yet Adopted 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, including adoption in any interim period. The new guidance is to be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings in the beginning of the period of adoption. The Company is continuing to assess the impact of adopting the new standard but does not expect the adoption to have a material impact on its consolidated financial statements, subject to the finalization of its assessment. In November 2018, the FASB issued new guidance for collaborative arrangements intended to reduce diversity in practice by clarifying whether certain transactions between collaborative arrangement participants should be accounted for under revenue recognition guidance (ASC 606). The new guidance is effective for interim and annual periods beginning in 2020. Early adoption is permitted, including adoption in any interim period. The new guidance is to be applied on a retrospective basis through a cumulative-effect adjustment directly to retained earnings. The Company does not anticipate the adoption of this standard will have a material effect on its consolidated financial statements.

Acquisitions, Divestitures, Res

Acquisitions, Divestitures, Research Collaborations and License Agreements	9 Months Ended
	Sep. 30, 2019
Business Combinations [Abstract]
Acquisitions, Divestitures, Research Collaborations and License Agreements	Acquisitions, Divestitures, Research Collaborations and License Agreements The Company continues to pursue acquisitions and the 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 July 2019, Merck acquired Peloton Therapeutics, Inc. (Peloton), a clinical-stage biopharmaceutical company focused on the development of novel small molecule therapeutic candidates targeting hypoxia-inducible factor-2α (HIF-2α) for the treatment of patients with cancer and other non-oncology diseases. Peloton’s lead candidate, MK-6482 (formerly PT2977), is a novel oral HIF-2α inhibitor in late-stage development for renal cell carcinoma. Merck made an upfront payment of $1.2 billion in cash; additionally, former Peloton shareholders will be eligible to receive $50 million upon U.S. regulatory approval, $50 million upon first commercial sale in the United States, and up to $1.05 billion of sales-based milestones. The transaction was accounted for as an acquisition of an asset. Merck recorded cash of $157 million , deferred tax liabilities of $64 million , and other net liabilities of $6 million at the acquisition date and Research and development expenses of $982 million in the third quarter and first nine months of 2019 related to the transaction. On April 1, 2019, Merck acquired Antelliq Corporation (Antelliq), a leader in digital animal identification, traceability and monitoring solutions. These solutions help veterinarians, farmers and pet owners gather critical data to improve management, health and well-being of livestock and pets. Merck paid $2.3 billion to acquire all outstanding shares of Antelliq and spent $1.3 billion to repay Antelliq’s debt. The transaction was accounted for as an acquisition of a business. The estimated fair value of assets acquired and liabilities assumed from Antelliq is as follows: ($ in millions) April 1, 2019 Cash and cash equivalents $ 31 Accounts receivable 73 Inventories 95 Property, plant and equipment 62 Identifiable intangible assets (useful lives ranging from 18-24 years) (1) 2,689 Deferred income tax liabilities (563 ) Other assets and liabilities, net (81 ) Total identifiable net assets 2,306 Goodwill (2) 1,345 Consideration transferred $ 3,651 (1) The estimated fair values of identifiable intangible assets relate primarily to trade names and were determined using an income approach. The future net cash flows were discounted to present value utilizing a discount rate of 11.5% . Actual cash flows are likely to be different than those assumed. (2) The goodwill recognized is largely attributable to anticipated synergies expected to arise after the acquisition and was allocated to the Animal Health segment. The goodwill is not deductible for tax purposes. The Company’s results for the first nine months of 2019 include five months of activity for Antelliq. The Company incurred $47 million of transaction costs directly related to the acquisition of Antelliq, consisting largely of advisory fees, which are reflected in Selling, general and administrative expenses in the first nine months of 2019. Also in April 2019, Merck acquired Immune Design, a late-stage immunotherapy company employing next-generation in vivo approaches to enable the body’s immune system to fight disease, for $301 million in cash. The transaction was accounted for as an acquisition of a business. Merck recognized intangible assets for in-process research and development (IPR&D) of $156 million , cash of $83 million and other net assets of $31 million . The excess of the consideration transferred over the fair value of net assets acquired of $31 million was recorded as goodwill that was allocated to the Pharmaceutical segment and is not deductible for tax purposes. The fair values of the identifiable intangible assets related to IPR&D were determined using an income approach. Actual cash flows are likely to be different than those assumed. In the third quarter of 2018, the Company recorded an aggregate charge of $420 million within Cost of sales in conjunction with the termination of a collaboration agreement entered into in 2014 with Samsung Bioepis Co., Ltd. (Samsung) for insulin glargine. The charge reflects a termination payment of $155 million , which represents the reimbursement of all fees previously paid by Samsung to Merck under the agreement, plus interest, as well as the release of Merck’s ongoing obligations under the agreement. The charge also included fixed asset abandonment charges of $137 million , inventory write-offs of $122 million , as well as other related costs of $6 million . The termination of this agreement has no impact on the Company’s other collaboration with Samsung. In June 2018, Merck acquired Viralytics Limited (Viralytics), an Australian publicly traded company focused on oncolytic immunotherapy treatments for a range of cancers, for AUD 502 million ( $378 million ). The transaction provided Merck with full rights to V937 (formerly CVA21), Viralytics’s investigational oncolytic immunotherapy. V937 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. V937 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 V937 combination in melanoma, prostate, lung and bladder cancers. The transaction was accounted for as an acquisition of an asset. Merck recorded net assets of $34 million (primarily cash) at the acquisition date and Research and development expenses of $344 million in the first nine months of 2018 related to the transaction. There are no future contingent payments associated with the acquisition.

Collaborative Arrangements

Collaborative Arrangements	9 Months Ended
	Sep. 30, 2019
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 for multiple cancer types. Lynparza is an oral poly (ADP-ribose) polymerase (PARP) inhibitor currently approved for certain types of ovarian and breast cancer. The companies are jointly developing and commercializing Lynparza, both as monotherapy and in combination trials with other potential medicines. Independently, Merck and AstraZeneca will develop and commercialize Lynparza in combinations with their respective PD-1 and PD-L1 medicines, Keytruda and Imfinzi. The companies will also jointly develop and commercialize AstraZeneca’s selumetinib, an oral, potent, selective inhibitor of MEK, part of the mitogen-activated protein kinase (MAPK) pathway, currently being developed for multiple indications. Under the terms of the agreement, AstraZeneca and Merck will share the development and commercialization costs for Lynparza and selumetinib monotherapy and non-PD-L1/PD-1 combination therapy opportunities. Gross profits from Lynparza and selumetinib product sales generated through monotherapies or combination therapies are shared equally. Merck will fund all development and commercialization costs of Keytruda in combination with Lynparza or selumetinib. AstraZeneca will fund all development and commercialization costs of Imfinzi in combination with Lynparza or selumetinib. AstraZeneca is the principal on Lynparza sales transactions. Merck records its share of Lynparza product sales, net of cost of sales and commercialization costs, as alliance revenue within the Pharmaceutical segment and its share of development costs associated with the collaboration as part of Research and development costs. 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 in 2017 and will make payments of up to $750 million over a multi-year period for certain license options (of which $250 million was paid in December 2017, $400 million was paid in December 2018 and $100 million is expected to be paid in December 2019). The Company recorded an aggregate charge of $2.35 billion in Research and development expenses in 2017 related to the upfront payment and license option payments. In addition, the agreement provides for additional contingent payments from Merck to AstraZeneca related to the successful achievement of sales-based and regulatory milestones. In the second quarter of 2019, Merck determined it was probable that annual sales of Lynparza in the future would trigger a $300 million sales-based milestone payment from Merck to AstraZeneca. Accordingly, in the second quarter of 2019, Merck recorded a $300 million liability and a corresponding increase to the intangible asset related to Lynparza and also recognized $52 million of cumulative amortization expense within Cost of sales . Prior to 2019, Merck accrued sales-based milestone payments aggregating $700 million related to Lynparza. Of these amounts, $450 million has been paid to AstraZeneca. Potential future sales-based milestone payments of $3.1 billion have not yet been accrued as they are not deemed by the Company to be probable at this time. In April 2019, Lynparza received regulatory approval in the European Union (EU) as a monotherapy for the treatment of certain adult patients with advanced breast cancer, triggering a $30 million capitalized milestone payment from Merck to AstraZeneca. In June 2019, Lynparza received regulatory approval in the EU as a monotherapy for the maintenance treatment of certain adult patients with BRCA -mutated advanced ovarian cancer, triggering a $30 million capitalized milestone payment from Merck to AstraZeneca. In 2018, Lynparza received regulatory approvals triggering capitalized milestone payments of $140 million in the aggregate from Merck to AstraZeneca. Potential future regulatory milestone payments of $1.7 billion remain under the agreement. The asset balance related to Lynparza (which includes capitalized sales-based and regulatory milestone payments) was $983 million at September 30, 2019 and is included in Other Assets on the Consolidated Balance Sheet. The amount is being amortized over its estimated useful life through 2028 as supported by projected future cash flows, subject to impairment testing. Summarized financial information related to this collaboration is as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Alliance revenue $ 123 $ 49 $ 313 $ 125 Cost of sales (1) 28 12 120 48 Selling, general and administrative 36 12 96 28 Research and development 44 47 122 118 ($ in millions) September 30, 2019 December 31, 2018 Receivables from AstraZeneca included in Other current assets $ 119 $ 52 Payables to AstraZeneca included in Accrued and other current liabilities (2) 578 405 Payables to AstraZeneca included in Other Noncurrent Liabilities (3) 300 250 (1) Represents amortization of capitalized milestone payments. (2) Includes accrued milestone and license option payments. (3) Includes accrued milestone payments. Eisai In March 2018, Merck and Eisai announced a strategic collaboration for the worldwide co-development and co-commercialization of Lenvima, an orally available tyrosine kinase inhibitor discovered by Eisai. Under the agreement, Merck and Eisai will develop and commercialize Lenvima jointly, both as monotherapy and in combination with Merck’s anti-PD-1 therapy, Keytruda . Eisai records Lenvima product sales globally (Eisai is the principal on Lenvima sales transactions), and Merck and Eisai share gross profits equally. Merck records its share of Lenvima product sales, net of cost of sales and commercialization costs, as alliance revenue. Expenses incurred during co-development, including for studies evaluating Lenvima as monotherapy, are shared equally by the two companies and reflected in Research and development costs. Under the agreement, Merck made an upfront payment to Eisai of $750 million and will make payments of up to $650 million for certain option rights through 2021 (of which $325 million was paid in March 2019, $200 million is expected to be paid in March 2020 and $125 million is expected to be paid in March 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 payment and future option payments. In addition, the agreement provides for Eisai to receive up to $385 million associated with the achievement of certain regulatory milestones and up to $3.97 billion for the achievement of milestones associated with sales of Lenvima. In the first quarter of 2019, Merck determined it was probable that annual sales of Lenvima in the future would trigger $282 million of sales-based milestone payments from Merck to Eisai. Accordingly, in the first quarter of 2019, Merck recorded $282 million of liabilities and corresponding increases to the intangible asset related to Lenvima and also recognized $35 million of cumulative amortization expense within Cost of sales . Merck previously accrued sales-based milestone payments aggregating $268 million related to Lenvima in 2018. Of these amounts, $50 million has been paid to Eisai. Potential future sales-based milestone payments of $3.42 billion have not yet been accrued as they are not deemed by the Company to be probable at this time. In 2018, Lenvima received regulatory approvals triggering capitalized milestone payments of $250 million in the aggregate from Merck to Eisai. Potential future regulatory milestone payments of $135 million remain under the agreement. The asset balance related to Lenvima (which includes capitalized sales-based and regulatory milestone payments) was $664 million at September 30, 2019 and is included in Other Assets on the Consolidated Balance Sheet. The amount is being amortized over its estimated useful life through 2026 as supported by projected future cash flows, subject to impairment testing. Summarized financial information related to this collaboration is as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Alliance revenue $ 109 $ 43 $ 280 $ 78 Cost of sales (1) 23 8 97 9 Selling, general and administrative 21 5 59 7 Research and development (2) 37 36 146 1,473 ($ in millions) September 30, 2019 December 31, 2018 Receivables from Eisai included in Other current assets $ 109 $ 71 Payables to Eisai included in Accrued and other current liabilities (3) 692 375 Payables to Eisai included in Other Noncurrent Liabilities (3) 125 543 (1) Represents amortization of capitalized milestone payments. (2) Amount for the first nine months of 2018 includes the upfront payment and future option payments. (3) Includes accrued milestone and option payments. Bayer AG In 2014, the Company entered into a worldwide clinical development collaboration with Bayer AG (Bayer) to market and develop soluble guanylate cyclase (sGC) modulators including Bayer’s Adempas, which is approved to treat pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. The two companies have implemented a joint development and commercialization strategy. The collaboration also includes clinical development of Bayer’s vericiguat, which is in Phase 3 trials for worsening heart failure, as well as opt-in rights for other early-stage sGC compounds in development by Bayer. Merck in turn made available its early-stage sGC compounds under similar terms. Under the agreement, Bayer leads commercialization of Adempas in the Americas, while Merck leads commercialization in the rest of the world. For vericiguat and other potential opt-in products, Bayer will lead commercialization in the rest of world and Merck will lead in the Americas. For all products and candidates included in the agreement, both companies will share in development costs and profits on sales and will have the right to co-promote in territories where they are not the lead. Revenue from Adempas includes sales in Merck’s marketing territories, as well as Merck’s share of profits from the sale of Adempas in Bayer’s marketing territories. In the first quarter of 2018, Merck made a $350 million sales-based milestone payment to Bayer, which was accrued for in 2016 when Merck deemed the payment to be probable. In the second quarter of 2018, Merck determined it was probable that annual worldwide sales of Adempas in the future would trigger a $375 million sales-based milestone payment from Merck to Bayer; accordingly, Merck recorded a $375 million liability and a corresponding increase to the intangible asset related to Adempas and also recognized $106 million of cumulative amortization expense within Cost of sales . There is an additional $400 million potential future sales-based milestone payment that has not yet been accrued as it is not deemed by the Company to be probable at this time. The intangible asset balance related to Adempas (which includes the acquired intangible asset balance, as well as capitalized sales-based milestone payments) was $893 million at September 30, 2019 and is included in Other Intangibles, Net on the Consolidated Balance Sheet. The amount is being amortized over its estimated useful life through 2027 as supported by projected future cash flows, subject to impairment testing. Summarized financial information related to this collaboration is as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Net product sales recorded by Merck $ 57 $ 47 $ 158 $ 138 Merck’s profit share from sales in Bayer’s marketing territories 50 47 144 100 Total sales 107 94 302 238 Cost of sales (1) 28 29 86 188 Selling, general and administrative 12 11 31 26 Research and development 31 34 94 90 ($ in millions) September 30, 2019 December 31, 2018 Receivables from Bayer included in Other current assets $ 44 $ 32 Payables to Bayer included in Other Noncurrent Liabilities (2) 375 375 (1) Includes amortization of intangible assets. (2) Represents accrued milestone payment.

Restructuring

Restructuring	9 Months Ended
	Sep. 30, 2019
Restructuring and Related Activities [Abstract]
Restructuring	Restructuring Merck recently approved a new global restructuring program (2019 Restructuring Program) as part of a worldwide initiative focused primarily on further optimizing the Company’s manufacturing and supply network, as well as reducing its global real estate footprint. This program is a continuation of the Company’s plant rationalization and builds on prior restructuring programs. The Company will continue to evaluate its global footprint and overall operating model, which could result in the identification of additional actions over time. The actions contemplated under the 2019 Restructuring Program are expected to be substantially completed by the end of 2023, with the cumulative pretax costs to be incurred by the Company to implement the program estimated to be approximately $800 million to $1.2 billion . The Company estimates that approximately 60% of the cumulative pretax costs will result in cash outlays, primarily related to employee separation expense and facility shut-down costs. Approximately 40% of the cumulative pretax costs will be non-cash, relating primarily to the accelerated depreciation of facilities to be closed or divested. The Company expects to record charges of approximately $750 million in 2019 related to the program. Actions under previous global restructuring programs have been substantially completed. The Company recorded total pretax costs of $296 million and $169 million in the third quarter of 2019 and 2018 , respectively, and $642 million and $508 million for the first nine months of 2019 and 2018, respectively, related to restructuring program activities. For segment reporting, restructuring charges are unallocated expenses. The following tables summarize the charges related to restructuring program activities by type of cost: Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 ($ in millions) Separation Costs Accelerated Depreciation Other Total Separation Costs Accelerated Depreciation Other Total Cost of sales $ — $ 41 $ 21 $ 62 $ — $ 139 $ 22 $ 161 Selling, general and administrative — 1 — 1 — 33 — 33 Research and development — (1 ) 2 1 — 1 3 4 Restructuring costs 205 — 27 232 358 — 86 444 $ 205 $ 41 $ 50 $ 296 $ 358 $ 173 $ 111 $ 642 Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 ($ in millions) Separation Costs Accelerated Depreciation Other Total Separation Costs Accelerated Depreciation Other Total Cost of sales $ — $ 1 $ 1 $ 2 $ — $ 1 $ 10 $ 11 Selling, general and administrative — — — — — 1 1 2 Research and development — (9 ) 5 (4 ) — (12 ) 13 1 Restructuring costs 137 — 34 171 392 — 102 494 $ 137 $ (8 ) $ 40 $ 169 $ 392 $ (10 ) $ 126 $ 508 Separation costs are associated with actual headcount reductions, as well as those headcount reductions which were probable and could be reasonably estimated. Accelerated depreciation costs primarily relate to manufacturing, research and administrative facilities and equipment to be sold or closed as part of the programs. Accelerated depreciation costs represent the difference between the depreciation expense to be recognized over the revised useful life of the asset, based upon the anticipated date the site will be closed or divested or the equipment disposed of, and depreciation expense as determined utilizing the useful life prior to the restructuring actions. All the sites have and will continue to operate up through the respective closure dates and, since future undiscounted cash flows are 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 2019 and 2018 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 12) and share-based compensation. The following table summarizes the charges and spending relating to restructuring program activities for the nine months ended September 30, 2019 : ($ in millions) Separation Costs Accelerated Depreciation Other Total Restructuring reserves January 1, 2019 $ 443 $ — $ 91 $ 534 Expense 358 173 111 642 (Payments) receipts, net (198 ) — (158 ) (356 ) Non-cash activity — (173 ) 20 (153 ) Restructuring reserves September 30, 2019 (1) $ 603 $ — $ 64 $ 667 (1)

Financial Instruments

Financial Instruments	9 Months Ended
	Sep. 30, 2019
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, Japanese yen and Chinese renminbi. 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 . The Company recognizes 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 effects of the Company’s net investment hedges on OCI and the Consolidated Statement of Income are shown below: Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income (1) Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing Three Months Ended September 30, Nine Months Ended September 30, Three Months Ended September 30, Nine Months Ended September 30, ($ in millions) 2019 2018 2019 2018 2019 2018 2019 2018 Net Investment Hedging Relationships Foreign exchange contracts $ 1 $ (10 ) $ 8 $ (24 ) $ (8 ) $ (4 ) $ (23 ) $ (7 ) Euro-denominated notes (150 ) 38 (152 ) (54 ) — — — — (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 September 30, 2019 , the Company was a party to 19 pay-floating, receive-fixed interest rate swap contracts designated as fair value hedges of fixed-rate notes in which the notional amounts match the amount of the hedged fixed-rate notes as detailed in the table below. September 30, 2019 ($ in millions) Par Value of Debt Number of Interest Rate Swaps Held Total Swap Notional Amount 1.85% notes due 2020 $ 1,250 5 $ 1,250 3.875% notes due 2021 1,150 5 1,150 2.40% notes due 2022 1,000 4 1,000 2.35% notes due 2022 1,250 5 1,250 The interest rate swap contracts are designated hedges of the fair value changes in the notes attributable to changes in the benchmark London Interbank Offered Rate (LIBOR) swap rate. The fair value changes in the notes attributable to changes in the LIBOR swap rate are recorded in interest expense along with the offsetting fair value changes in the swap contracts. The cash flows from these contracts are reported as operating activities in the 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 Liabilities Cumulative Amount of Fair Value Hedging Adjustment Increase (Decrease) Included in the Carrying Amount ($ in millions) September 30, 2019 December 31, 2018 September 30, 2019 December 31, 2018 Balance Sheet Line Item in which Hedged Item is Included Loans payable and current portion of long-term debt $ 1,247 $ — $ (3 ) $ — Long-Term Debt 3,416 4,560 22 (82 ) 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: September 30, 2019 December 31, 2018 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 $ 22 $ — $ 3,400 $ — $ — $ — Interest rate swap contracts Accrued and other current liabilities — 3 1,250 — — — Interest rate swap contracts Other Noncurrent Liabilities — — — — 81 4,650 Foreign exchange contracts Other current assets 252 — 7,144 263 — 6,222 Foreign exchange contracts Other Assets 56 — 2,073 75 — 2,655 Foreign exchange contracts Accrued and other current liabilities — 6 775 — 7 774 Foreign exchange contracts Other Noncurrent Liabilities — 1 9 — 1 89 $ 330 $ 10 $ 14,651 $ 338 $ 89 $ 14,390 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts Other current assets $ 153 $ — $ 6,802 $ 116 $ — $ 5,430 Foreign exchange contracts Accrued and other current liabilities — 100 6,906 — 71 9,922 $ 153 $ 100 $ 13,708 $ 116 $ 71 $ 15,352 $ 483 $ 110 $ 28,359 $ 454 $ 160 $ 29,742 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: September 30, 2019 December 31, 2018 ($ in millions) Asset Liability Asset Liability Gross amounts recognized in the condensed consolidated balance sheet $ 483 $ 110 $ 454 $ 160 Gross amounts subject to offset in master netting arrangements not offset in the condensed consolidated balance sheet (73 ) (73 ) (121 ) (121 ) Cash collateral received (133 ) — (107 ) — Net amounts $ 277 $ 37 $ 226 $ 39 The table below provides information regarding the location and amount of pretax (gains) losses of derivatives designated in fair value or cash flow hedging relationships: Sales Other (income) expense, net (1) Other comprehensive income (loss) Sales Other (income) expense, net (1) Other comprehensive income (loss) Three Months Ended September 30, Three Months Ended September 30, Three Months Ended September 30, Nine Months Ended September 30, Nine Months Ended September 30, Nine Months Ended September 30, ($ in millions) 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 Financial Statement Line Items in which Effects of Fair Value or Cash Flow Hedges are Recorded $ 12,397 $ 10,794 $ 35 $ (172 ) $ (28 ) $ (29 ) $ 34,972 $ 31,296 $ 362 $ (512 ) $ 155 $ 33 (Gain) loss on fair value hedging relationships Interest rate swap contracts Hedged items — — 13 (9 ) — — — — 101 (86 ) — — Derivatives designated as hedging instruments — — (6 ) 15 — — — — (74 ) 100 — — Impact of cash flow hedging relationships Foreign exchange contracts Amount of income (loss) recognized in OCI on derivatives — — — — 186 29 — — — — 183 113 Increase (decrease) in Sales as a result of AOCI reclassifications 70 (6 ) — — (70 ) 6 189 (172 ) — — (189 ) 172 Interest rate contracts Amount of gain recognized in Other (income) expense, net on derivatives — — (1 ) (1 ) — — — — (3 ) (3 ) — — Amount of loss recognized in OCI on derivatives — — — — (1 ) (1 ) — — — — (6 ) (3 ) (1) Interest expense is a component of Other (income) expense, net. The table below provides information regarding the income statement effects of derivatives not designated as hedging instruments: Amount of Derivative Pretax (Gain) Loss Recognized in Income Three Months Ended September 30, Nine Months Ended September 30, ($ in millions) Income Statement Caption 2019 2018 2019 2018 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts (1) Other (income) expense, net $ (8 ) $ (57 ) $ 112 $ (224 ) Foreign exchange contracts (2) Sales (11 ) — (7 ) (5 ) (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 September 30, 2019 , the Company estimates $174 million of pretax net unrealized gains on derivatives maturing within the next 12 months that hedge foreign currency denominated sales over that same period will be reclassified from AOCI to Sales . The amount ultimately reclassified to Sales may differ as foreign exchange rates change. Realized gains and losses are ultimately determined by actual exchange rates at maturity. Investments in Debt and Equity Securities Information on investments in debt and equity securities is as follows: September 30, 2019 December 31, 2018 Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized Fair Value ($ in millions) Gains Losses Gains Losses Corporate notes and bonds $ 1,260 $ 24 $ — $ 1,284 $ 4,985 $ 3 $ (68 ) $ 4,920 Asset-backed securities 434 3 — 437 1,285 1 (11 ) 1,275 U.S. government and agency securities 358 4 — 362 895 2 (5 ) 892 Foreign government bonds 32 — — 32 167 — (1 ) 166 Mortgage-backed securities — — — — 8 — — 8 Total debt securities $ 2,084 $ 31 $ — $ 2,115 $ 7,340 $ 6 $ (85 ) $ 7,261 Publicly traded equity securities (1) 691 456 Total debt and publicly traded equity securities $ 2,806 $ 7,717 (1) Unrealized net losses (gains) recognized in Other (income) expense, net on equity securities still held at September 30, 2019 were $25 million and $(10) million , for the third quarter of 2019 and 2018 , respectively, and were $(41) million and $(60) million for the first nine months of 2019 and 2018 , respectively. At September 30, 2019 , the Company also had $393 million of equity investments without readily determinable fair values included in Other Assets . During the first nine months of 2019 , the Company recognized unrealized gains of $4 million on certain of these equity investments recorded in Other (income) expense, net based on favorable observable price changes from transactions involving similar investments of the same investee. In addition, during the first nine months of 2019, the Company recognized unrealized losses of $12 million in Other (income) expense, net related to certain of these investments based on unfavorable observable price changes. Since January 1, 2018, cumulative unrealized gains and cumulative unrealized losses based on observable prices changes for investments in equity investments without readily determinable fair values were $172 million and $21 million , respectively. Available-for-sale debt securities included in Short-term investments totaled $129 million at September 30, 2019 . Of the remaining debt securities, $1.8 billion mature within five years. At September 30, 2019 and December 31, 2018 , 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) September 30, 2019 December 31, 2018 Assets Investments Corporate notes and bonds $ — $ 1,284 $ — $ 1,284 $ — $ 4,835 $ — $ 4,835 Asset-backed securities (1) — 437 — 437 — 1,253 — 1,253 U.S. government and agency securities — 301 — 301 — 731 — 731 Foreign government bonds — 32 — 32 — 166 — 166 Publicly traded equity securities 206 — — 206 147 — — 147 206 2,054 — 2,260 147 6,985 — 7,132 Other assets (2) U.S. government and agency securities 61 — — 61 55 106 — 161 Corporate notes and bonds — — — — — 85 — 85 Mortgage-backed securities — — — — — 8 — 8 Asset-backed securities (1) — — — — — 22 — 22 Publicly traded equity securities 485 — — 485 309 — — 309 546 — — 546 364 221 — 585 Derivative assets (3) Forward exchange contracts — 259 — 259 — 241 — 241 Purchased currency options — 202 — 202 — 213 — 213 Interest rate swaps — 22 — 22 — — — — — 483 — 483 — 454 — 454 Total assets $ 752 $ 2,537 $ — $ 3,289 $ 511 $ 7,660 $ — $ 8,171 Liabilities Other liabilities Contingent consideration $ — $ — $ 755 $ 755 $ — $ — $ 788 $ 788 Derivative liabilities (3) Forward exchange contracts — 105 — 105 — 74 — 74 Interest rate swaps — 3 — 3 — 81 — 81 Written currency options — 2 — 2 — 5 — 5 — 110 — 110 — 160 — 160 Total liabilities $ — $ 110 $ 755 $ 865 $ — $ 160 $ 788 $ 948 (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 nine months of 2019 . As of September 30, 2019 , Cash and cash equivalents of $7.9 billion included $7.1 billion of cash equivalents (which would be considered Level 2 in the fair value hierarchy). Contingent Consideration Summarized information about the changes in liabilities for contingent consideration is as follows: Nine Months Ended September 30, ($ in millions) 2019 2018 Fair value January 1 $ 788 $ 935 Changes in estimated fair value (1) 52 144 Additions — 8 Payments (85 ) (235 ) Fair value September 30 (2) $ 755 $ 852 (1) Recorded in Cost of sales, Research and development expenses, and Other (income) expense, net . Includes cumulative translation adjustments. (2) Balance at September 30, 2019 includes $112 million recorded as a current liability for amounts expected to be paid within the next 12 months. The payments of contingent consideration in both periods include payments related to liabilities recorded in connection with the 2016 termination of the Sanofi-Pasteur MSD joint venture. The payments of contingent consideration in the first nine months of 2018 also include $175 million related to the achievement of a clinical development milestone for MK-7264 (gefapixant), a program obtained in connection with the acquisition of Afferent Pharmaceuticals. 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 September 30, 2019 , was $28.7 billion compared with a carrying value of $26.1 billion and at December 31, 2018 , was $25.6 billion compared with a carrying value of $25.1 billion . Fair value was estimated using recent observable market prices and would be considered Level 2 in the fair value hierarchy. Concentrations of Credit Risk On an ongoing basis, the Company monitors concentrations of credit risk associated with corporate and government issuers of securities and financial institutions with which it conducts business. Credit exposure limits are established to limit a concentration with any single issuer or institution. Cash and investments are placed in instruments that meet high credit quality standards as specified in the Company’s investment policy guidelines. The majority of the Company’s accounts receivable arise from product sales in the United States and Europe and are primarily due from drug wholesalers and retailers, hospitals, government agencies, managed health care providers and pharmacy benefit managers. The Company monitors the financial performance and creditworthiness of its customers so that it can properly assess and respond to changes in their credit profile. The Company also continues to monitor global economic conditions, including the volatility associated with international sovereign economies, and associated impacts on the financial markets and its business. The Company 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. Cash received by the Company from various counterparties was $133 million and $107 million at September 30, 2019 and December 31, 2018 , respectively. The obligation to return such collateral is recorded in Accrued and other current liabilities . No cash collateral was advanced by the Company to counterparties as of September 30, 2019 or December 31, 2018 .

Inventories

Inventories	9 Months Ended
	Sep. 30, 2019
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories consisted of: ($ in millions) September 30, 2019 December 31, 2018 Finished goods $ 1,698 $ 1,658 Raw materials and work in process 5,526 5,004 Supplies 213 194 Total (approximates current cost) 7,437 6,856 (Decrease) increase to LIFO costs (67 ) 1 $ 7,370 $ 6,857 Recognized as: Inventories $ 5,855 $ 5,440 Other assets 1,515 1,417 Amounts recognized as Other Assets are comprised almost entirely of raw materials and work in process inventories. At September 30, 2019 and December 31, 2018 , these amounts included $1.4 billion of inventories not expected to be sold within one year. In addition, these amounts included $138 million and $7 million at September 30, 2019 and December 31, 2018 , respectively, of inventories produced in preparation for product launches.

Other Intangibles

Other Intangibles	9 Months Ended
	Sep. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Other Intangibles	Other Intangibles In connection with business acquisitions, the Company measures the fair value of marketed products and research and development pipeline programs and capitalizes these amounts. See Note 2 for information on intangible assets acquired as a result of business acquisitions in the first nine months of 2019 and 2018. During the third quarter and first nine months of 2019, the Company recorded $612 million and $693 million , respectively, of intangible asset impairment charges related to marketed products within Cost of sales . During the third quarter of 2019, the Company recorded an impairment charge of $612 million related to Sivextro (tedizolid phosphate), a product for the treatment of acute bacterial skin and skin structure infections caused by designated susceptible Gram-positive organisms. In the third quarter of 2019, as part of a reorganization and reprioritization of its internal sales force, the Company made the decision to cease promotion of Sivextro in the U.S. market by the end of 2019. This decision resulted in reduced ca sh flow projections for Sivextro , which indicated that the Sivextro intangible asset value was not fully recoverable on an undiscounted cash flows basis. The Company utilized market participant assumptions to determine its best estimate of the fair value of the intangible asset related to Sivextro that, when compared with its related carrying value, resulted in the impairment charge noted above. The remaining intangible asset value for Sivextro was $175 million

Loans Payable, Long-Term Debt a

Loans Payable, Long-Term Debt and Leases	9 Months Ended
	Sep. 30, 2019
Loans Payable, Long-Term Debt and Leases [Abstract]
Loans Payable, Long-Term Debt and Leases	Loans Payable, Long-Term Debt and Leases Long-Term Debt In March 2019, the Company issued $5.0 billion principal amount of senior unsecured notes consisting of $750 million of 2.90% notes due 2024, $1.75 billion of 3.40% notes due 2029, $1.0 billion of 3.90% notes due 2039, and $1.5 billion of 4.00% notes due 2049. The Company used the net proceeds from the offering of $5.0 billion for general corporate purposes, including the repayment of outstanding commercial paper borrowings. Leases As discussed in Note 1, on January 1, 2019, Merck adopted new guidance for the accounting and reporting of leases. The Company has operating leases primarily for manufacturing facilities, research and development facilities, corporate offices, employee housing, vehicles and certain equipment. As permitted under the transition guidance in ASC 842, the Company elected a package of practical expedients which, among other provisions, allowed the Company to carry forward historical lease classifications. The Company determines if an arrangement is a lease at inception. When evaluating contracts for embedded leases, the Company exercises judgment to determine if there is an explicit or implicit identified asset in the contract and if Merck controls the use of that asset. Embedded leases, primarily associated with contract manufacturing organizations, are immaterial. Under ASC 842 transition guidance, Merck elected the hindsight practical expedient to determine the lease term for existing leases, which permits companies to consider available information prior to the effective date of the new guidance as to the actual or likely exercise of options to extend or terminate the lease. The lease term includes options to extend or terminate the lease when it is reasonably certain that Merck will exercise that option. Real estate leases for facilities have an average remaining lease term of eight years , which include options to extend the leases for up to four years where applicable. Vehicle leases are generally in effect for four years . The Company has made an accounting policy election not to record short-term leases (leases with an initial term of 12 months or less) on the balance sheet; however, Merck currently has no short-term leases. Lease expense for operating lease payments is recognized on a straight-line basis over the term of the lease. Operating lease assets and liabilities are recognized based on the present value of lease payments over the lease term. Since most of the Company’s leases do not have a readily determinable implicit discount rate, the Company uses its incremental borrowing rate to calculate the present value of lease payments. As a practical expedient, the Company has made an accounting policy election not to separate lease components (e.g. payments for rent, real estate taxes and insurance costs) from non-lease components (e.g. common-area maintenance costs) in the event that the agreement contains both. Merck includes both the lease and non-lease components for purposes of calculating the right-of-use asset and related lease liability (if the non-lease components are fixed). For vehicle leases and employee housing, the Company applies a portfolio approach to effectively account for the operating lease assets and liabilities. Certain of the Company’s lease agreements contain variable lease payments that are adjusted periodically for inflation or for actual operating expense true-ups compared with estimated amounts; however, these amounts are immaterial. Sublease income and activity related to sale and leaseback transactions are immaterial. Merck’s lease agreements do not contain any material residual value guarantees or material restrictive covenants. Operating lease cost was $79 million and $244 million for the third quarter and first nine months of 2019, respectively. Cash paid for amounts included in the measurement of operating lease liabilities was $71 million and $209 million for the third quarter and first nine months of 2019, respectively. Supplemental balance sheet information related to operating leases is as follows: ($ in millions) September 30, 2019 Assets Other Assets (1) $ 1,085 Liabilities Accrued and other current liabilities $ 241 Other Noncurrent Liabilities 779 $ 1,020 Weighted-average remaining lease term (years) 7.5 Weighted-average discount rate 3.3 % (1) Includes prepaid leases that have no related lease liability. Maturities of operating leases liabilities are as follows: ($ in millions) September 30, 2019 2019 (excluding the nine months ended September 30, 2019) $ 71 2020 235 2021 189 2022 155 2023 127 Thereafter 374 Total lease payments 1,151 Less: imputed interest (131 ) $ 1,020 As of September 30, 2019 , the Company had entered into additional real estate operating leases that had not yet commenced. The obligations associated with these leases totaled $444 million , of which $221 million relates to a lease that will commence in April 2020 and has a lease term of 10 years . As of December 31, 2018, prior to the adoption of ASC 842, the minimum aggregate rental commitments under noncancellable leases were as follows: 2019, $188 million ; 2020, $198 million ; 2021, $150 million ; 2022, $134 million ; 2023, $84 million and thereafter, $243 million

Contingencies

Contingencies	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 , approximately 3,900 cases have been filed and either are pending or conditionally dismissed (as noted below) against Merck in either federal or state court. Plaintiffs in the vast majority of these cases generally allege that they sustained femur fractures and/or other bone injuries (Femur Fractures) in association with the use of Fosamax . All federal cases involving allegations of Femur Fracture have been or will be transferred to a multidistrict litigation in the District of New Jersey (Femur Fracture MDL). In the only bellwether case tried to date in the Femur Fracture MDL, Glynn v. Merck , the jury returned a verdict in Merck’s favor. In addition, in June 2013, the Femur Fracture MDL court granted Merck’s motion for judgment as a matter of law in the Glynn case and held that the plaintiff’s failure to warn claim was preempted by federal law. In August 2013, the Femur Fracture MDL court entered an order requiring plaintiffs in the Femur Fracture MDL to show cause why those cases asserting claims for a femur fracture injury that took place prior to September 14, 2010, should not be dismissed based on the court’s preemption decision in the Glynn case. Pursuant to the show cause order, in March 2014, the Femur Fracture MDL court dismissed with prejudice approximately 650 cases on preemption grounds. Plaintiffs in approximately 515 of those cases appealed that decision to the U.S. Court of Appeals for the Third Circuit (Third Circuit). In March 2017, the Third Circuit issued a decision reversing the Femur Fracture MDL court’s preemption ruling and remanding the appealed cases back to the Femur Fracture MDL court. Merck filed a petition for a writ of certiorari to the U.S. Supreme Court in August 2017 seeking review of the Third Circuit’s decision. In December 2017, the Supreme Court invited the Solicitor General to file a brief in the case expressing the views of the United States, and in May 2018, the Solicitor General submitted a brief stating that the Third Circuit’s decision was wrongly decided and recommended that the Supreme Court grant Merck’s cert petition. The Supreme Court granted Merck’s petition in June 2018, and an oral argument before the Supreme Court was held on January 7, 2019. On May 20, 2019, the Supreme Court issued its opinion and decided that the Third Circuit had incorrectly concluded that the issue of preemption should be resolved by a jury, and accordingly vacated the judgment of the Third Circuit and remanded the proceedings back to the Third Circuit to address the issue in a manner consistent with the Supreme Court’s opinion. The Third Circuit requested, by August 6, 2019, ten-page letters from each side addressing two specific issues central to the appeal. Both sides submitted their letter briefs and await a decision from the Third Circuit. Accordingly, as of September 30, 2019 , 11 cases were actively pending in the Femur Fracture MDL, and approximately 1,060 cases have either been dismissed without prejudice or administratively closed pending final resolution by the Third Circuit of the appeal of the Femur Fracture MDL court’s preemption order. As of September 30, 2019 , approximately 2,520 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 cases to be reviewed through fact discovery. Merck has continued to select additional cases to be reviewed through fact discovery from 2016 to the present. As of September 30, 2019 , approximately 275 cases alleging Femur Fractures have been filed and are pending in California state court. All of the Femur Fracture cases filed in California state court have been coordinated before a single judge in Orange County, California. Additionally, there are four Femur Fracture cases pending in other state courts. Discovery is presently stayed in the Femur Fracture MDL and in the state court cases in California. Merck 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 September 30, 2019 , Merck is aware of approximately 1,370 product users alleging that Januvia and/or Janumet caused the development of pancreatic cancer and other injuries. Most claims have been filed in multidistrict litigation before the U.S. District Court for the Southern District of California (MDL). Outside of the MDL, the majority of claims have been filed in coordinated proceedings before the Superior Court of California, County of Los Angeles (California State Court). In November 2015, the MDL and California State Court-in separate opinions-granted summary judgment to defendants on grounds of federal preemption. Plaintiffs appealed in both forums. In November 2017, the U.S. Court of Appeals for the Ninth Circuit vacated the judgment and remanded for further discovery, which is ongoing. In November 2018, the California state appellate court reversed and remanded on similar grounds. In March 2019, the parties in the MDL and the California coordinated proceeding agreed to coordinate and adopt a schedule for completing discovery on general causation and preemption issues and for renewing summary judgment and Daubert motions. Under the stipulated case management schedule, the filing deadline for Daubert and summary judgment motions will take place in May 2020. As of September 30, 2019 , six product users have claims pending against Merck in state courts other than California, including Illinois. In June 2017, the Illinois trial court denied Merck’s motion for summary judgment based on federal preemption. Merck appealed, and the Illinois appellate court affirmed in December 2018. Merck filed a petition for leave to appeal to the Illinois Supreme Court in February 2019. In April 2019, the Illinois Supreme Court stayed consideration of the pending petition to appeal until the United States Supreme Court issued its opinion in Merck Sharp & Dohme Corp. v. Albrecht (relating to the Fosamax matter discussed above). Merck filed the opinion in Albrecht with the Illinois Supreme Court in June 2019. The petition for leave to appeal was decided on September 25, 2019, in which the Illinois Supreme Court directed the intermediate appellate court to reconsider its earlier ruling. In addition to the claims noted above, the Company has agreed to toll the statute of limitations for approximately 50 additional claims. The Company intends to continue defending against these lawsuits. Governmental Proceedings As previously disclosed, in July 2017, Merck received a subpoena from the California Department of Insurance (DOI) pursuant to an investigation of whether, prior to Merck’s acquisition of the company, Cubist Pharmaceuticals unlawfully induced the presentation of false claims for Cubicin to private insurers under the California Insurance Code False Claims Act. By letter dated August 12, 2019, the DOI advised Merck that it was withdrawing the subpoena and closing its investigation. As previously disclosed, the Company’s subsidiaries in China have, in the past, received and may continue to receive inquiries regarding their operations from various Chinese governmental agencies. Some of these inquiries may be related to matters involving other multinational pharmaceutical companies, as well as Chinese entities doing business with such companies. The Company’s policy is to cooperate with these authorities and to provide responses as appropriate. As previously disclosed, from time to time, the Company receives inquiries and is the subject of preliminary investigation activities from competition and other governmental authorities in markets outside the United States. These authorities may include regulators, administrative authorities, and law enforcement and other similar officials, and these preliminary investigation activities may include site visits, formal or informal requests or demands for documents or materials, inquiries or interviews and similar matters. Certain of these preliminary inquiries or activities may lead to the commencement of formal proceedings. Should those proceedings be determined adversely to the Company, monetary fines and/or remedial undertakings may be required. Commercial and Other Litigation Zetia Antitrust Litigation As previously disclosed, Merck, MSD, Schering Corporation and MSP Singapore Company LLC (collectively, the Merck Defendants) are defendants in putative class action and opt-out lawsuits filed in 2018 on behalf of direct and indirect purchasers of Zetia alleging violations of federal and state antitrust laws, as well as other state statutory and common law causes of action. The cases have been consolidated for pretrial purposes in a federal multidistrict litigation before Judge Rebecca Beach Smith in the Eastern District of Virginia. In December 2018, the court denied the Merck Defendants’ motions to dismiss or stay the direct purchaser putative class actions pending bilateral arbitration. On August 9, 2019, the district court adopted in full the report and recommendation of the magistrate judge, thereby granting in part and denying in part Merck Defendants’ motions to dismiss on non-arbitration issues. In addition, on June 27, 2019, the representatives of the putative direct purchaser class filed an amended complaint, and on August 1, 2019, retailer opt-out plaintiffs filed an amended complaint. The Merck Defendants moved to dismiss the new allegations in both complaints. On October 15, 2019, the magistrate judge issued a report and recommendation recommending that the district judge grant the motions in their entirety. Trial is currently scheduled to begin on October 14, 2020. Rotavirus Vaccines Antitrust Litigation As previously disclosed, MSD is a defendant in putative class action lawsuits filed in 2018 on behalf of direct purchasers of RotaTeq , alleging violations of federal antitrust laws. The cases were consolidated in the Eastern District of Pennsylvania. On January 23, 2019, the court denied MSD’s motions to compel arbitration and to dismiss the consolidated complaint. On February 19, 2019, MSD appealed the court’s order on arbitration to the Third Circuit. On October 28, 2019, the Third Circuit vacated the district court’s order and remanded for limited discovery on the issue of arbitrability, after which MSD may file a renewed motion to compel arbitration. Patent Litigation From time to time, generic manufacturers of pharmaceutical products file abbreviated New Drug Applications (NDAs) 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. Januvia, Janumet, Janumet XR — In February 2019, Par Pharmaceutical, Inc. (Par Pharmaceutical) filed suit against the Company in the U.S. District Court for the District of New Jersey, seeking a declaratory judgment of invalidity of a patent owned by the Company covering certain salt and polymorphic forms of sitagliptin that expires in 2026. In response, the Company filed a patent infringement lawsuit in the U.S. District Court for the District of Delaware against Par Pharmaceutical and additional companies that also indicated an intent to market generic versions of Januvia , Janumet , and Janumet XR following expiration of key patent protection in 2022, but prior to the expiration of the later-granted patent owned by the Company covering certain salt and polymorphic forms of sitagliptin that expires in 2026, and a later granted patent owned by the Company covering the Janumet formulation which expires in 2028. Par Pharmaceutical dismissed its case in the U.S. District Court for the District of New Jersey against the Company and will litigate the action in the U.S. District Court for the District of Delaware. The Company filed a patent infringement lawsuit against Mylan Pharmaceuticals Inc. and Mylan Inc. (Mylan) in the Northern District of West Virginia. The Judicial Panel of Multidistrict Litigation entered an order transferring the Company’s lawsuit against Mylan to the U.S. District Court for the District of Delaware for coordinated and consolidated pretrial proceedings with the other cases pending in that district. The U.S. District Court for the District of Delaware has scheduled the lawsuits for a single 3-day trial on invalidity issues in October 2021. The Court will schedule separate 1-day trials on infringement issues if necessary. In October 2019, Mylan filed a petition for Inter Partes Review (IPR) at the United States Patent and Trademark Office (USPTO) seeking invalidity of the 2026 patent. The USPTO has six months from filing to determine whether it will institute the requested IPR proceeding. 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 September 30, 2019 and December 31, 2018 of approximately $260 million and $245 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.

Equity

Equity	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Equity	Equity Three Months Ended September 30, Common Stock Other Paid-In Capital Retained Earnings Accumulated Other Comprehensive Loss Treasury Stock Non- controlling Interests Total ($ and shares in millions except per share amounts) Shares Par Value Shares Cost Balance at July 1, 2018 3,577 $ 1,788 $ 39,741 $ 41,523 $ (5,122 ) 907 $ (45,401 ) $ 237 $ 32,766 Net income attributable to Merck & Co., Inc. — — — 1,950 — — — — 1,950 Other comprehensive loss, net of taxes — — — — (29 ) — — — (29 ) Cash dividends declared on common stock ($0.48 per share) — — — (1,284 ) — — — — (1,284 ) Treasury stock shares purchased — — — — — 16 (996 ) — (996 ) Share-based compensation plans and other — — 21 — — (5 ) 231 — 252 Net income attributable to noncontrolling interests — — — — — — — 8 8 Distributions attributable to noncontrolling interests — — — — — — — (11 ) (11 ) Balance at September 30, 2018 3,577 $ 1,788 $ 39,762 $ 42,189 $ (5,151 ) 918 $ (46,166 ) $ 234 $ 32,656 Balance at July 1, 2019 3,577 $ 1,788 $ 39,484 $ 45,295 $ (5,362 ) 1,010 $ (53,570 ) $ 102 $ 27,737 Net income attributable to Merck & Co., Inc. — — — 1,901 — — — — 1,901 Other comprehensive loss, net of taxes — — — — (28 ) — — — (28 ) Cash dividends declared on common stock ($0.55 per share) — — — (1,392 ) — — — — (1,392 ) Treasury stock shares purchased — — — — — 17 (1,405 ) — (1,405 ) Share-based compensation plans and other — — 77 — — (1 ) 50 — 127 Net income attributable to noncontrolling interests — — — — — — — 6 6 Distributions attributable to noncontrolling interests — — — — — — — (21 ) (21 ) Balance at September 30, 2019 3,577 $ 1,788 $ 39,561 $ 45,804 $ (5,390 ) 1,026 $ (54,925 ) $ 87 $ 26,925 Nine Months Ended September 30, Common Stock Other Paid-In Capital Retained Earnings Accumulated Other Comprehensive Loss Treasury Stock Non- controlling Interests Total ($ and shares in millions except per share amounts) Shares Par Value Shares Cost Balance at January 1, 2018 3,577 $ 1,788 $ 39,902 $ 41,350 $ (4,910 ) 880 $ (43,794 ) $ 233 $ 34,569 Net income attributable to Merck & Co., Inc. — — — 4,393 — — — — 4,393 Adoption of new accounting standards — — — 322 (274 ) — — — 48 Other comprehensive income, net of taxes — — — — 33 — — — 33 Cash dividends declared on common stock ($1.44 per share) — — — (3,876 ) — — — — (3,876 ) Treasury stock shares purchased — — — — — 53 (3,158 ) — (3,158 ) Share-based compensation plans and other — — (140 ) — — (15 ) 786 — 646 Net income attributable to noncontrolling interests — — — — — — — 22 22 Distributions attributable to noncontrolling interests — — — — — — — (21 ) (21 ) Balance at September 30, 2018 3,577 $ 1,788 $ 39,762 $ 42,189 $ (5,151 ) 918 $ (46,166 ) $ 234 $ 32,656 Balance at January 1, 2019 3,577 $ 1,788 $ 38,808 $ 42,579 $ (5,545 ) 985 $ (50,929 ) $ 181 $ 26,882 Net income attributable to Merck & Co., Inc. — — — 7,487 — — — — 7,487 Other comprehensive income, net of taxes — — — — 155 — — — 155 Cash dividends declared on common stock ($1.65 per share) — — — (4,262 ) — — — — (4,262 ) Treasury stock shares purchased — — 1,000 — — 54 (4,730 ) — (3,730 ) Share-based compensation plans and other — — (247 ) — — (13 ) 734 — 487 Net loss attributable to noncontrolling interests — — — — — — — (73 ) (73 ) Distributions attributable to noncontrolling interests — — — — — — — (21 ) (21 ) Balance at September 30, 2019 3,577 $ 1,788 $ 39,561 $ 45,804 $ (5,390 ) 1,026 $ (54,925 ) $ 87 $ 26,925 On October 25, 2018, the Company entered into accelerated share repurchase (ASR) agreements with two third-party financial institutions (Dealers). Under the ASR agreements, Merck agreed to purchase $5 billion of Merck’s common stock, in total, with an initial delivery of 56.7 million shares of Merck’s common stock, based on the then-current market price, made by the Dealers to Merck, and payments of $5 billion made by Merck to the Dealers on October 29, 2018, which were funded with existing cash and investments, as well as short-term borrowings. The payments to the Dealers were recorded as reductions to shareholders’ equity, consisting of a $4 billion increase in treasury stock, which reflected the value of the initial 56.7 million shares received on October 29, 2018, and a $1 billion decrease in other-paid-in capital, which reflected the value of the stock held back by the Dealers pending final settlement. Upon settlement of the ASR agreements in April 2019, Merck received an additional 7.7 million shares as determined by the average daily volume weighted-average price of Merck’s common stock during the term of the ASR program, less a negotiated discount, bringing the total shares received by Merck under this program to 64.4 million

Share-Based Compensation Plans

Share-Based Compensation Plans	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [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 Nine Months Ended ($ in millions) 2019 2018 2019 2018 Pretax share-based compensation expense $ 101 $ 91 $ 306 $ 261 Income tax benefit (14 ) (14 ) (42 ) (42 ) Total share-based compensation expense, net of taxes $ 87 $ 77 $ 264 $ 219 During the first nine months of 2019 , the Company granted 5 million RSUs with a weighted-average grant date fair value of $80.03 per RSU and during the first nine months of 2018 granted 7 million RSUs with a weighted-average grant date fair value of $58.19 per RSU. During the first nine months of 2019 , the Company granted 609 thousand PSUs with a weighted-average grant date fair value of $90.50 per PSU and during the first nine months of 2018 granted 855 thousand PSUs with a weighted-average grant date fair value of $56.70 per PSU. During the first nine months of 2019 , the Company granted 3 million stock options with a weighted-average exercise price of $80.05 per option and during the first nine months of 2018 granted 3 million stock options with a weighted-average exercise price of $57.72 per option. The weighted-average fair value of options granted during the first nine months of 2019 and 2018 was $10.63 and $8.19 per option, respectively, and was determined using the following assumptions: Nine Months Ended 2019 2018 Expected dividend yield 3.2 % 3.4 % Risk-free interest rate 2.4 % 2.8 % Expected volatility 18.7 % 19.1 % Expected life (years) 5.9 6.1 At September 30, 2019 , there was $691 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 2.0 years . For segment reporting, share-based compensation costs are unallocated expenses.

Pension and Other Postretiremen

Pension and Other Postretirement Benefit Plans	9 Months Ended
	Sep. 30, 2019
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 of such plans consisted of the following components: Three Months Ended Nine Months Ended 2019 2018 2019 2018 ($ in millions) U.S. International U.S. International U.S. International U.S. International Service cost $ 76 $ 58 $ 77 $ 56 $ 221 $ 178 $ 245 $ 181 Interest cost 115 44 109 43 343 133 324 134 Expected return on plan assets (202 ) (106 ) (209 ) (106 ) (613 ) (320 ) (634 ) (326 ) Amortization of unrecognized prior service credit (12 ) (3 ) (12 ) (3 ) (37 ) (9 ) (37 ) (10 ) Net loss amortization 43 16 63 21 113 47 174 64 Termination benefits 3 — 1 — 7 1 18 — Curtailments 5 — 3 — 6 — 7 (1 ) Settlements — — — — — — 1 3 $ 28 $ 9 $ 32 $ 11 $ 40 $ 30 $ 98 $ 45 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 credit of such plans consisted of the following components: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Service cost $ 12 $ 15 $ 36 $ 43 Interest cost 17 17 52 52 Expected return on plan assets (18 ) (21 ) (54 ) (63 ) Amortization of unrecognized prior service credit (20 ) (21 ) (59 ) (63 ) Net loss amortization (3 ) — (7 ) 1 Termination benefits 1 — 1 2 Curtailments (3 ) (1 ) (4 ) (7 ) $ (14 ) $ (11 ) $ (35 ) $ (35 ) In connection with restructuring actions (see Note 4), 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 and settlements 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 13), with the exception of certain amounts for termination benefits, curtailments and settlements, which are recorded in Restructuring costs if the event giving rise to the termination benefits, curtailment or settlement is related to restructuring actions as noted above.

Other (Income) Expense, Net

Other (Income) Expense, Net	9 Months Ended
	Sep. 30, 2019
Other Income and Expenses [Abstract]
Other (Income) Expense, Net	Other (Income) Expense, Net Other (income) expense, net, consisted of: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Interest income $ (61 ) $ (92 ) $ (225 ) $ (257 ) Interest expense 231 190 674 569 Exchange losses 38 42 166 119 Income from investments in equity securities, net (1) (16 ) (198 ) (50 ) (376 ) Net periodic defined benefit plan (credit) cost other than service cost (128 ) (119 ) (409 ) (384 ) Other, net (29 ) 5 206 (183 ) $ 35 $ (172 ) $ 362 $ (512 ) (1) Includes net realized and unrealized gains and losses from investments in equity securities either owned directly or through ownership interests in investments funds. The higher exchange losses in the first nine months of 2019 reflect losses on forward exchange contracts related to the acquisition of Antelliq. Other, net (as reflected in the table above) in the first nine months of 2019 includes $162 million of goodwill impairment charges related to certain businesses in the Healthcare Services segment. Other, net in the first nine months of 2018 includes a $115 million gain on the settlement of certain patent litigation and $84 million of income related to AstraZeneca’s option exercise associated with AstraZeneca LP. Interest paid for the nine months ended September 30, 2019 and 2018 was $629 million and $535 million , respectively.

Taxes on Income

Taxes on Income	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Taxes on Income	Taxes on Income The effective income tax rates of 18.7% and 26.5% for the third quarter of 2019 and 2018 , respectively, and 14.5% and 27.6% for the first nine months of 2019 and 2018, respectively, reflect the impacts of acquisition and divestiture-related costs and restructuring costs, partially offset by the beneficial impact of foreign earnings. The effective income tax rates in the third quarter and first nine months of 2019 also reflect the unfavorable impact of a charge for the acquisition of Peloton for which no tax benefit was recognized and the favorable impact of product mix on the estimated full-year tax rate. In addition, the effective income tax rate for the first nine months of 2019 reflects the favorable impact of a $360 million net tax benefit related to the settlement of certain federal income tax matters (discussed below). The effective income tax rate for the first nine months of 2018 reflects the unfavorable impact of a charge recorded in connection with the formation of a collaboration with Eisai for which no tax benefit was recognized. In the first quarter of 2019, the Internal Revenue Service (IRS) concluded its examinations of Merck’s 2012-2014 U.S. federal income tax returns. As a result, the Company was required to make a payment of $107 million . The Company’s reserves for unrecognized tax benefits for the years under examination exceeded the adjustments relating to this examination period and therefore the Company recorded a $360 million net tax benefit in the first nine months of 2019. This net benefit reflects reductions in reserves for unrecognized tax benefits for tax positions relating to the years that were under examination, partially offset by additional reserves for tax positions not previously reserved for.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share The calculations of earnings per share are as follows: Three Months Ended Nine Months Ended ($ and shares in millions except per share amounts) 2019 2018 2019 2018 Net income attributable to Merck & Co., Inc. $ 1,901 $ 1,950 $ 7,487 $ 4,393 Average common shares outstanding 2,558 2,662 2,572 2,680 Common shares issuable (1) 14 16 15 14 Average common shares outstanding assuming dilution 2,572 2,678 2,587 2,694 Basic earnings per common share attributable to Merck & Co., Inc. common shareholders $ 0.74 $ 0.73 $ 2.91 $ 1.64 Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders $ 0.74 $ 0.73 $ 2.89 $ 1.63 (1) Issuable primarily under share-based compensation plans. For the third quarter of 2019 and 2018 , 3 million and 2 million , respectively, and for the first nine months of 2019 and 2018 , 2 million and 7 million

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Changes in AOCI by component are as follows: Three Months Ended September 30, ($ in millions) Derivatives Investments Employee Benefit Plans Cumulative Translation Adjustment Accumulated Other Comprehensive Income (Loss) Balance July 1, 2018, net of taxes $ 65 $ (164 ) $ (3,065 ) $ (1,958 ) $ (5,122 ) Other comprehensive income (loss) before reclassification adjustments, pretax 29 8 — (147 ) (110 ) Tax (6 ) — — 11 5 Other comprehensive income (loss) before reclassification adjustments, net of taxes 23 8 — (136 ) (105 ) Reclassification adjustments, pretax 5 (1) 32 (2) 47 (3) — 84 Tax (1 ) — (7 ) — (8 ) Reclassification adjustments, net of taxes 4 32 40 — 76 Other comprehensive income (loss), net of taxes 27 40 40 (136 ) (29 ) Balance September 30, 2018, net of taxes $ 92 $ (124 ) $ (3,025 ) $ (2,094 ) $ (5,151 ) Balance July 1, 2019, net of taxes $ 66 $ 48 $ (3,530 ) $ (1,946 ) $ (5,362 ) Other comprehensive income (loss) before reclassification adjustments, pretax 186 8 (4 ) (84 ) 106 Tax (39 ) — — (33 ) (72 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes 147 8 (4 ) (117 ) 34 Reclassification adjustments, pretax (71 ) (1) (25 ) (2) 21 (3) — (75 ) Tax 15 — (2 ) — 13 Reclassification adjustments, net of taxes (56 ) (25 ) 19 — (62 ) Other comprehensive income (loss), net of taxes 91 (17 ) 15 (117 ) (28 ) Balance September 30, 2019, net of taxes $ 157 $ 31 $ (3,515 ) $ (2,063 ) $ (5,390 ) Nine Months Ended September 30, ($ in millions) Derivatives Investments Employee Benefit Plans Cumulative Translation Adjustment Accumulated Other Comprehensive Income (Loss) Balance January 1, 2018, net of taxes $ (108 ) $ (61 ) $ (2,787 ) $ (1,954 ) $ (4,910 ) Other comprehensive income (loss) before reclassification adjustments, pretax 113 (125 ) (2 ) (129 ) (143 ) Tax (24 ) 1 4 (111 ) (130 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes 89 (124 ) 2 (240 ) (273 ) Reclassification adjustments, pretax 169 (1) 68 (2) 128 (3) — 365 Tax (35 ) — (24 ) — (59 ) Reclassification adjustments, net of taxes 134 68 104 — 306 Other comprehensive income (loss), net of taxes 223 (56 ) 106 (240 ) 33 Adoption of ASU 2018-02 (23 ) 1 (344 ) 100 (266 ) Adoption of ASU 2016-01 — (8 ) — — (8 ) Balance September 30, 2018, net of taxes $ 92 $ (124 ) $ (3,025 ) $ (2,094 ) $ (5,151 ) Balance January 1, 2019, net of taxes $ 166 $ (78 ) $ (3,556 ) $ (2,077 ) $ (5,545 ) Other comprehensive income (loss) before reclassification adjustments, pretax 183 139 (5 ) 47 364 Tax (38 ) — 6 (33 ) (65 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes 145 139 1 14 299 Reclassification adjustments, pretax (195 ) (1) (30 ) (2) 49 (3) — (176 ) Tax 41 — (9 ) — 32 Reclassification adjustments, net of taxes (154 ) (30 ) 40 — (144 ) Other comprehensive income (loss), net of taxes (9 ) 109 41 14 155 Balance September 30, 2019, net of taxes $ 157 $ 31 $ (3,515 ) $ (2,063 ) $ (5,390 ) (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 debt securities that were reclassified from AOCI to Other (income) expense, net . (3) Includes net amortization of prior service cost and actuarial gains and losses included in net periodic benefit cost (see Note 12).

Segment Reporting

Segment Reporting	9 Months Ended
	Sep. 30, 2019
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 Pharmaceutical segment includes human health pharmaceutical and vaccine products. Human health pharmaceutical products consist of therapeutic and preventive agents, generally sold by prescription, for the treatment of human disorders. The Company sells these human health pharmaceutical products primarily to drug wholesalers and retailers, hospitals, government agencies and managed health care providers such as health maintenance organizations, pharmacy benefit managers and other institutions. Human health vaccine products consist of preventive pediatric, adolescent and adult vaccines, primarily administered at physician offices. The Company sells these human health vaccines primarily to physicians, wholesalers, physician distributors and government entities. A large component of pediatric and adolescent vaccine sales are made to the U.S. Centers for Disease Control and Prevention Vaccines for Children program, which is funded by the U.S. government. Additionally, the Company sells vaccines to the Federal government for placement into vaccine stockpiles. During 2019, as a result of changes to the Company’s internal reporting structure, certain costs that were previously included in the Pharmaceutical segment are now being included as part of non-segment expenses within Merck Research Laboratories. Prior period Pharmaceutical segment profits have been recast to reflect these changes on a comparable basis. The Animal Health segment discovers, develops, manufactures and markets animal health products, including pharmaceutical and vaccine products, for the prevention, treatment and control of disease in all major livestock and companion animal species, which the Company sells to veterinarians, distributors and animal producers. The Healthcare Services segment provides services and solutions that focus on engagement, health analytics and clinical services to improve the value of care delivered to patients. The Alliances segment primarily includes activity from the Company’s relationship with AstraZeneca LP related to sales of Nexium and Prilosec, which concluded in 2018. Sales of the Company’s products were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 ($ in millions) U.S. Int’l Total U.S. Int’l Total U.S. Int’l Total U.S. Int’l Total Pharmaceutical: Oncology Keytruda $ 1,743 $ 1,327 $ 3,070 $ 1,109 $ 780 $ 1,889 $ 4,525 $ 3,448 $ 7,973 $ 2,906 $ 2,114 $ 5,020 Emend 42 56 98 71 52 123 173 163 336 239 157 396 Alliance revenue - Lynparza 71 53 123 33 15 49 186 126 313 88 37 125 Alliance revenue - Lenvima 65 44 109 30 13 43 169 112 280 49 29 78 Vaccines Gardasil/Gardasil 9 761 558 1,320 740 308 1,048 1,579 1,464 3,044 1,422 894 2,317 ProQuad/M-M-R II /Varivax 482 141 623 429 96 525 1,325 469 1,794 1,097 246 1,343 Pneumovax 23 179 58 237 160 54 214 428 164 592 394 192 586 RotaTeq 102 78 180 134 57 191 360 203 564 384 156 540 Vaqta 36 26 62 36 30 66 103 65 167 95 72 167 Hospital Acute Care Bridion 133 151 284 96 120 217 381 437 817 272 389 661 Noxafil 77 100 177 89 99 188 268 291 560 257 294 551 Cubicin 14 38 52 55 40 95 78 129 207 150 137 287 Primaxin 2 75 77 1 71 72 2 204 207 6 206 212 Invanz (1 ) 58 57 74 62 137 30 176 206 252 185 437 Cancidas — 62 62 2 77 79 5 187 191 10 247 257 Immunology Simponi — 203 203 — 210 210 — 625 625 — 673 673 Remicade — 101 101 — 135 135 — 322 322 — 459 459 Neuroscience Belsomra 23 57 80 23 43 66 68 155 223 76 115 191 Virology Isentress/Isentress HD 102 149 250 123 151 275 304 449 752 383 477 860 Zepatier 24 59 83 18 86 104 96 208 304 8 339 347 Cardiovascular Zetia 5 142 147 9 157 165 11 432 443 34 662 696 Vytorin 5 52 57 — 92 92 11 219 231 11 402 414 Atozet — 97 97 — 84 84 — 283 283 — 258 258 Adempas — 107 107 — 94 94 — 302 302 — 238 238 Diabetes Januvia 367 440 807 498 429 927 1,223 1,317 2,539 1,466 1,291 2,756 Janumet 129 375 503 225 339 563 462 1,105 1,567 625 1,067 1,693 Women’s Health NuvaRing 202 39 241 193 41 234 593 107 700 550 135 686 Implanon/Nexplanon 136 62 199 133 53 186 421 160 581 375 160 535 Diversified Brands Singulair 11 140 152 5 156 161 24 479 503 16 505 521 Cozaar/Hyzaar 6 110 116 4 99 103 16 313 329 18 330 348 Nasonex 4 55 58 7 64 71 2 224 226 8 266 274 Arcoxia — 72 72 — 83 83 — 221 221 — 249 249 Follistim AQ 27 35 62 26 34 60 80 102 182 83 115 198 Other pharmaceutical (1) 385 842 1,229 326 786 1,109 1,142 2,492 3,634 932 2,557 3,486 Total Pharmaceutical segment sales 5,132 5,962 11,095 4,649 5,010 9,658 14,065 17,153 31,218 12,206 15,653 27,859 Animal Health: Livestock 144 582 726 153 508 660 406 1,601 2,007 383 1,563 1,946 Companion Animals 193 203 396 153 207 361 560 704 1,264 541 689 1,230 Total Animal Health segment sales 337 785 1,122 306 715 1,021 966 2,305 3,271 924 2,252 3,176 Other segment sales (2) 46 — 46 55 — 55 133 1 133 194 1 195 Total segment sales 5,515 6,747 12,263 5,010 5,725 10,734 15,164 19,459 34,622 13,324 17,906 31,230 Other (3) 10 125 134 20 39 60 19 330 350 101 (35 ) 66 $ 5,525 $ 6,872 $ 12,397 $ 5,030 $ 5,764 $ 10,794 $ 15,183 $ 19,789 $ 34,972 $ 13,425 $ 17,871 $ 31,296 U.S. plus international may not equal total due to rounding . (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. Product sales are recorded net of the provision for discounts, including chargebacks, which are customer discounts that occur when a contracted customer purchases through an intermediary wholesale purchaser, and rebates that are 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. These discounts, in the aggregate, reduced U.S. sales by $3.0 billion and $2.6 billion for the three months ended September 30, 2019 and 2018 , respectively, and by $8.6 billion and $7.7 billion for the nine months ended September 30, 2019 and 2018 , respectively. Consolidated sales by geographic area where derived are as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 United States $ 5,525 $ 5,030 $ 15,183 $ 13,425 Europe, Middle East and Africa 3,189 2,884 9,452 9,218 Japan 919 761 2,639 2,353 China 914 512 2,423 1,556 Asia Pacific (other than Japan and China) 756 666 2,217 2,210 Latin America 671 622 1,889 1,748 Other 423 319 1,169 786 $ 12,397 $ 10,794 $ 34,972 $ 31,296 A reconciliation of segment profits to Income before taxes is as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Segment profits: Pharmaceutical segment $ 7,747 $ 6,621 $ 21,437 $ 18,535 Animal Health segment 423 409 1,243 1,273 Other segments (2 ) 5 (2 ) 94 Total segment profits 8,168 7,035 22,678 19,902 Other profits (losses) 101 55 226 (35 ) Unallocated: Interest income 61 92 225 257 Interest expense (231 ) (190 ) (674 ) (569 ) Depreciation and amortization (382 ) (324 ) (1,169 ) (1,006 ) Research and development (3,110 ) (1,997 ) (7,045 ) (7,304 ) Amortization of purchase accounting adjustments (329 ) (679 ) (1,105 ) (2,144 ) Restructuring costs (232 ) (171 ) (444 ) (494 ) Charge related to termination of collaboration agreement with Samsung — (420 ) — (420 ) Other unallocated, net (1,699 ) (736 ) (4,019 ) (2,090 ) $ 2,347 $ 2,665 $ 8,673 $ 6,097 Pharmaceutical segment profits are comprised of segment sales less standard costs, as well as selling, general and administrative expenses directly incurred by the segment. Animal Health segment profits are comprised of segment sales, less all cost of sales, as well as selling, general and administrative expenses and research and development costs directly incurred by the segment. For internal management reporting presented to the chief operating decision maker, Merck does not allocate the remaining cost of sales not included in segment profits as described above, research and development expenses incurred in Merck Research Laboratories, the Company’s research and development division that focuses on human health-related activities, or general and administrative expenses, nor the cost of financing these activities. Separate divisions maintain responsibility for monitoring and managing these costs, including depreciation related to fixed assets utilized by these divisions and, therefore, they are not included in segment profits. Also excluded from the determination of segment profits are costs related to restructuring activities, as well as the amortization of purchase accounting adjustments. Other profits are primarily comprised of miscellaneous corporate profits, as well as operating profits related to third-party manufacturing sales. Other unallocated, net, includes expenses from corporate and manufacturing cost centers, goodwill and other intangible asset impairment charges, gains or losses on sales of businesses, expense or income related to changes in the estimated fair value measurement of liabilities for contingent consideration, and other miscellaneous income or expense items.

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2019
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, 2019. 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 February 2016, the Financial Accounting Standards Board (FASB) issued new accounting guidance for the accounting and reporting of leases (ASU 2016-02) and subsequently issued several updates to the new guidance (ASC 842 or new guidance). The new guidance requires that lessees recognize a right-of-use asset and a lease liability for each of its leases (other than leases that meet the definition of a short-term lease). Leases are classified as either operating or finance. Operating leases result in straight-line expense in the income statement (similar to previous operating leases), while finance leases result in more expense being recognized in the earlier years of the lease term (similar to previous capital leases). The Company adopted the new standard on January 1, 2019 using a modified retrospective approach. Merck elected the transition method that allows for application of the standard at the adoption date rather than at the beginning of the earliest comparative period presented in the financial statements. The Company also elected available practical expedients. Upon adoption, the Company recognized $1.1 billion of additional assets and related liabilities on its consolidated balance sheet (see Note 8). The adoption of the new guidance did not impact the Company’s consolidated statements of income or cash flows. In April 2018, the FASB issued new guidance on the accounting for costs incurred to implement a cloud computing arrangement that is considered a service arrangement. The new guidance requires the capitalization of such costs, aligning it with the accounting for costs associated with developing or obtaining internal-use software. The Company adopted the new standard in the third quarter of 2019 using prospective application for eligible costs, which were immaterial. Recently Issued Accounting Standards Not Yet Adopted 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, including adoption in any interim period. The new guidance is to be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings in the beginning of the period of adoption. The Company is continuing to assess the impact of adopting the new standard but does not expect the adoption to have a material impact on its consolidated financial statements, subject to the finalization of its assessment. In November 2018, the FASB issued new guidance for collaborative arrangements intended to reduce diversity in practice by clarifying whether certain transactions between collaborative arrangement participants should be accounted for under revenue recognition guidance (ASC 606). The new guidance is effective for interim and annual periods beginning in 2020. Early adoption is permitted, including adoption in any interim period. The new guidance is to be applied on a retrospective basis through a cumulative-effect adjustment directly to retained earnings. The Company does not anticipate the adoption of this standard will have a material effect on its consolidated financial statements.

Contingencies Commitments and C

Contingencies Commitments and Contingencies (Policies)	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Legal Costs, Policy	Legal defense costs expected to be incurred in connection with a loss contingency are accrued when probable and reasonably estimable.

Acquisitions, Divestitures, R_2

Acquisitions, Divestitures, Research Collaborations and License Agreements (Tables)	9 Months Ended
	Sep. 30, 2019
Business Combinations [Abstract]
Fair Value of Assets Acquired and Liabilities Assumed	The estimated fair value of assets acquired and liabilities assumed from Antelliq is as follows: ($ in millions) April 1, 2019 Cash and cash equivalents $ 31 Accounts receivable 73 Inventories 95 Property, plant and equipment 62 Identifiable intangible assets (useful lives ranging from 18-24 years) (1) 2,689 Deferred income tax liabilities (563 ) Other assets and liabilities, net (81 ) Total identifiable net assets 2,306 Goodwill (2) 1,345 Consideration transferred $ 3,651 (1) The estimated fair values of identifiable intangible assets relate primarily to trade names and were determined using an income approach. The future net cash flows were discounted to present value utilizing a discount rate of 11.5% . Actual cash flows are likely to be different than those assumed. (2) The goodwill recognized is largely attributable to anticipated synergies expected to arise after the acquisition and was allocated to the Animal Health segment. The goodwill is not deductible for tax purposes.

Collaborative Arrangements (Tab

Collaborative Arrangements (Tables)	9 Months Ended
	Sep. 30, 2019
Collaborative Arrangements [Abstract]
Collaboration Arrangements	Summarized financial information related to this collaboration is as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Alliance revenue $ 109 $ 43 $ 280 $ 78 Cost of sales (1) 23 8 97 9 Selling, general and administrative 21 5 59 7 Research and development (2) 37 36 146 1,473 ($ in millions) September 30, 2019 December 31, 2018 Receivables from Eisai included in Other current assets $ 109 $ 71 Payables to Eisai included in Accrued and other current liabilities (3) 692 375 Payables to Eisai included in Other Noncurrent Liabilities (3) 125 543 (1) Represents amortization of capitalized milestone payments. (2) Amount for the first nine months of 2018 includes the upfront payment and future option payments. (3) Includes accrued milestone and option payments. Summarized financial information related to this collaboration is as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Alliance revenue $ 123 $ 49 $ 313 $ 125 Cost of sales (1) 28 12 120 48 Selling, general and administrative 36 12 96 28 Research and development 44 47 122 118 ($ in millions) September 30, 2019 December 31, 2018 Receivables from AstraZeneca included in Other current assets $ 119 $ 52 Payables to AstraZeneca included in Accrued and other current liabilities (2) 578 405 Payables to AstraZeneca included in Other Noncurrent Liabilities (3) 300 250 (1) Represents amortization of capitalized milestone payments. (2) Includes accrued milestone and license option payments. (3) Includes accrued milestone payments. Summarized financial information related to this collaboration is as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Net product sales recorded by Merck $ 57 $ 47 $ 158 $ 138 Merck’s profit share from sales in Bayer’s marketing territories 50 47 144 100 Total sales 107 94 302 238 Cost of sales (1) 28 29 86 188 Selling, general and administrative 12 11 31 26 Research and development 31 34 94 90 ($ in millions) September 30, 2019 December 31, 2018 Receivables from Bayer included in Other current assets $ 44 $ 32 Payables to Bayer included in Other Noncurrent Liabilities (2) 375 375 (1) Includes amortization of intangible assets. (2) Represents accrued milestone payment.

Restructuring (Tables)

Restructuring (Tables)	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 Nine Months Ended September 30, 2019 ($ in millions) Separation Costs Accelerated Depreciation Other Total Separation Costs Accelerated Depreciation Other Total Cost of sales $ — $ 41 $ 21 $ 62 $ — $ 139 $ 22 $ 161 Selling, general and administrative — 1 — 1 — 33 — 33 Research and development — (1 ) 2 1 — 1 3 4 Restructuring costs 205 — 27 232 358 — 86 444 $ 205 $ 41 $ 50 $ 296 $ 358 $ 173 $ 111 $ 642 Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 ($ in millions) Separation Costs Accelerated Depreciation Other Total Separation Costs Accelerated Depreciation Other Total Cost of sales $ — $ 1 $ 1 $ 2 $ — $ 1 $ 10 $ 11 Selling, general and administrative — — — — — 1 1 2 Research and development — (9 ) 5 (4 ) — (12 ) 13 1 Restructuring costs 137 — 34 171 392 — 102 494 $ 137 $ (8 ) $ 40 $ 169 $ 392 $ (10 ) $ 126 $ 508
Charges and Spending Relating to Restructuring Activities by Program	The following table summarizes the charges and spending relating to restructuring program activities for the nine months ended September 30, 2019 : ($ in millions) Separation Costs Accelerated Depreciation Other Total Restructuring reserves January 1, 2019 $ 443 $ — $ 91 $ 534 Expense 358 173 111 642 (Payments) receipts, net (198 ) — (158 ) (356 ) Non-cash activity — (173 ) 20 (153 ) Restructuring reserves September 30, 2019 (1) $ 603 $ — $ 64 $ 667 (1)

Financial Instruments (Tables)

Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Effect of Net Investment Hedges on OCI and the Consolidated Statement of Income	The effects of the Company’s net investment hedges on OCI and the Consolidated Statement of Income are shown below: Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income (1) Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing Three Months Ended September 30, Nine Months Ended September 30, Three Months Ended September 30, Nine Months Ended September 30, ($ in millions) 2019 2018 2019 2018 2019 2018 2019 2018 Net Investment Hedging Relationships Foreign exchange contracts $ 1 $ (10 ) $ 8 $ (24 ) $ (8 ) $ (4 ) $ (23 ) $ (7 ) Euro-denominated notes (150 ) 38 (152 ) (54 ) — — — — (1) No amounts were reclassified from AOCI into income related to the sale of a subsidiary.
Summary of Interest Rate Swaps Held	At September 30, 2019 , the Company was a party to 19 pay-floating, receive-fixed interest rate swap contracts designated as fair value hedges of fixed-rate notes in which the notional amounts match the amount of the hedged fixed-rate notes as detailed in the table below. September 30, 2019 ($ in millions) Par Value of Debt Number of Interest Rate Swaps Held Total Swap Notional Amount 1.85% notes due 2020 $ 1,250 5 $ 1,250 3.875% notes due 2021 1,150 5 1,150 2.40% notes due 2022 1,000 4 1,000 2.35% notes due 2022 1,250 5 1,250
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 Liabilities Cumulative Amount of Fair Value Hedging Adjustment Increase (Decrease) Included in the Carrying Amount ($ in millions) September 30, 2019 December 31, 2018 September 30, 2019 December 31, 2018 Balance Sheet Line Item in which Hedged Item is Included Loans payable and current portion of long-term debt $ 1,247 $ — $ (3 ) $ — Long-Term Debt 3,416 4,560 22 (82 )
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: September 30, 2019 December 31, 2018 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 $ 22 $ — $ 3,400 $ — $ — $ — Interest rate swap contracts Accrued and other current liabilities — 3 1,250 — — — Interest rate swap contracts Other Noncurrent Liabilities — — — — 81 4,650 Foreign exchange contracts Other current assets 252 — 7,144 263 — 6,222 Foreign exchange contracts Other Assets 56 — 2,073 75 — 2,655 Foreign exchange contracts Accrued and other current liabilities — 6 775 — 7 774 Foreign exchange contracts Other Noncurrent Liabilities — 1 9 — 1 89 $ 330 $ 10 $ 14,651 $ 338 $ 89 $ 14,390 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts Other current assets $ 153 $ — $ 6,802 $ 116 $ — $ 5,430 Foreign exchange contracts Accrued and other current liabilities — 100 6,906 — 71 9,922 $ 153 $ 100 $ 13,708 $ 116 $ 71 $ 15,352 $ 483 $ 110 $ 28,359 $ 454 $ 160 $ 29,742
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: September 30, 2019 December 31, 2018 ($ in millions) Asset Liability Asset Liability Gross amounts recognized in the condensed consolidated balance sheet $ 483 $ 110 $ 454 $ 160 Gross amounts subject to offset in master netting arrangements not offset in the condensed consolidated balance sheet (73 ) (73 ) (121 ) (121 ) Cash collateral received (133 ) — (107 ) — Net amounts $ 277 $ 37 $ 226 $ 39
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: Sales Other (income) expense, net (1) Other comprehensive income (loss) Sales Other (income) expense, net (1) Other comprehensive income (loss) Three Months Ended September 30, Three Months Ended September 30, Three Months Ended September 30, Nine Months Ended September 30, Nine Months Ended September 30, Nine Months Ended September 30, ($ in millions) 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 Financial Statement Line Items in which Effects of Fair Value or Cash Flow Hedges are Recorded $ 12,397 $ 10,794 $ 35 $ (172 ) $ (28 ) $ (29 ) $ 34,972 $ 31,296 $ 362 $ (512 ) $ 155 $ 33 (Gain) loss on fair value hedging relationships Interest rate swap contracts Hedged items — — 13 (9 ) — — — — 101 (86 ) — — Derivatives designated as hedging instruments — — (6 ) 15 — — — — (74 ) 100 — — Impact of cash flow hedging relationships Foreign exchange contracts Amount of income (loss) recognized in OCI on derivatives — — — — 186 29 — — — — 183 113 Increase (decrease) in Sales as a result of AOCI reclassifications 70 (6 ) — — (70 ) 6 189 (172 ) — — (189 ) 172 Interest rate contracts Amount of gain recognized in Other (income) expense, net on derivatives — — (1 ) (1 ) — — — — (3 ) (3 ) — — Amount of loss recognized in OCI on derivatives — — — — (1 ) (1 ) — — — — (6 ) (3 ) (1) Interest expense is a component of Other (income) expense, net.
Income Statement Effects of Derivatives Not Designated as Hedging Instruments	The table below provides information regarding the income statement effects of derivatives not designated as hedging instruments: Amount of Derivative Pretax (Gain) Loss Recognized in Income Three Months Ended September 30, Nine Months Ended September 30, ($ in millions) Income Statement Caption 2019 2018 2019 2018 Derivatives Not Designated as Hedging Instruments Foreign exchange contracts (1) Other (income) expense, net $ (8 ) $ (57 ) $ 112 $ (224 ) Foreign exchange contracts (2) Sales (11 ) — (7 ) (5 ) (1) These derivative contracts mitigate changes in the value of remeasured foreign currency denominated monetary assets and liabilities attributable to changes in foreign currency exchange rates. (2) These derivative contracts serve as economic hedges of forecasted transactions.
Information on Investments in Debt and Equity Securities	Information on investments in debt and equity securities is as follows: September 30, 2019 December 31, 2018 Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized Fair Value ($ in millions) Gains Losses Gains Losses Corporate notes and bonds $ 1,260 $ 24 $ — $ 1,284 $ 4,985 $ 3 $ (68 ) $ 4,920 Asset-backed securities 434 3 — 437 1,285 1 (11 ) 1,275 U.S. government and agency securities 358 4 — 362 895 2 (5 ) 892 Foreign government bonds 32 — — 32 167 — (1 ) 166 Mortgage-backed securities — — — — 8 — — 8 Total debt securities $ 2,084 $ 31 $ — $ 2,115 $ 7,340 $ 6 $ (85 ) $ 7,261 Publicly traded equity securities (1) 691 456 Total debt and publicly traded equity securities $ 2,806 $ 7,717 (1) Unrealized net losses (gains) recognized in Other (income) expense, net on equity securities still held at September 30, 2019 were $25 million and $(10) million , for the third quarter of 2019 and 2018 , respectively, and were $(41) million and $(60) million for the first nine months of 2019 and 2018 , respectively.
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	Financial assets and liabilities measured at fair value on a recurring basis are summarized below: Fair Value Measurements Using Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total ($ in millions) September 30, 2019 December 31, 2018 Assets Investments Corporate notes and bonds $ — $ 1,284 $ — $ 1,284 $ — $ 4,835 $ — $ 4,835 Asset-backed securities (1) — 437 — 437 — 1,253 — 1,253 U.S. government and agency securities — 301 — 301 — 731 — 731 Foreign government bonds — 32 — 32 — 166 — 166 Publicly traded equity securities 206 — — 206 147 — — 147 206 2,054 — 2,260 147 6,985 — 7,132 Other assets (2) U.S. government and agency securities 61 — — 61 55 106 — 161 Corporate notes and bonds — — — — — 85 — 85 Mortgage-backed securities — — — — — 8 — 8 Asset-backed securities (1) — — — — — 22 — 22 Publicly traded equity securities 485 — — 485 309 — — 309 546 — — 546 364 221 — 585 Derivative assets (3) Forward exchange contracts — 259 — 259 — 241 — 241 Purchased currency options — 202 — 202 — 213 — 213 Interest rate swaps — 22 — 22 — — — — — 483 — 483 — 454 — 454 Total assets $ 752 $ 2,537 $ — $ 3,289 $ 511 $ 7,660 $ — $ 8,171 Liabilities Other liabilities Contingent consideration $ — $ — $ 755 $ 755 $ — $ — $ 788 $ 788 Derivative liabilities (3) Forward exchange contracts — 105 — 105 — 74 — 74 Interest rate swaps — 3 — 3 — 81 — 81 Written currency options — 2 — 2 — 5 — 5 — 110 — 110 — 160 — 160 Total liabilities $ — $ 110 $ 755 $ 865 $ — $ 160 $ 788 $ 948 (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: Nine Months Ended September 30, ($ in millions) 2019 2018 Fair value January 1 $ 788 $ 935 Changes in estimated fair value (1) 52 144 Additions — 8 Payments (85 ) (235 ) Fair value September 30 (2) $ 755 $ 852 (1) Recorded in Cost of sales, Research and development expenses, and Other (income) expense, net . Includes cumulative translation adjustments. (2) Balance at September 30, 2019 includes $112 million recorded as a current liability for amounts expected to be paid within the next 12 months.

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 30, 2019
Inventory Disclosure [Abstract]
Schedule of Inventories	Inventories consisted of: ($ in millions) September 30, 2019 December 31, 2018 Finished goods $ 1,698 $ 1,658 Raw materials and work in process 5,526 5,004 Supplies 213 194 Total (approximates current cost) 7,437 6,856 (Decrease) increase to LIFO costs (67 ) 1 $ 7,370 $ 6,857 Recognized as: Inventories $ 5,855 $ 5,440 Other assets 1,515 1,417

Loans Payable, Long-Term Debt_2

Loans Payable, Long-Term Debt and Leases Loans Payable, Long-Term Debt and Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Loans Payable, Long-Term Debt and Leases [Abstract]
Supplemental Balance Sheet Information	Supplemental balance sheet information related to operating leases is as follows: ($ in millions) September 30, 2019 Assets Other Assets (1) $ 1,085 Liabilities Accrued and other current liabilities $ 241 Other Noncurrent Liabilities 779 $ 1,020 Weighted-average remaining lease term (years) 7.5 Weighted-average discount rate 3.3 % (1) Includes prepaid leases that have no related lease liability.
Schedule of Maturities of Operating Lease Liabilities	Maturities of operating leases liabilities are as follows: ($ in millions) September 30, 2019 2019 (excluding the nine months ended September 30, 2019) $ 71 2020 235 2021 189 2022 155 2023 127 Thereafter 374 Total lease payments 1,151 Less: imputed interest (131 ) $ 1,020

Equity (Tables)

Equity (Tables)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Equity	Three Months Ended September 30, Common Stock Other Paid-In Capital Retained Earnings Accumulated Other Comprehensive Loss Treasury Stock Non- controlling Interests Total ($ and shares in millions except per share amounts) Shares Par Value Shares Cost Balance at July 1, 2018 3,577 $ 1,788 $ 39,741 $ 41,523 $ (5,122 ) 907 $ (45,401 ) $ 237 $ 32,766 Net income attributable to Merck & Co., Inc. — — — 1,950 — — — — 1,950 Other comprehensive loss, net of taxes — — — — (29 ) — — — (29 ) Cash dividends declared on common stock ($0.48 per share) — — — (1,284 ) — — — — (1,284 ) Treasury stock shares purchased — — — — — 16 (996 ) — (996 ) Share-based compensation plans and other — — 21 — — (5 ) 231 — 252 Net income attributable to noncontrolling interests — — — — — — — 8 8 Distributions attributable to noncontrolling interests — — — — — — — (11 ) (11 ) Balance at September 30, 2018 3,577 $ 1,788 $ 39,762 $ 42,189 $ (5,151 ) 918 $ (46,166 ) $ 234 $ 32,656 Balance at July 1, 2019 3,577 $ 1,788 $ 39,484 $ 45,295 $ (5,362 ) 1,010 $ (53,570 ) $ 102 $ 27,737 Net income attributable to Merck & Co., Inc. — — — 1,901 — — — — 1,901 Other comprehensive loss, net of taxes — — — — (28 ) — — — (28 ) Cash dividends declared on common stock ($0.55 per share) — — — (1,392 ) — — — — (1,392 ) Treasury stock shares purchased — — — — — 17 (1,405 ) — (1,405 ) Share-based compensation plans and other — — 77 — — (1 ) 50 — 127 Net income attributable to noncontrolling interests — — — — — — — 6 6 Distributions attributable to noncontrolling interests — — — — — — — (21 ) (21 ) Balance at September 30, 2019 3,577 $ 1,788 $ 39,561 $ 45,804 $ (5,390 ) 1,026 $ (54,925 ) $ 87 $ 26,925 Nine Months Ended September 30, Common Stock Other Paid-In Capital Retained Earnings Accumulated Other Comprehensive Loss Treasury Stock Non- controlling Interests Total ($ and shares in millions except per share amounts) Shares Par Value Shares Cost Balance at January 1, 2018 3,577 $ 1,788 $ 39,902 $ 41,350 $ (4,910 ) 880 $ (43,794 ) $ 233 $ 34,569 Net income attributable to Merck & Co., Inc. — — — 4,393 — — — — 4,393 Adoption of new accounting standards — — — 322 (274 ) — — — 48 Other comprehensive income, net of taxes — — — — 33 — — — 33 Cash dividends declared on common stock ($1.44 per share) — — — (3,876 ) — — — — (3,876 ) Treasury stock shares purchased — — — — — 53 (3,158 ) — (3,158 ) Share-based compensation plans and other — — (140 ) — — (15 ) 786 — 646 Net income attributable to noncontrolling interests — — — — — — — 22 22 Distributions attributable to noncontrolling interests — — — — — — — (21 ) (21 ) Balance at September 30, 2018 3,577 $ 1,788 $ 39,762 $ 42,189 $ (5,151 ) 918 $ (46,166 ) $ 234 $ 32,656 Balance at January 1, 2019 3,577 $ 1,788 $ 38,808 $ 42,579 $ (5,545 ) 985 $ (50,929 ) $ 181 $ 26,882 Net income attributable to Merck & Co., Inc. — — — 7,487 — — — — 7,487 Other comprehensive income, net of taxes — — — — 155 — — — 155 Cash dividends declared on common stock ($1.65 per share) — — — (4,262 ) — — — — (4,262 ) Treasury stock shares purchased — — 1,000 — — 54 (4,730 ) — (3,730 ) Share-based compensation plans and other — — (247 ) — — (13 ) 734 — 487 Net loss attributable to noncontrolling interests — — — — — — — (73 ) (73 ) Distributions attributable to noncontrolling interests — — — — — — — (21 ) (21 ) Balance at September 30, 2019 3,577 $ 1,788 $ 39,561 $ 45,804 $ (5,390 ) 1,026 $ (54,925 ) $ 87 $ 26,925

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [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 Nine Months Ended ($ in millions) 2019 2018 2019 2018 Pretax share-based compensation expense $ 101 $ 91 $ 306 $ 261 Income tax benefit (14 ) (14 ) (42 ) (42 ) Total share-based compensation expense, net of taxes $ 87 $ 77 $ 264 $ 219
Assumptions Used to Determine Weighted-Average Fair Value of Options Granted	The weighted-average fair value of options granted during the first nine months of 2019 and 2018 was $10.63 and $8.19 per option, respectively, and was determined using the following assumptions: Nine Months Ended 2019 2018 Expected dividend yield 3.2 % 3.4 % Risk-free interest rate 2.4 % 2.8 % Expected volatility 18.7 % 19.1 % Expected life (years) 5.9 6.1

Pension and Other Postretirem_2

Pension and Other Postretirement Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2019
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 of such plans consisted of the following components: Three Months Ended Nine Months Ended 2019 2018 2019 2018 ($ in millions) U.S. International U.S. International U.S. International U.S. International Service cost $ 76 $ 58 $ 77 $ 56 $ 221 $ 178 $ 245 $ 181 Interest cost 115 44 109 43 343 133 324 134 Expected return on plan assets (202 ) (106 ) (209 ) (106 ) (613 ) (320 ) (634 ) (326 ) Amortization of unrecognized prior service credit (12 ) (3 ) (12 ) (3 ) (37 ) (9 ) (37 ) (10 ) Net loss amortization 43 16 63 21 113 47 174 64 Termination benefits 3 — 1 — 7 1 18 — Curtailments 5 — 3 — 6 — 7 (1 ) Settlements — — — — — — 1 3 $ 28 $ 9 $ 32 $ 11 $ 40 $ 30 $ 98 $ 45
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 credit of such plans consisted of the following components: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Service cost $ 12 $ 15 $ 36 $ 43 Interest cost 17 17 52 52 Expected return on plan assets (18 ) (21 ) (54 ) (63 ) Amortization of unrecognized prior service credit (20 ) (21 ) (59 ) (63 ) Net loss amortization (3 ) — (7 ) 1 Termination benefits 1 — 1 2 Curtailments (3 ) (1 ) (4 ) (7 ) $ (14 ) $ (11 ) $ (35 ) $ (35 )

Other (Income) Expense, Net (Ta

Other (Income) Expense, Net (Tables)	9 Months Ended
	Sep. 30, 2019
Other Income and Expenses [Abstract]
Other (Income) Expense, Net	Other (income) expense, net, consisted of: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Interest income $ (61 ) $ (92 ) $ (225 ) $ (257 ) Interest expense 231 190 674 569 Exchange losses 38 42 166 119 Income from investments in equity securities, net (1) (16 ) (198 ) (50 ) (376 ) Net periodic defined benefit plan (credit) cost other than service cost (128 ) (119 ) (409 ) (384 ) Other, net (29 ) 5 206 (183 ) $ 35 $ (172 ) $ 362 $ (512 ) (1) Includes net realized and unrealized gains and losses from investments in equity securities either owned directly or through ownership interests in investments funds.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Calculations of Earnings Per Share	The calculations of earnings per share are as follows: Three Months Ended Nine Months Ended ($ and shares in millions except per share amounts) 2019 2018 2019 2018 Net income attributable to Merck & Co., Inc. $ 1,901 $ 1,950 $ 7,487 $ 4,393 Average common shares outstanding 2,558 2,662 2,572 2,680 Common shares issuable (1) 14 16 15 14 Average common shares outstanding assuming dilution 2,572 2,678 2,587 2,694 Basic earnings per common share attributable to Merck & Co., Inc. common shareholders $ 0.74 $ 0.73 $ 2.91 $ 1.64 Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders $ 0.74 $ 0.73 $ 2.89 $ 1.63 (1) Issuable primarily under share-based compensation plans.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Changes in AOCI by Component	Changes in AOCI by component are as follows: Three Months Ended September 30, ($ in millions) Derivatives Investments Employee Benefit Plans Cumulative Translation Adjustment Accumulated Other Comprehensive Income (Loss) Balance July 1, 2018, net of taxes $ 65 $ (164 ) $ (3,065 ) $ (1,958 ) $ (5,122 ) Other comprehensive income (loss) before reclassification adjustments, pretax 29 8 — (147 ) (110 ) Tax (6 ) — — 11 5 Other comprehensive income (loss) before reclassification adjustments, net of taxes 23 8 — (136 ) (105 ) Reclassification adjustments, pretax 5 (1) 32 (2) 47 (3) — 84 Tax (1 ) — (7 ) — (8 ) Reclassification adjustments, net of taxes 4 32 40 — 76 Other comprehensive income (loss), net of taxes 27 40 40 (136 ) (29 ) Balance September 30, 2018, net of taxes $ 92 $ (124 ) $ (3,025 ) $ (2,094 ) $ (5,151 ) Balance July 1, 2019, net of taxes $ 66 $ 48 $ (3,530 ) $ (1,946 ) $ (5,362 ) Other comprehensive income (loss) before reclassification adjustments, pretax 186 8 (4 ) (84 ) 106 Tax (39 ) — — (33 ) (72 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes 147 8 (4 ) (117 ) 34 Reclassification adjustments, pretax (71 ) (1) (25 ) (2) 21 (3) — (75 ) Tax 15 — (2 ) — 13 Reclassification adjustments, net of taxes (56 ) (25 ) 19 — (62 ) Other comprehensive income (loss), net of taxes 91 (17 ) 15 (117 ) (28 ) Balance September 30, 2019, net of taxes $ 157 $ 31 $ (3,515 ) $ (2,063 ) $ (5,390 ) Nine Months Ended September 30, ($ in millions) Derivatives Investments Employee Benefit Plans Cumulative Translation Adjustment Accumulated Other Comprehensive Income (Loss) Balance January 1, 2018, net of taxes $ (108 ) $ (61 ) $ (2,787 ) $ (1,954 ) $ (4,910 ) Other comprehensive income (loss) before reclassification adjustments, pretax 113 (125 ) (2 ) (129 ) (143 ) Tax (24 ) 1 4 (111 ) (130 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes 89 (124 ) 2 (240 ) (273 ) Reclassification adjustments, pretax 169 (1) 68 (2) 128 (3) — 365 Tax (35 ) — (24 ) — (59 ) Reclassification adjustments, net of taxes 134 68 104 — 306 Other comprehensive income (loss), net of taxes 223 (56 ) 106 (240 ) 33 Adoption of ASU 2018-02 (23 ) 1 (344 ) 100 (266 ) Adoption of ASU 2016-01 — (8 ) — — (8 ) Balance September 30, 2018, net of taxes $ 92 $ (124 ) $ (3,025 ) $ (2,094 ) $ (5,151 ) Balance January 1, 2019, net of taxes $ 166 $ (78 ) $ (3,556 ) $ (2,077 ) $ (5,545 ) Other comprehensive income (loss) before reclassification adjustments, pretax 183 139 (5 ) 47 364 Tax (38 ) — 6 (33 ) (65 ) Other comprehensive income (loss) before reclassification adjustments, net of taxes 145 139 1 14 299 Reclassification adjustments, pretax (195 ) (1) (30 ) (2) 49 (3) — (176 ) Tax 41 — (9 ) — 32 Reclassification adjustments, net of taxes (154 ) (30 ) 40 — (144 ) Other comprehensive income (loss), net of taxes (9 ) 109 41 14 155 Balance September 30, 2019, net of taxes $ 157 $ 31 $ (3,515 ) $ (2,063 ) $ (5,390 ) (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 debt securities that were reclassified from AOCI to Other (income) expense, net . (3) Includes net amortization of prior service cost and actuarial gains and losses included in net periodic benefit cost (see Note 12).

Segment Reporting (Tables)

Segment Reporting (Tables)	9 Months Ended
	Sep. 30, 2019
Segment Reporting [Abstract]
Sales of Company's products	Sales of the Company’s products were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 ($ in millions) U.S. Int’l Total U.S. Int’l Total U.S. Int’l Total U.S. Int’l Total Pharmaceutical: Oncology Keytruda $ 1,743 $ 1,327 $ 3,070 $ 1,109 $ 780 $ 1,889 $ 4,525 $ 3,448 $ 7,973 $ 2,906 $ 2,114 $ 5,020 Emend 42 56 98 71 52 123 173 163 336 239 157 396 Alliance revenue - Lynparza 71 53 123 33 15 49 186 126 313 88 37 125 Alliance revenue - Lenvima 65 44 109 30 13 43 169 112 280 49 29 78 Vaccines Gardasil/Gardasil 9 761 558 1,320 740 308 1,048 1,579 1,464 3,044 1,422 894 2,317 ProQuad/M-M-R II /Varivax 482 141 623 429 96 525 1,325 469 1,794 1,097 246 1,343 Pneumovax 23 179 58 237 160 54 214 428 164 592 394 192 586 RotaTeq 102 78 180 134 57 191 360 203 564 384 156 540 Vaqta 36 26 62 36 30 66 103 65 167 95 72 167 Hospital Acute Care Bridion 133 151 284 96 120 217 381 437 817 272 389 661 Noxafil 77 100 177 89 99 188 268 291 560 257 294 551 Cubicin 14 38 52 55 40 95 78 129 207 150 137 287 Primaxin 2 75 77 1 71 72 2 204 207 6 206 212 Invanz (1 ) 58 57 74 62 137 30 176 206 252 185 437 Cancidas — 62 62 2 77 79 5 187 191 10 247 257 Immunology Simponi — 203 203 — 210 210 — 625 625 — 673 673 Remicade — 101 101 — 135 135 — 322 322 — 459 459 Neuroscience Belsomra 23 57 80 23 43 66 68 155 223 76 115 191 Virology Isentress/Isentress HD 102 149 250 123 151 275 304 449 752 383 477 860 Zepatier 24 59 83 18 86 104 96 208 304 8 339 347 Cardiovascular Zetia 5 142 147 9 157 165 11 432 443 34 662 696 Vytorin 5 52 57 — 92 92 11 219 231 11 402 414 Atozet — 97 97 — 84 84 — 283 283 — 258 258 Adempas — 107 107 — 94 94 — 302 302 — 238 238 Diabetes Januvia 367 440 807 498 429 927 1,223 1,317 2,539 1,466 1,291 2,756 Janumet 129 375 503 225 339 563 462 1,105 1,567 625 1,067 1,693 Women’s Health NuvaRing 202 39 241 193 41 234 593 107 700 550 135 686 Implanon/Nexplanon 136 62 199 133 53 186 421 160 581 375 160 535 Diversified Brands Singulair 11 140 152 5 156 161 24 479 503 16 505 521 Cozaar/Hyzaar 6 110 116 4 99 103 16 313 329 18 330 348 Nasonex 4 55 58 7 64 71 2 224 226 8 266 274 Arcoxia — 72 72 — 83 83 — 221 221 — 249 249 Follistim AQ 27 35 62 26 34 60 80 102 182 83 115 198 Other pharmaceutical (1) 385 842 1,229 326 786 1,109 1,142 2,492 3,634 932 2,557 3,486 Total Pharmaceutical segment sales 5,132 5,962 11,095 4,649 5,010 9,658 14,065 17,153 31,218 12,206 15,653 27,859 Animal Health: Livestock 144 582 726 153 508 660 406 1,601 2,007 383 1,563 1,946 Companion Animals 193 203 396 153 207 361 560 704 1,264 541 689 1,230 Total Animal Health segment sales 337 785 1,122 306 715 1,021 966 2,305 3,271 924 2,252 3,176 Other segment sales (2) 46 — 46 55 — 55 133 1 133 194 1 195 Total segment sales 5,515 6,747 12,263 5,010 5,725 10,734 15,164 19,459 34,622 13,324 17,906 31,230 Other (3) 10 125 134 20 39 60 19 330 350 101 (35 ) 66 $ 5,525 $ 6,872 $ 12,397 $ 5,030 $ 5,764 $ 10,794 $ 15,183 $ 19,789 $ 34,972 $ 13,425 $ 17,871 $ 31,296 U.S. plus international may not equal total due to rounding . (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.
Consolidated revenues by geographic area	Consolidated sales by geographic area where derived are as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 United States $ 5,525 $ 5,030 $ 15,183 $ 13,425 Europe, Middle East and Africa 3,189 2,884 9,452 9,218 Japan 919 761 2,639 2,353 China 914 512 2,423 1,556 Asia Pacific (other than Japan and China) 756 666 2,217 2,210 Latin America 671 622 1,889 1,748 Other 423 319 1,169 786 $ 12,397 $ 10,794 $ 34,972 $ 31,296
Reconciliation of segment profits to income before taxes	A reconciliation of segment profits to Income before taxes is as follows: Three Months Ended Nine Months Ended ($ in millions) 2019 2018 2019 2018 Segment profits: Pharmaceutical segment $ 7,747 $ 6,621 $ 21,437 $ 18,535 Animal Health segment 423 409 1,243 1,273 Other segments (2 ) 5 (2 ) 94 Total segment profits 8,168 7,035 22,678 19,902 Other profits (losses) 101 55 226 (35 ) Unallocated: Interest income 61 92 225 257 Interest expense (231 ) (190 ) (674 ) (569 ) Depreciation and amortization (382 ) (324 ) (1,169 ) (1,006 ) Research and development (3,110 ) (1,997 ) (7,045 ) (7,304 ) Amortization of purchase accounting adjustments (329 ) (679 ) (1,105 ) (2,144 ) Restructuring costs (232 ) (171 ) (444 ) (494 ) Charge related to termination of collaboration agreement with Samsung — (420 ) — (420 ) Other unallocated, net (1,699 ) (736 ) (4,019 ) (2,090 ) $ 2,347 $ 2,665 $ 8,673 $ 6,097

Basis of Presentation (Details)

Basis of Presentation (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating leases, right of use asset	$ 1,085
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating leases, right of use asset		$ 1,100

Acquisitions, Divestitures, R_3

Acquisitions, Divestitures, Research Collaborations and License Agreements - Acquisitions (Details) $ in Millions, $ in Millions	Apr. 01, 2019USD ($)	Jul. 31, 2019USD ($)	Apr. 30, 2019USD ($)	Jun. 30, 2018AUD ($)	Jun. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Goodwill						$ 19,480		$ 19,480		$ 18,253
Research and development						3,204	$ 2,068	7,324	$ 7,538
Peloton
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Payment to acquire business		$ 1,200
Other assets and liabilities, net		6
Cash and cash equivalents		157
Deferred income tax liabilities		64
Research and development						$ 982		$ 982
Antelliq
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Payment to acquire business	$ 2,300
Other assets and liabilities, net	81
Payment of debt	1,300
Transaction costs	47
Cash and cash equivalents	31
Deferred income tax liabilities	563
Goodwill	$ 1,345
Immune Design
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Payment to acquire business			$ 301
Intangible assets recognized			156
Cash and cash equivalents			83
Other assets recognized			31
Goodwill			$ 31
Viralytics
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Payment to acquire business				$ 502	$ 378
Other assets recognized					$ 34
Research and development									$ 344
Sales-Based Milestones | Peloton
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Potential future milestone payments, maximum		1,050
Commercial Milestones | Peloton
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Potential future milestone payments, maximum		50
Regulatory Milestones | Peloton
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Potential future milestone payments, maximum		$ 50

Acquisitions, Divestitures, R_4

Acquisitions, Divestitures, Research Collaborations and License Agreements - Fair Value of Assets Acquired and Liabilities Assumed (Details) $ in Millions	Apr. 01, 2019USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Goodwill		$ 19,480	$ 18,253
Antelliq
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Cash and cash equivalents	$ 31
Accounts receivable	73
Inventories	95
Property, plant and equipment	62
Identifiable intangible assets (useful lives ranging from 18-24 years)	2,689
Deferred income tax liabilities	(563)
Other assets and liabilities, net	(81)
Total identifiable net assets	2,306
Goodwill	1,345
Consideration transferred	$ 3,651
Measurement Input, Discount Rate | Antelliq
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Present value discount rate	0.115
Minimum | Antelliq
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Useful lives of identifiable intangible assets	18 years
Maximum | Antelliq
Acquisitions Research Collaborations And License Agreements Transactions [Line Items]
Useful lives of identifiable intangible assets	24 years

Acquisitions, Divestitures, R_5

Acquisitions, Divestitures, Research Collaborations and License Agreements - Divestitures (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Charge related to termination of collaboration agreement with Samsung		$ 0	$ (420)
Samsung
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Charge related to termination of collaboration agreement with Samsung	$ (420)
Contract termination fee	155
Inventory write-off related to contract termination	137
Fixed asset abandonment costs related to contract termination	122
Other contract termination costs	$ 6

Collaborative Arrangements - Na

Collaborative Arrangements - Narrative (Details) - USD ($) $ in Millions

1 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

18 Months Ended

37 Months Ended

Mar. 31, 2021

Mar. 31, 2020

Dec. 31, 2019

Jun. 30, 2019

Apr. 30, 2019

Mar. 31, 2019

Dec. 31, 2018

Mar. 31, 2018

Dec. 31, 2017

Jul. 31, 2017

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Sep. 30, 2018

Mar. 31, 2018

Sep. 30, 2019

Sep. 30, 2018

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2018

Mar. 31, 2021

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Research and development

$ 3,204

$ 2,068

$ 7,324

$ 7,538

Other liabilities, noncurrent

$ 12,041

11,085

11,085

$ 12,041

$ 12,041

Lynparza | Other Assets

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Finite-lived intangible assets

983

983

Lenvima | Other Assets

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Finite-lived intangible assets

664

664

Adempas | Other intangible assets

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Finite-lived intangible assets

$ 893

893

AstraZeneca

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Upfront and milestone payments

$ 1,600

License option payment related to collaborative arrangement

$ 400

$ 250

$ 750

Research and development

$ 2,350

AstraZeneca | Forecast

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

License option payment related to collaborative arrangement

$ 100

AstraZeneca | Lynparza

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Cumulative amortization expense

$ 52

AstraZeneca | Sales-Based Milestones

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Probable contingent payments collaborative arrangement

$ 700

Contingent milestone payments collaborative arrangement

3,100

AstraZeneca | Sales-Based Milestones | Lynparza

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Probable contingent payments collaborative arrangement

300

Liabilities

$ 300

$ 300

Milestone payments made to collaborative partner

450

AstraZeneca | Regulatory Milestones | Lynparza

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payments made to collaborative partner

$ 30

$ 30

140

Contingent milestone payments collaborative arrangement

1,700

Eisai

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Upfront and milestone payments

$ 750

License option payment related to collaborative arrangement

$ 325

Research and development

$ 1,400

Eisai | Forecast

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

License option payment related to collaborative arrangement

$ 125

$ 200

$ 650

Eisai | Lenvima

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Cumulative amortization expense

$ 35

Eisai | Sales-Based Milestones

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Contingent milestone payments collaborative arrangement

3,970

3,420

Eisai | Sales-Based Milestones | Lenvima

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Probable contingent payments collaborative arrangement

282

268

Liabilities

$ 282

$ 282

Milestone payments made to collaborative partner

50

Eisai | Regulatory Milestones

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Contingent milestone payments collaborative arrangement

385

135

Eisai | Regulatory Milestones | Lenvima

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payments made to collaborative partner

$ 250

Bayer AG | Adempas

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Cumulative amortization expense

106

Bayer AG | Sales-Based Milestones

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Probable contingent payments collaborative arrangement

375

Milestone payments made to collaborative partner

350

Contingent milestone payments collaborative arrangement

$ 400

Other liabilities, noncurrent

$ 375

$ 375

Collaborative Arrangements - Sc

Collaborative Arrangements - Schedule of Transactions (Details) - Collaborative Arrangement - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Other current assets | AstraZeneca
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Receivables from counterparty	$ 119		$ 119		$ 52
Other current assets | Eisai
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Receivables from counterparty	109		109		71
Other current assets | Bayer AG
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Receivables from counterparty	44		44		32
Accounts payable and accrued liabilities | AstraZeneca
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payables to counterparty	578		578		405
Accounts payable and accrued liabilities | Eisai
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payables to counterparty	692		692		375
Other Noncurrent Liabilities | AstraZeneca
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payables to counterparty	300		300		250
Other Noncurrent Liabilities | Eisai
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payables to counterparty	125		125		543
Other Noncurrent Liabilities | Bayer AG
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payables to counterparty	375		375		$ 375
Revenue | AstraZeneca
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total sales	123	$ 49	313	$ 125
Revenue | Eisai
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total sales	109	43	280	78
Revenue | Bayer AG
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Net product sales recorded by Merck	57	47	158	138
Merck’s profit share from sales in Bayer’s marketing territories	50	47	144	100
Total sales	107	94	302	238
Cost of sales | AstraZeneca
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expenses	28	12	120	48
Cost of sales | Eisai
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expenses	23	8	97	9
Cost of sales | Bayer AG
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expenses	28	29	86	188
Selling, general and administrative | AstraZeneca
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expenses	36	12	96	28
Selling, general and administrative | Eisai
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expenses	21	5	59	7
Selling, general and administrative | Bayer AG
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expenses	12	11	31	26
Research and development | AstraZeneca
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expenses	44	47	122	118
Research and development | Eisai
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expenses	37	36	146	1,473
Research and development | Bayer AG
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expenses	$ 31	$ 34	$ 94	$ 90

Restructuring - Narrative (Deta

Restructuring - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Estimate of cumulative pre tax costs that will result in cash outlays			60.00%
Estimate of cumulative pre tax costs that will be noncash			40.00%
Expected restructuring and related cost	$ 750		$ 750
Total pretax restructuring costs	296	$ 169	642	$ 508
Minimum
Restructuring Cost and Reserve [Line Items]
Expected restructuring and related cost	800		800
Maximum
Restructuring Cost and Reserve [Line Items]
Expected restructuring and related cost	$ 1,200		$ 1,200

Restructuring - Charges Activit

Restructuring - Charges Activities by Type of Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	$ 296	$ 169	$ 642	$ 508
Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	205	137	358	392
Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	41	(8)	173	(10)
Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	50	40	111	126
Cost of sales
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	62	2	161	11
Cost of sales | Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	0	0	0
Cost of sales | Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	41	1	139	1
Cost of sales | Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	21	1	22	10
Selling, general and administrative
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	1	0	33	2
Selling, general and administrative | Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	0	0	0
Selling, general and administrative | Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	1	0	33	1
Selling, general and administrative | Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	0	0	1
Research and development
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	1	(4)	4	1
Research and development | Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	0	0	0
Research and development | Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	(1)	(9)	1	(12)
Research and development | Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	2	5	3	13
Restructuring costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	232	171	444	494
Restructuring costs | Separation Costs
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	205	137	358	392
Restructuring costs | Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	0	0	0	0
Restructuring costs | Other
Restructuring Cost and Reserve [Line Items]
Total pretax restructuring costs	$ 27	$ 34	$ 86	$ 102

Restructuring - Activities by P

Restructuring - Activities by Program (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance			$ 534
Expense	$ 296	$ 169	642	$ 508
(Payments) receipts, net			(356)
Non-cash activity			(153)
Restructuring reserve, ending balance	667		667
Separation Costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance			443
Expense	205	137	358	392
(Payments) receipts, net			(198)
Non-cash activity			0
Restructuring reserve, ending balance	603		603
Accelerated Depreciation
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance			0
Expense	41	(8)	173	(10)
(Payments) receipts, net			0
Non-cash activity			(173)
Restructuring reserve, ending balance	0		0
Other
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance			91
Expense	50	$ 40	111	$ 126
(Payments) receipts, net			(158)
Non-cash activity			20
Restructuring reserve, ending balance	$ 64		$ 64

Financial Instruments - Narrati

Financial Instruments - Narrative (Details)	9 Months Ended
	Sep. 30, 2019USD ($)interest_rate_swap	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Derivative [Line Items]
Number of interest rate swaps held (in interest rate swaps) | interest_rate_swap	19
Pretax net unrealized gain on derivatives maturing within next 12 months estimated to be reclassified from AOCI to sales	$ 174,000,000
Equity investments without readily determinable fair values	393,000,000
Unrealized gains recognized on investments in equity securities without readily determinable fair values	4,000,000
Unrealized losses recognized on investments in equity securities without readily determinable fair values	12,000,000
Cumulative unrealized gains on investments	172,000,000
Cumulative unrealized losses on investments	21,000,000
Available-for-sale debt securities included in Short-term investments	129,000,000
Available-for-sale debt securities maturing after one year through five years	1,800,000,000
Cash and cash equivalents	7,869,000,000		$ 7,965,000,000
Payments of contingent consideration	85,000,000	$ 235,000,000
Fair value of loans payable and long-term debt, including current portion	28,700,000,000		25,600,000,000
Debt, carrying amount	26,100,000,000		25,100,000,000
Cash collateral received from counterparties	133,000,000		107,000,000
Cash collateral advanced to counterparties	0		$ 0
Significant Other Observable Inputs (Level 2)
Derivative [Line Items]
Cash and cash equivalents	7,900,000,000
Cash equivalents	$ 7,100,000,000
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
gefapixant
Derivative [Line Items]
Payments of contingent consideration		$ 175,000,000

Financial Instruments - Effect

Financial Instruments - Effect of Net Investment Hedges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income	$ 1	$ (10)	$ 8	$ (24)
Foreign exchange contracts | Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing	(8)	(4)	(23)	(7)
Euro-denominated notes
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income	(150)	38	(152)	(54)
Euro-denominated notes | Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing	$ 0	$ 0	$ 0	$ 0

Financial Instruments - Summary

Financial Instruments - Summary of Interest Rate Swaps Held (Details)	Sep. 30, 2019USD ($)interest_rate_swap	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Derivative [Line Items]
Par Value of Debt		$ 5,000,000,000
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap	19
Total Swap Notional Amount	$ 28,359,000,000		$ 29,742,000,000
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	Sep. 30, 2019	Dec. 31, 2018
Loans payable and current portion of long-term debt
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Liabilities	$ 1,247	$ 0
Cumulative Amount of Fair Value Hedging Adjustment Increase (Decrease) Included in the Carrying Amount	(3)	0
Long-Term Debt
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Liabilities	3,416	4,560
Cumulative Amount of Fair Value Hedging Adjustment Increase (Decrease) Included in the Carrying Amount	$ 22	$ (82)

Financial Instruments - Fair _2

Financial Instruments - Fair Value of Derivatives Segregated between those Derivatives that are Designated as Hedging Instruments and those that are Not Designated as Hedging Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	$ 483	$ 454
Fair Value of Derivative, Liability	110	160
U.S Dollar Notional Amount	28,359	29,742
Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	330	338
Fair Value of Derivative, Liability	10	89
U.S Dollar Notional Amount	14,651	14,390
Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	153	116
Fair Value of Derivative, Liability	100	71
U.S Dollar Notional Amount	13,708	15,352
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Other Assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	22	0
U.S Dollar Notional Amount	3,400	0
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Accrued and other current liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	3	0
U.S Dollar Notional Amount	1,250	0
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	0	81
U.S Dollar Notional Amount	0	4,650
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other Assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	56	75
U.S Dollar Notional Amount	2,073	2,655
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Accrued and other current liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	6	7
U.S Dollar Notional Amount	775	774
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 Amount	9	89
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other current assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	252	263
U.S Dollar Notional Amount	7,144	6,222
Foreign exchange contracts | Derivatives Not Designated as Hedging Instruments | Accrued and other current liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	100	71
U.S Dollar Notional Amount	6,906	9,922
Foreign exchange contracts | Derivatives Not Designated as Hedging Instruments | Other current assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	153	116
U.S Dollar Notional Amount	$ 6,802	$ 5,430

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 ($)	Sep. 30, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross amounts recognized in the consolidated balance sheet, asset	$ 483,000,000	$ 454,000,000
Gross amount subject to offset in master netting arrangements not offset in the condensed balance sheet, asset	(73,000,000)	(121,000,000)
Cash collateral received, asset	(133,000,000)	(107,000,000)
Net amounts, asset	277,000,000	226,000,000
Gross amounts recognized in the consolidated balance sheet, liability	110,000,000	160,000,000
Gross amount subject to offset in master netting arrangements not offset in the condensed balance sheet, liability	(73,000,000)	(121,000,000)
Cash collateral received, liability	0	0
Net amounts, liability	$ 37,000,000	$ 39,000,000

Financial Instruments - Locatio

Financial Instruments - Location and Amount of Pretax (Gains) Losses of Derivatives (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Sales	$ 12,397	$ 10,794	$ 34,972	$ 31,296
Other (income) expense, net	35	(172)	362	(512)
Other comprehensive income (loss)	(28)	(29)	155	33
Interest rate swap contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (loss) recognized in OCI on derivatives	(1)	(1)	(6)	(3)
Interest rate swap contracts | Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items	13	(9)	101	(86)
Derivatives designated as hedging instruments	(6)	15	(74)	100
Amount of gain recognized in Other (income) expense, net on derivatives	(1)	(1)	(3)	(3)
Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (loss) recognized in OCI on derivatives	186	29	183	113
Increase (decrease) in Sales as a result of AOCI reclassifications	(70)	6	(189)	172
Foreign exchange contracts | Reclassification out of Accumulated Other Comprehensive Income | Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest
Derivative Instruments, Gain (Loss) [Line Items]
Sales	$ 70	$ (6)	$ 189	$ (172)

Financial Instruments - Income

Financial Instruments - Income Statement Effects on Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Foreign currency | Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Pretax (Gain) Loss Recognized in Income	$ (8)	$ (57)	$ 112	$ (224)
Forecasted transactions | Sales
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Pretax (Gain) Loss Recognized in Income	$ (11)	$ 0	$ (7)	$ (5)

Financial Instruments - Infor_2

Financial Instruments - Information on Available-for-sale Investments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	$ 2,084		$ 2,084		$ 7,340
Debt securities, unrealized gains	31		31		6
Debt securities, unrealized losses	0		0		(85)
Debt securities, fair value	2,115		2,115		7,261
Publicly traded equity securities, fair value	691		691		456
Total debt and publicly traded equity securities, fair value	2,806		2,806		7,717
Unrealized net losses (gains)	25	$ (10)	(41)	$ (60)
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	1,260		1,260		4,985
Debt securities, unrealized gains	24		24		3
Debt securities, unrealized losses	0		0		(68)
Debt securities, fair value	1,284		1,284		4,920
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	434		434		1,285
Debt securities, unrealized gains	3		3		1
Debt securities, unrealized losses	0		0		(11)
Debt securities, fair value	437		437		1,275
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	358		358		895
Debt securities, unrealized gains	4		4		2
Debt securities, unrealized losses	0		0		(5)
Debt securities, fair value	362		362		892
Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	32		32		167
Debt securities, unrealized gains	0		0		0
Debt securities, unrealized losses	0		0		(1)
Debt securities, fair value	32		32		166
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	0		0		8
Debt securities, unrealized gains	0		0		0
Debt securities, unrealized losses	0		0		0
Debt securities, fair value	$ 0		$ 0		$ 8

Financial Instruments - Financi

Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Assets
Investments	$ 2,115	$ 7,261
Publicly traded equity securities	691	456
Derivative assets	483	454
Liabilities
Contingent consideration	755	788	$ 852	$ 935
Derivative liabilities	110	160
Corporate notes and bonds
Assets
Investments	1,284	4,920
Asset-backed securities
Assets
Investments	$ 437	1,275
Liabilities
Primary weighted average life of collateral	5 years
U.S. government and agency securities
Assets
Investments	$ 362	892
Mortgage-backed securities
Assets
Investments	0	8
Foreign government bonds
Assets
Investments	32	166
Fair Value, Measurements, Recurring
Assets
Investments	2,260	7,132
Other assets	546	585
Derivative assets	483	454
Total assets	3,289	8,171
Liabilities
Contingent consideration	755	788
Derivative liabilities	110	160
Total liabilities	865	948
Fair Value, Measurements, Recurring | Foreign exchange contracts
Assets
Derivative assets	259	241
Liabilities
Derivative liabilities	105	74
Fair Value, Measurements, Recurring | Interest rate swap contracts
Assets
Derivative assets	22	0
Fair Value, Measurements, Recurring | Currency options
Assets
Derivative assets	202	213
Liabilities
Derivative liabilities	2	5
Fair Value, Measurements, Recurring | Interest rate swap contracts
Liabilities
Derivative liabilities	3	81
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Investments	206	147
Other assets	546	364
Derivative assets	0	0
Total assets	752	511
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) | 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
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | 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) | Interest rate swap contracts
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets
Investments	2,054	6,985
Other assets	0	221
Derivative assets	483	454
Total assets	2,537	7,660
Liabilities
Contingent consideration	0	0
Derivative liabilities	110	160
Total liabilities	110	160
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign exchange contracts
Assets
Derivative assets	259	241
Liabilities
Derivative liabilities	105	74
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swap contracts
Assets
Derivative assets	22	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Currency options
Assets
Derivative assets	202	213
Liabilities
Derivative liabilities	2	5
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swap contracts
Liabilities
Derivative liabilities	3	81
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	755	788
Derivative liabilities	0	0
Total liabilities	755	788
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
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Currency options
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Interest rate swap contracts
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Corporate notes and bonds
Assets
Investments	1,284	4,835
Other assets	0	85
Fair Value, Measurements, Recurring | Corporate notes and bonds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Corporate notes and bonds | Significant Other Observable Inputs (Level 2)
Assets
Investments	1,284	4,835
Other assets	0	85
Fair Value, Measurements, Recurring | Corporate notes and bonds | Significant Unobservable Inputs (Level 3)
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Asset-backed securities
Assets
Investments	437	1,253
Other assets	0	22
Fair Value, Measurements, Recurring | Asset-backed securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Asset-backed securities | Significant Other Observable Inputs (Level 2)
Assets
Investments	437	1,253
Other assets	0	22
Fair Value, Measurements, Recurring | Asset-backed securities | Significant Unobservable Inputs (Level 3)
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | U.S. government and agency securities
Assets
Investments	301	731
Other assets	61	161
Fair Value, Measurements, Recurring | U.S. government and agency securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Investments	0	0
Other assets	61	55
Fair Value, Measurements, Recurring | U.S. government and agency securities | Significant Other Observable Inputs (Level 2)
Assets
Investments	301	731
Other assets	0	106
Fair Value, Measurements, Recurring | U.S. government and agency securities | Significant Unobservable Inputs (Level 3)
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Mortgage-backed securities
Assets
Other assets	0	8
Fair Value, Measurements, Recurring | Mortgage-backed securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Assets
Other assets	0	8
Fair Value, Measurements, Recurring | Mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Assets
Other assets	0	0
Fair Value, Measurements, Recurring | Foreign government bonds
Assets
Investments	32	166
Fair Value, Measurements, Recurring | Foreign government bonds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Foreign government bonds | Significant Other Observable Inputs (Level 2)
Assets
Investments	32	166
Fair Value, Measurements, Recurring | Foreign government bonds | Significant Unobservable Inputs (Level 3)
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Publicly traded equity securities
Assets
Publicly traded equity securities	206	147
Other assets	485	309
Fair Value, Measurements, Recurring | Publicly traded equity securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Publicly traded equity securities	206	147
Other assets	485	309
Fair Value, Measurements, Recurring | Publicly traded equity securities | Significant Other Observable Inputs (Level 2)
Assets
Publicly traded equity securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Publicly traded equity securities | Significant Unobservable Inputs (Level 3)
Assets
Publicly traded equity securities	0	0
Other assets	$ 0	$ 0

Financial Instruments - Infor_3

Financial Instruments - Information About Changes in Liabilities for Contingent Consideration (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 788	$ 935
Changes in estimated fair value	52	144
Additions	0	8
Payments	(85)	(235)
Fair value, ending balance	755	$ 852
Current liability	$ 112

Inventories - Inventories (Deta

Inventories - Inventories (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Finished goods	$ 1,698	$ 1,658
Raw materials and work in process	5,526	5,004
Supplies	213	194
Total (approximates current cost)	7,437	6,856
(Decrease) increase to LIFO costs	(67)	1
Total current and noncurrent inventories	7,370	6,857
Recognized as:
Inventories	5,855	5,440
Other assets	$ 1,515	$ 1,417

Inventories - Narrative (Detail

Inventories - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Inventory [Line Items]
Inventories classified in Other assets	$ 1,515	$ 1,417
Inventories Not Expected to be Sold Within One Year
Inventory [Line Items]
Inventories classified in Other assets	1,400	1,400
Inventories Produced in Preparation for Product Launches
Inventory [Line Items]
Inventories classified in Other assets	$ 138	$ 7

Other Intangibles (Details)

Other Intangibles (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Intangible asset impairment charges	$ 612	$ 693
Intangible assets	12,307	12,307	$ 11,431
Sivextro
Finite-Lived Intangible Assets [Line Items]
Intangible asset impairment charges		612
Intangible assets	$ 175	$ 175

Loans Payable, Long-Term Debt_3

Loans Payable, Long-Term Debt and Leases - Debt Narrative (Details)	1 Months Ended
	Mar. 31, 2019USD ($)
Debt Instrument [Line Items]
Face amount of debt	$ 5,000,000,000
Net proceeds from offering	5,000,000,000
2.90% Notes Due 2024
Debt Instrument [Line Items]
Face amount of debt	$ 750,000,000
Stated interest rate (as percent)	2.90%
3.40% Notes Due 2029
Debt Instrument [Line Items]
Face amount of debt	$ 1,750,000,000
Stated interest rate (as percent)	3.40%
3.90% Notes Due 2039
Debt Instrument [Line Items]
Face amount of debt	$ 1,000,000,000
Stated interest rate (as percent)	3.90%
4.00% Notes Due 2049
Debt Instrument [Line Items]
Face amount of debt	$ 1,500,000,000
Stated interest rate (as percent)	4.00%

Loans Payable, Long-Term Debt_4

Loans Payable, Long-Term Debt and Leases Loans Payable, Long-Term Debt and Leases - Operating Leases (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Apr. 30, 2020	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term (in years)	7 years 6 months	7 years 6 months
Operating lease cost	$ 79	$ 244
Cash payments included in the measurement of operating lease liabilities	71	209
Obligations associated with operating leases not yet commenced	$ 444	$ 444
Due 2019				$ 188
Due 2020				198
Due 2021				150
Due 2022				134
Due 2023				84
Due thereafter				$ 243
Facilities
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term (in years)	8 years	8 years
Renewal term (in years)	4 years	4 years
Vehicle
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term (in years)	4 years	4 years
Forecast
Lessee, Lease, Description [Line Items]
Obligations associated with operating leases not yet commenced			$ 221
Lease not yet commenced, term of lease			10 years

Loans Payable, Long-Term Debt_5

Loans Payable, Long-Term Debt and Leases - Balance Sheet Information (Details) $ in Millions	Sep. 30, 2019USD ($)
Loans Payable, Long-Term Debt and Leases [Abstract]
Other Assets	$ 1,085
Accrued and other current liabilities	241
Other Noncurrent Liabilities	779
Operating lease liability	$ 1,020
Weighted-average remaining lease term (in years)	7 years 6 months
Weighted-average discount rate (as percent)	3.30%

Loans Payable, Long-Term Debt_6

Loans Payable, Long-Term Debt and Leases Loans Payable, Long-Term Debt and Leases - Maturity Schedule (Details) $ in Millions	Sep. 30, 2019USD ($)
Loans Payable, Long-Term Debt and Leases [Abstract]
2019 (excluding the nine months ended September 30, 2019)	$ 71
2020	235
2021	189
2022	155
2023	127
Thereafter	374
Total lease payments	1,151
Less: imputed interest	(131)
Operating lease liability	$ 1,020

Contingencies - Narrative (Deta

Contingencies - Narrative (Details) $ in Millions	1 Months Ended	9 Months Ended
	Mar. 31, 2014Case	Sep. 30, 2019USD ($)ClaimCase	Dec. 31, 2018USD ($)
Legal Defense Costs
Loss Contingencies [Line Items]
Legal defense costs reserve | $		$ 260	$ 245
Fosamax
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		3,900
Fosamax | Femur Fracture Litigation | Federal
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		11
Loss contingency, claims dismissed, number (in legal matters)	650	1,060
Loss contingency, claims on appeal, number (in legal matters)	515
Fosamax | Femur Fracture Litigation | New Jersey state court
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		2,520
Fosamax | Femur Fracture Litigation | California state court
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		275
Fosamax | Femur Fracture Litigation | Other state courts
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters)		4
Januvia
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters) | Claim		1,370
Januvia | Other state courts
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters) | Claim		6
Januvia | Cases Company Agreed To Toll Statute Of Limitations
Loss Contingencies [Line Items]
Loss contingency, pending claims, number (in legal matters) | Claim		50

Equity - Rollforward Reconcilia

Equity - Rollforward Reconciliations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Jan. 01, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, beginning balance (in shares)			3,577,103,522
Equity, beginning balance	$ 27,737	$ 32,766	$ 26,882	$ 34,569	$ 32,656
Net income attributable to Merck & Co., Inc.	1,901	1,950	7,487	4,393
Adoption of new accounting standards						$ 48
Other comprehensive income (loss), net of taxes	(28)	(29)	155	33
Cash dividends declared on common stock	(1,392)	(1,284)	(4,262)	(3,876)
Treasury stock shares purchased	(1,405)	(996)	(3,730)	(3,158)
Share-based compensation plans and other	127	252	487	646
Net income (loss) attributable to noncontrolling interests	6	8	(73)	22
Distributions attributable to noncontrolling interests	$ (21)	(11)	$ (21)	(21)
Shares, ending balance (in shares)	3,577,103,522		3,577,103,522		3,577,103,522
Equity, ending balance	$ 26,925	$ 32,656	$ 26,925	$ 32,656	$ 26,925
Cash dividends declared on common stock (in dollars per share)	$ 0.55	$ 0.48	$ 1.65	$ 1.44
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, beginning balance (in shares)	3,577,000,000	3,577,000,000	3,577,000,000	3,577,000,000	3,577,000,000
Equity, beginning balance	$ 1,788	$ 1,788	$ 1,788	$ 1,788	$ 1,788
Shares, ending balance (in shares)	3,577,000,000	3,577,000,000	3,577,000,000	3,577,000,000	3,577,000,000
Equity, ending balance	$ 1,788	$ 1,788	$ 1,788	$ 1,788	$ 1,788
Other Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	39,484	39,741	38,808	39,902	39,762
Treasury stock shares purchased	0		1,000
Share-based compensation plans and other	77	21	(247)	(140)
Equity, ending balance	39,561	39,762	39,561	39,762	39,561
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	45,295	41,523	42,579	41,350	42,189
Net income attributable to Merck & Co., Inc.	1,901	1,950	7,487	4,393
Adoption of new accounting standards						322
Cash dividends declared on common stock	(1,392)	(1,284)	(4,262)	(3,876)
Equity, ending balance	45,804	42,189	45,804	42,189	45,804
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	(5,362)	(5,122)	(5,545)	(4,910)	(5,151)
Adoption of new accounting standards						$ (274)
Other comprehensive income (loss), net of taxes	(28)	(29)	155	33
Equity, ending balance	$ (5,390)	$ (5,151)	$ (5,390)	$ (5,151)	$ (5,390)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, beginning balance (in shares)	1,010,000,000	907,000,000	985,000,000	880,000,000	918,000,000
Equity, beginning balance	$ (53,570)	$ (45,401)	$ (50,929)	$ (43,794)	$ (46,166)
Treasury stock shares purchased (in shares)	17,000,000	16,000,000	54,000,000	53,000,000
Treasury stock shares purchased	$ (1,405)	$ (996)	$ (4,730)	$ (3,158)
Share-based compensation plans and other (in shares)	(1,000,000)	(5,000,000)	(13,000,000)	(15,000,000)
Share-based compensation plans and other	$ 50	$ 231	$ 734	$ 786
Shares, ending balance (in shares)	1,026,000,000	918,000,000	1,026,000,000	918,000,000	1,026,000,000
Equity, ending balance	$ (54,925)	$ (46,166)	$ (54,925)	$ (46,166)	$ (54,925)
Non- controlling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	102	237	181	233	234
Net income (loss) attributable to noncontrolling interests	6	8	(73)	22
Distributions attributable to noncontrolling interests	(21)	(11)	(21)	(21)
Equity, ending balance	$ 87	$ 234	$ 87	$ 234	$ 87

Equity - Narrative (Details)

Equity - Narrative (Details) - USD ($) shares in Millions	Oct. 29, 2018	Apr. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Oct. 25, 2018
Accelerated Share Repurchases [Line Items]
Treasury stock shares acquired			$ 1,405,000,000	$ 996,000,000	$ 3,730,000,000	$ 3,158,000,000
Accelerated Share Repurchase Agreement
Accelerated Share Repurchases [Line Items]
Share repurchase program authorized amount								$ 5,000,000,000
Treasury stock shares purchased (in shares)	56.7	7.7					64.4
Payment under ASR agreement	$ 5,000,000,000
Treasury stock shares acquired	4,000,000,000
Decrease in other-paid-in capital	$ 1,000,000,000

Share-Based Compensation Plan_2

Share-Based Compensation Plans - Expense Allocations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement [Abstract]
Pretax share-based compensation expense	$ 101	$ 91	$ 306	$ 261
Income tax benefit	(14)	(14)	(42)	(42)
Total share-based compensation expense, net of taxes	$ 87	$ 77	$ 264	$ 219

Share-Based Compensation Plan_3

Share-Based Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)	3,000	3,000
Weighted- average exercise price of options granted in period (in dollars per share)	$ 80.05	$ 57.72
Weighted- average fair value per option granted (in dollars per share)	$ 10.63	$ 8.19
Total pretax unrecognized compensation expense related to nonvested stock options, RSU and PSU awards	$ 691
Weighted average period in years of recognition for nonvested stock options, RSU and PSU awards	2 years
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	5,000	7,000
Weighted-average fair value per share granted (in dollars per share)	$ 80.03	$ 58.19
Performance Share Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	609	855
Weighted-average fair value per share granted (in dollars per share)	$ 90.50	$ 56.70

Share-Based Compensation Plan_4

Share-Based Compensation Plans - Assumptions Used for Options Granted (Details)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement [Abstract]
Expected dividend yield	3.20%	3.40%
Risk-free interest rate	2.40%	2.80%
Expected volatility	18.70%	19.10%
Expected life (years)	5 years 10 months 24 days	6 years 1 month 6 days

Pension and Other Postretirem_3

Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 12	$ 15	$ 36	$ 43
Interest cost	17	17	52	52
Expected return on plan assets	(18)	(21)	(54)	(63)
Amortization of unrecognized prior service credit	(20)	(21)	(59)	(63)
Net loss amortization	(3)	0	(7)	1
Termination benefits	1	0	1	2
Curtailments	(3)	(1)	(4)	(7)
Net periodic benefit cost	(14)	(11)	(35)	(35)
U.S. | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	76	77	221	245
Interest cost	115	109	343	324
Expected return on plan assets	(202)	(209)	(613)	(634)
Amortization of unrecognized prior service credit	(12)	(12)	(37)	(37)
Net loss amortization	43	63	113	174
Termination benefits	3	1	7	18
Curtailments	5	3	6	7
Settlements	0	0	0	1
Net periodic benefit cost	28	32	40	98
International | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	58	56	178	181
Interest cost	44	43	133	134
Expected return on plan assets	(106)	(106)	(320)	(326)
Amortization of unrecognized prior service credit	(3)	(3)	(9)	(10)
Net loss amortization	16	21	47	64
Termination benefits	0	0	1	0
Curtailments	0	0	0	(1)
Settlements	0	0	0	3
Net periodic benefit cost	$ 9	$ 11	$ 30	$ 45

Other (Income) Expense, Net (De

Other (Income) Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Income and Expenses [Abstract]
Interest income	$ (61)	$ (92)	$ (225)	$ (257)
Interest expense	231	190	674	569
Exchange losses	38	42	166	119
Income from investments in equity securities, net (1)	(16)	(198)	(50)	(376)
Net periodic defined benefit plan (credit) cost other than service cost	(128)	(119)	(409)	(384)
Other, net	(29)	5	206	(183)
Other (income) expense, net	$ 35	$ (172)	362	(512)
Goodwill impairment charges			162
Gain on settlement				115
Other noncash income			84
Interest paid			$ 629	$ 535

Taxes on Income (Details)

Taxes on Income (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Examination [Line Items]
Effective income tax rate (as percent)	18.70%		26.50%	14.50%	27.60%
Internal Revenue Service (IRS) | Domestic Tax Authority
Income Tax Examination [Line Items]
Tax benefit recognized related to settlement				$ 360
Income taxes paid		$ 107

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income attributable to Merck & Co., Inc.	$ 1,901	$ 1,950	$ 7,487	$ 4,393
Average common shares outstanding	2,558	2,662	2,572	2,680
Common shares issuable (1)	14	16	15	14
Average common shares outstanding assuming dilution	2,572	2,678	2,587	2,694
Basic earnings per common share attributable to Merck & Co., Inc. common shareholders	$ 0.74	$ 0.73	$ 2.91	$ 1.64
Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders	$ 0.74	$ 0.73	$ 2.89	$ 1.63
Common shares issuable under share-based compensation plans excluded from diluted earnings per common share because the effect would have been antidilutive (in shares)	3	2	2	7

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	$ 27,737	$ 32,766	$ 26,882	$ 34,569
Other comprehensive income (loss) before reclassification adjustments, pretax	106	(110)	364	(143)
Tax	(72)	5	(65)	(130)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	34	(105)	299	(273)
Reclassification adjustments, pretax	(75)	84	(176)	365
Tax	13	(8)	32	(59)
Reclassification adjustments, net of taxes	(62)	76	(144)	306
Other comprehensive income (loss), net of taxes	(28)	(29)	155	33
Adoption of ASU 2018-02				(266)
Adoption of ASU 2016-01					$ (8)
Equity, ending balance	26,925	32,656	26,925	32,656
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	66	65	166	(108)
Other comprehensive income (loss) before reclassification adjustments, pretax	186	29	183	113
Tax	(39)	(6)	(38)	(24)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	147	23	145	89
Reclassification adjustments, pretax	(71)	5	(195)	169
Tax	15	(1)	41	(35)
Reclassification adjustments, net of taxes	(56)	4	(154)	134
Other comprehensive income (loss), net of taxes	91	27	(9)	223
Adoption of ASU 2018-02				(23)
Adoption of ASU 2016-01					0
Equity, ending balance	157	92	157	92
Investments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	48	(164)	(78)	(61)
Other comprehensive income (loss) before reclassification adjustments, pretax	8	8	139	(125)
Tax	0	0	0	1
Other comprehensive income (loss) before reclassification adjustments, net of taxes	8	8	139	(124)
Reclassification adjustments, pretax	(25)	32	(30)	68
Tax	0	0	0	0
Reclassification adjustments, net of taxes	(25)	32	(30)	68
Other comprehensive income (loss), net of taxes	(17)	40	109	(56)
Adoption of ASU 2018-02				1
Adoption of ASU 2016-01					(8)
Equity, ending balance	31	(124)	31	(124)
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(3,530)	(3,065)	(3,556)	(2,787)
Other comprehensive income (loss) before reclassification adjustments, pretax	(4)	0	(5)	(2)
Tax	0	0	6	4
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(4)	0	1	2
Reclassification adjustments, pretax	21	47	49	128
Tax	(2)	(7)	(9)	(24)
Reclassification adjustments, net of taxes	19	40	40	104
Other comprehensive income (loss), net of taxes	15	40	41	106
Adoption of ASU 2018-02				(344)
Adoption of ASU 2016-01					0
Equity, ending balance	(3,515)	(3,025)	(3,515)	(3,025)
Cumulative Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(1,946)	(1,958)	(2,077)	(1,954)
Other comprehensive income (loss) before reclassification adjustments, pretax	(84)	(147)	47	(129)
Tax	(33)	11	(33)	(111)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(117)	(136)	14	(240)
Reclassification adjustments, pretax	0	0	0	0
Tax	0	0	0	0
Reclassification adjustments, net of taxes	0	0	0	0
Other comprehensive income (loss), net of taxes	(117)	(136)	14	(240)
Adoption of ASU 2018-02				100
Adoption of ASU 2016-01					$ 0
Equity, ending balance	(2,063)	(2,094)	(2,063)	(2,094)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(5,362)	(5,122)	(5,545)	(4,910)
Equity, ending balance	$ (5,390)	$ (5,151)	$ (5,390)	$ (5,151)

Segment Reporting - Narrative (

Segment Reporting - Narrative (Details) $ in Billions	3 Months Ended		9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)segment	Sep. 30, 2018USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment			4
Sales discounts | $	$ 3	$ 2.6	$ 8.6	$ 7.7

Segment Reporting - Sales of Co

Segment Reporting - Sales of Company's Products (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Sales	$ 12,397	$ 10,794	$ 34,972	$ 31,296
Operating Segments
Segment Reporting Information [Line Items]
Sales	12,263	10,734	34,622	31,230
Other
Segment Reporting Information [Line Items]
Sales	134	60	350	66
United States
Segment Reporting Information [Line Items]
Sales	5,525	5,030	15,183	13,425
United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	5,515	5,010	15,164	13,324
United States | Other
Segment Reporting Information [Line Items]
Sales	10	20	19	101
International
Segment Reporting Information [Line Items]
Sales	6,872	5,764	19,789	17,871
International | Operating Segments
Segment Reporting Information [Line Items]
Sales	6,747	5,725	19,459	17,906
International | Other
Segment Reporting Information [Line Items]
Sales	125	39	330	(35)
Total Pharmaceutical segment sales | Operating Segments
Segment Reporting Information [Line Items]
Sales	11,095	9,658	31,218	27,859
Total Pharmaceutical segment sales | Operating Segments | Keytruda
Segment Reporting Information [Line Items]
Sales	3,070	1,889	7,973	5,020
Total Pharmaceutical segment sales | Operating Segments | Emend
Segment Reporting Information [Line Items]
Sales	98	123	336	396
Total Pharmaceutical segment sales | Operating Segments | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	123	49	313	125
Total Pharmaceutical segment sales | Operating Segments | Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	109	43	280	78
Total Pharmaceutical segment sales | Operating Segments | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	1,320	1,048	3,044	2,317
Total Pharmaceutical segment sales | Operating Segments | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	623	525	1,794	1,343
Total Pharmaceutical segment sales | Operating Segments | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	237	214	592	586
Total Pharmaceutical segment sales | Operating Segments | RotaTeq
Segment Reporting Information [Line Items]
Sales	180	191	564	540
Total Pharmaceutical segment sales | Operating Segments | Vaqta
Segment Reporting Information [Line Items]
Sales	62	66	167	167
Total Pharmaceutical segment sales | Operating Segments | Bridion
Segment Reporting Information [Line Items]
Sales	284	217	817	661
Total Pharmaceutical segment sales | Operating Segments | Noxafil
Segment Reporting Information [Line Items]
Sales	177	188	560	551
Total Pharmaceutical segment sales | Operating Segments | Cubicin
Segment Reporting Information [Line Items]
Sales	52	95	207	287
Total Pharmaceutical segment sales | Operating Segments | Primaxin
Segment Reporting Information [Line Items]
Sales	77	72	207	212
Total Pharmaceutical segment sales | Operating Segments | Invanz
Segment Reporting Information [Line Items]
Sales	57	137	206	437
Total Pharmaceutical segment sales | Operating Segments | Cancidas
Segment Reporting Information [Line Items]
Sales	62	79	191	257
Total Pharmaceutical segment sales | Operating Segments | Simponi
Segment Reporting Information [Line Items]
Sales	203	210	625	673
Total Pharmaceutical segment sales | Operating Segments | Remicade
Segment Reporting Information [Line Items]
Sales	101	135	322	459
Total Pharmaceutical segment sales | Operating Segments | Belsomra
Segment Reporting Information [Line Items]
Sales	80	66	223	191
Total Pharmaceutical segment sales | Operating Segments | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	250	275	752	860
Total Pharmaceutical segment sales | Operating Segments | Zepatier
Segment Reporting Information [Line Items]
Sales	83	104	304	347
Total Pharmaceutical segment sales | Operating Segments | Zetia
Segment Reporting Information [Line Items]
Sales	147	165	443	696
Total Pharmaceutical segment sales | Operating Segments | Vytorin
Segment Reporting Information [Line Items]
Sales	57	92	231	414
Total Pharmaceutical segment sales | Operating Segments | Atozet
Segment Reporting Information [Line Items]
Sales	97	84	283	258
Total Pharmaceutical segment sales | Operating Segments | Adempas
Segment Reporting Information [Line Items]
Sales	107	94	302	238
Total Pharmaceutical segment sales | Operating Segments | Januvia
Segment Reporting Information [Line Items]
Sales	807	927	2,539	2,756
Total Pharmaceutical segment sales | Operating Segments | Janumet
Segment Reporting Information [Line Items]
Sales	503	563	1,567	1,693
Total Pharmaceutical segment sales | Operating Segments | NuvaRing
Segment Reporting Information [Line Items]
Sales	241	234	700	686
Total Pharmaceutical segment sales | Operating Segments | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	199	186	581	535
Total Pharmaceutical segment sales | Operating Segments | Singulair
Segment Reporting Information [Line Items]
Sales	152	161	503	521
Total Pharmaceutical segment sales | Operating Segments | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	116	103	329	348
Total Pharmaceutical segment sales | Operating Segments | Nasonex
Segment Reporting Information [Line Items]
Sales	58	71	226	274
Total Pharmaceutical segment sales | Operating Segments | Arcoxia
Segment Reporting Information [Line Items]
Sales	72	83	221	249
Total Pharmaceutical segment sales | Operating Segments | Follistim AQ
Segment Reporting Information [Line Items]
Sales	62	60	182	198
Total Pharmaceutical segment sales | Operating Segments | Other Pharmaceutical
Segment Reporting Information [Line Items]
Sales	1,229	1,109	3,634	3,486
Total Pharmaceutical segment sales | United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	5,132	4,649	14,065	12,206
Total Pharmaceutical segment sales | United States | Operating Segments | Keytruda
Segment Reporting Information [Line Items]
Sales	1,743	1,109	4,525	2,906
Total Pharmaceutical segment sales | United States | Operating Segments | Emend
Segment Reporting Information [Line Items]
Sales	42	71	173	239
Total Pharmaceutical segment sales | United States | Operating Segments | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	71	33	186	88
Total Pharmaceutical segment sales | United States | Operating Segments | Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	65	30	169	49
Total Pharmaceutical segment sales | United States | Operating Segments | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	761	740	1,579	1,422
Total Pharmaceutical segment sales | United States | Operating Segments | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	482	429	1,325	1,097
Total Pharmaceutical segment sales | United States | Operating Segments | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	179	160	428	394
Total Pharmaceutical segment sales | United States | Operating Segments | RotaTeq
Segment Reporting Information [Line Items]
Sales	102	134	360	384
Total Pharmaceutical segment sales | United States | Operating Segments | Vaqta
Segment Reporting Information [Line Items]
Sales	36	36	103	95
Total Pharmaceutical segment sales | United States | Operating Segments | Bridion
Segment Reporting Information [Line Items]
Sales	133	96	381	272
Total Pharmaceutical segment sales | United States | Operating Segments | Noxafil
Segment Reporting Information [Line Items]
Sales	77	89	268	257
Total Pharmaceutical segment sales | United States | Operating Segments | Cubicin
Segment Reporting Information [Line Items]
Sales	14	55	78	150
Total Pharmaceutical segment sales | United States | Operating Segments | Primaxin
Segment Reporting Information [Line Items]
Sales	2	1	2	6
Total Pharmaceutical segment sales | United States | Operating Segments | Invanz
Segment Reporting Information [Line Items]
Sales	(1)	74	30	252
Total Pharmaceutical segment sales | United States | Operating Segments | Cancidas
Segment Reporting Information [Line Items]
Sales	0	2	5	10
Total Pharmaceutical segment sales | United States | Operating Segments | Simponi
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Remicade
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Belsomra
Segment Reporting Information [Line Items]
Sales	23	23	68	76
Total Pharmaceutical segment sales | United States | Operating Segments | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	102	123	304	383
Total Pharmaceutical segment sales | United States | Operating Segments | Zepatier
Segment Reporting Information [Line Items]
Sales	24	18	96	8
Total Pharmaceutical segment sales | United States | Operating Segments | Zetia
Segment Reporting Information [Line Items]
Sales	5	9	11	34
Total Pharmaceutical segment sales | United States | Operating Segments | Vytorin
Segment Reporting Information [Line Items]
Sales	5	0	11	11
Total Pharmaceutical segment sales | United States | Operating Segments | Atozet
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Adempas
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Januvia
Segment Reporting Information [Line Items]
Sales	367	498	1,223	1,466
Total Pharmaceutical segment sales | United States | Operating Segments | Janumet
Segment Reporting Information [Line Items]
Sales	129	225	462	625
Total Pharmaceutical segment sales | United States | Operating Segments | NuvaRing
Segment Reporting Information [Line Items]
Sales	202	193	593	550
Total Pharmaceutical segment sales | United States | Operating Segments | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	136	133	421	375
Total Pharmaceutical segment sales | United States | Operating Segments | Singulair
Segment Reporting Information [Line Items]
Sales	11	5	24	16
Total Pharmaceutical segment sales | United States | Operating Segments | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	6	4	16	18
Total Pharmaceutical segment sales | United States | Operating Segments | Nasonex
Segment Reporting Information [Line Items]
Sales	4	7	2	8
Total Pharmaceutical segment sales | United States | Operating Segments | Arcoxia
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Follistim AQ
Segment Reporting Information [Line Items]
Sales	27	26	80	83
Total Pharmaceutical segment sales | United States | Operating Segments | Other Pharmaceutical
Segment Reporting Information [Line Items]
Sales	385	326	1,142	932
Total Pharmaceutical segment sales | International | Operating Segments
Segment Reporting Information [Line Items]
Sales	5,962	5,010	17,153	15,653
Total Pharmaceutical segment sales | International | Operating Segments | Keytruda
Segment Reporting Information [Line Items]
Sales	1,327	780	3,448	2,114
Total Pharmaceutical segment sales | International | Operating Segments | Emend
Segment Reporting Information [Line Items]
Sales	56	52	163	157
Total Pharmaceutical segment sales | International | Operating Segments | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	53	15	126	37
Total Pharmaceutical segment sales | International | Operating Segments | Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	44	13	112	29
Total Pharmaceutical segment sales | International | Operating Segments | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	558	308	1,464	894
Total Pharmaceutical segment sales | International | Operating Segments | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	141	96	469	246
Total Pharmaceutical segment sales | International | Operating Segments | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	58	54	164	192
Total Pharmaceutical segment sales | International | Operating Segments | RotaTeq
Segment Reporting Information [Line Items]
Sales	78	57	203	156
Total Pharmaceutical segment sales | International | Operating Segments | Vaqta
Segment Reporting Information [Line Items]
Sales	26	30	65	72
Total Pharmaceutical segment sales | International | Operating Segments | Bridion
Segment Reporting Information [Line Items]
Sales	151	120	437	389
Total Pharmaceutical segment sales | International | Operating Segments | Noxafil
Segment Reporting Information [Line Items]
Sales	100	99	291	294
Total Pharmaceutical segment sales | International | Operating Segments | Cubicin
Segment Reporting Information [Line Items]
Sales	38	40	129	137
Total Pharmaceutical segment sales | International | Operating Segments | Primaxin
Segment Reporting Information [Line Items]
Sales	75	71	204	206
Total Pharmaceutical segment sales | International | Operating Segments | Invanz
Segment Reporting Information [Line Items]
Sales	58	62	176	185
Total Pharmaceutical segment sales | International | Operating Segments | Cancidas
Segment Reporting Information [Line Items]
Sales	62	77	187	247
Total Pharmaceutical segment sales | International | Operating Segments | Simponi
Segment Reporting Information [Line Items]
Sales	203	210	625	673
Total Pharmaceutical segment sales | International | Operating Segments | Remicade
Segment Reporting Information [Line Items]
Sales	101	135	322	459
Total Pharmaceutical segment sales | International | Operating Segments | Belsomra
Segment Reporting Information [Line Items]
Sales	57	43	155	115
Total Pharmaceutical segment sales | International | Operating Segments | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	149	151	449	477
Total Pharmaceutical segment sales | International | Operating Segments | Zepatier
Segment Reporting Information [Line Items]
Sales	59	86	208	339
Total Pharmaceutical segment sales | International | Operating Segments | Zetia
Segment Reporting Information [Line Items]
Sales	142	157	432	662
Total Pharmaceutical segment sales | International | Operating Segments | Vytorin
Segment Reporting Information [Line Items]
Sales	52	92	219	402
Total Pharmaceutical segment sales | International | Operating Segments | Atozet
Segment Reporting Information [Line Items]
Sales	97	84	283	258
Total Pharmaceutical segment sales | International | Operating Segments | Adempas
Segment Reporting Information [Line Items]
Sales	107	94	302	238
Total Pharmaceutical segment sales | International | Operating Segments | Januvia
Segment Reporting Information [Line Items]
Sales	440	429	1,317	1,291
Total Pharmaceutical segment sales | International | Operating Segments | Janumet
Segment Reporting Information [Line Items]
Sales	375	339	1,105	1,067
Total Pharmaceutical segment sales | International | Operating Segments | NuvaRing
Segment Reporting Information [Line Items]
Sales	39	41	107	135
Total Pharmaceutical segment sales | International | Operating Segments | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	62	53	160	160
Total Pharmaceutical segment sales | International | Operating Segments | Singulair
Segment Reporting Information [Line Items]
Sales	140	156	479	505
Total Pharmaceutical segment sales | International | Operating Segments | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	110	99	313	330
Total Pharmaceutical segment sales | International | Operating Segments | Nasonex
Segment Reporting Information [Line Items]
Sales	55	64	224	266
Total Pharmaceutical segment sales | International | Operating Segments | Arcoxia
Segment Reporting Information [Line Items]
Sales	72	83	221	249
Total Pharmaceutical segment sales | International | Operating Segments | Follistim AQ
Segment Reporting Information [Line Items]
Sales	35	34	102	115
Total Pharmaceutical segment sales | International | Operating Segments | Other Pharmaceutical
Segment Reporting Information [Line Items]
Sales	842	786	2,492	2,557
Total Animal Health segment sales | Operating Segments
Segment Reporting Information [Line Items]
Sales	1,122	1,021	3,271	3,176
Total Animal Health segment sales | Operating Segments | Livestock
Segment Reporting Information [Line Items]
Sales	726	660	2,007	1,946
Total Animal Health segment sales | Operating Segments | Companion Animals
Segment Reporting Information [Line Items]
Sales	396	361	1,264	1,230
Total Animal Health segment sales | United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	337	306	966	924
Total Animal Health segment sales | United States | Operating Segments | Livestock
Segment Reporting Information [Line Items]
Sales	144	153	406	383
Total Animal Health segment sales | United States | Operating Segments | Companion Animals
Segment Reporting Information [Line Items]
Sales	193	153	560	541
Total Animal Health segment sales | International | Operating Segments
Segment Reporting Information [Line Items]
Sales	785	715	2,305	2,252
Total Animal Health segment sales | International | Operating Segments | Livestock
Segment Reporting Information [Line Items]
Sales	582	508	1,601	1,563
Total Animal Health segment sales | International | Operating Segments | Companion Animals
Segment Reporting Information [Line Items]
Sales	203	207	704	689
Other segment sales | Operating Segments
Segment Reporting Information [Line Items]
Sales	46	55	133	195
Other segment sales | United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	46	55	133	194
Other segment sales | International | Operating Segments
Segment Reporting Information [Line Items]
Sales	$ 0	$ 0	$ 1	$ 1

Segment Reporting - Revenues by

Segment Reporting - Revenues by Geographic Area (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue from External Customer [Line Items]
Sales	$ 12,397	$ 10,794	$ 34,972	$ 31,296
United States
Revenue from External Customer [Line Items]
Sales	5,525	5,030	15,183	13,425
Europe, Middle East and Africa
Revenue from External Customer [Line Items]
Sales	3,189	2,884	9,452	9,218
Japan
Revenue from External Customer [Line Items]
Sales	919	761	2,639	2,353
China
Revenue from External Customer [Line Items]
Sales	914	512	2,423	1,556
Asia Pacific (other than Japan and China)
Revenue from External Customer [Line Items]
Sales	756	666	2,217	2,210
Latin America
Revenue from External Customer [Line Items]
Sales	671	622	1,889	1,748
Other
Revenue from External Customer [Line Items]
Sales	$ 423	$ 319	$ 1,169	$ 786

Segment Reporting - Profits to

Segment Reporting - Profits to Income Before Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Profits	$ 2,347	$ 2,665	$ 8,673	$ 6,097
Interest income	61	92	225	257
Interest expense	(231)	(190)	(674)	(569)
Depreciation and amortization			(2,716)	(3,521)
Research and development	(3,204)	(2,068)	(7,324)	(7,538)
Restructuring costs	(232)	(171)	(444)	(494)
Charge related to termination of collaboration agreement with Samsung			0	(420)
Total segment profits
Segment Reporting Information [Line Items]
Profits	8,168	7,035	22,678	19,902
Total segment profits | Pharmaceutical segment
Segment Reporting Information [Line Items]
Profits	7,747	6,621	21,437	18,535
Total segment profits | Animal Health segment
Segment Reporting Information [Line Items]
Profits	423	409	1,243	1,273
Total segment profits | Other segments
Segment Reporting Information [Line Items]
Profits	(2)	5	(2)	94
Other profits (losses)
Segment Reporting Information [Line Items]
Profits	101	55	226	(35)
Unallocated
Segment Reporting Information [Line Items]
Interest income	61	92	225	257
Interest expense	(231)	(190)	(674)	(569)
Depreciation and amortization	(382)	(324)	(1,169)	(1,006)
Research and development	(3,110)	(1,997)	(7,045)	(7,304)
Amortization of purchase accounting adjustments	(329)	(679)	(1,105)	(2,144)
Restructuring costs	(232)	(171)	(444)	(494)
Charge related to termination of collaboration agreement with Samsung	0	(420)	0	(420)
Other unallocated, net	$ (1,699)	$ (736)	$ (4,019)	$ (2,090)