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Number Of Cases Remanded Loss Contingency, Number Of Cases Remanded Schedule of Inventory, noncurrent Schedule of Inventory, Noncurrent [Table Text Block] Share-based compensation Share-Based Payment Arrangement, Noncash Expense Derivative asset, notional amount Derivative Asset, Notional Amount Bayer AG Bayer AG [Member] Bayer AG [Member] Revenue related to the sale of the marketing rights Proceeds from Sale of Intangible Assets Employee Stock Option Share-Based Payment Arrangement, Option [Member] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Liable contracted portion of research and development expenses to incur costs for in collaborative arrangement Collaborative Arrangement, Rights And Obligations, Liable Contracted Portion Amount Of Research And Development Expenses To Incur Costs For Collaborative Arrangement, Rights And Obligations, Liable Contracted Portion Amount Of Research And Development Expenses To Incur Costs For Cash dividends declared on common stock Dividends, Common Stock, Cash Total Merck & Co., Inc. stockholders’ equity Equity, Attributable to Parent Measurement Frequency [Axis] Measurement Frequency [Axis] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-Sale [Table] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Other Comprehensive Income (Loss) Net of Taxes: Other Comprehensive Income (Loss), Net of Tax [Abstract] Insider Trading Policies and Procedures [Line Items] Common stock, authorized (in shares) Common Stock, Shares Authorized Hedging Designation [Domain] Hedging Designation [Domain] Other assets and liabilities, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other, Net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other, Net Patents Patents [Member] Current Assets Assets, Current [Abstract] Liabilities and Equity Liabilities and Equity Loss 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profits Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Other Noncurrent Liabilities Other Liabilities, Noncurrent Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Proceeds from issuance of debt Proceeds from Issuance of Debt Legal Costs Legal Costs, Policy [Policy Text Block] Accounts Receivable Factoring Collections Accounts Receivable Factoring Collections [Member] Accounts Receivable Factoring Collections Operating Segments Total segment profits Operating Segments [Member] Hedged items Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Comprehensive Income Attributable to Merck & Co., Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Name Measure Name Restructuring reserve, beginning balance Restructuring reserve, ending balance Restructuring Reserve 4.55% notes due 2032 4.55% notes due 2032 [Member] 4.55% notes due 2032 Schedule of Information About the Changes in Liabilities for Contingent Consideration Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Animal Health Animal Health Animal Health segment [Member] Animal Health segment [Member] Deferred Income Taxes Deferred Income Tax Liabilities, Net Document Fiscal Period Focus Document Fiscal Period Focus Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Award Timing Method Award Timing Method [Text Block] Litigation Case [Domain] Litigation Case [Domain] Alliance revenue - Koselugo Alliance revenue - Koselugo [Member] Alliance revenue - Koselugo sac-TMT sac-TMT [Member] sac-TMT Award Type Award Type [Axis] Foreign Currency Translation Adjustment Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Total Assets Assets 3.700% Notes due 2044 3.700% Notes due 2044 [Member] 3.700% Notes due 2044 Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Trading Symbol Trading Symbol Geographical [Domain] Geographical [Domain] Entity Address, City or Town Entity Address, City or Town Cash Flows from Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Inventories Inventory Disclosure [Text Block] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Net change in short-term borrowings Proceeds from (Repayments of) Short-Term Debt Income Statement Location [Domain] Statement of Income Location, Balance [Domain] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] Assets Assets, Fair Value Disclosure [Abstract] Entity Emerging Growth Company Entity Emerging Growth Company Gross amount subject to offset in master netting arrangements not offset in the condensed balance sheet, asset Derivative Asset, Subject to Master Netting Arrangement, Deduction of Financial Instrument Not Offset Harpoon Therapeutics, Inc. Harpoon Therapeutics, Inc. [Member] Harpoon Therapeutics, Inc. Cash dividends declared on common stock (in dollars per share) Common Stock, Dividends, Per Share, Declared Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding 4.15% notes due 2030 4.15% notes due 2030 [Member] 4.15% notes due 2030 Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Cash collateral advanced to counterparties Cash collateral received, liability Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Not Offset Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Loss contingency, number of appeals issued Loss Contingency, Patents Unpatentable, Number Of Appeals Issues Loss Contingency, Patents Unpatentable, Number Of Appeals Issues Level 2 Fair Value, Inputs, Level 2 [Member] Amount of gain recognized in Other (income) expense, net on derivatives Derivative, Gain (Loss) on Derivative, Net Restricted cash Restricted Cash and Cash Equivalent Restructuring Reserve [Roll Forward] Restructuring Reserve [Roll Forward] Third-Party Third-Party [Member] Third-Party Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Business Combination [Domain] Business Combination [Domain] Januvia Januvia [Member] Januvia [Member] . 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Alteogen Inc. [Member] Alteogen Inc. Document Fiscal Year Focus Document Fiscal Year Focus Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Payments on debt Repayments of Long-Term Debt Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Number of antibody drug conjugates obtained right and obligations Collaborative Arrangement, Rights And Obligations, Number Of Antibody Drug Conjugates Collaborative Arrangement, Rights And Obligations, Number Of Antibody Drug Conjugates Entity Interactive Data Current Entity Interactive Data Current Schedule of Effect of Net Investment Hedges on OCI and the Consolidated Statement of Operations Schedule of Net Investment Hedges in Accumulated Other Comprehensive Income (Loss) [Table Text Block] Recognized as: Recognized As [Abstract] Recognized as. 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Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Local Phone Number Local Phone Number Class of Stock [Domain] Class of Stock [Domain] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Other Payment for (Proceeds from) Other Investing Activity Moderna, Inc. Moderna, Inc. [Member] Moderna, Inc. Subsequent Event Type [Axis] Subsequent Event Type [Axis] Liabilities resulting milestone payments Collaborative Arrangement, Rights And Obligations, Liabilities Resulting From Milestone Payments Collaborative Arrangement, Rights And Obligations, Liabilities Resulting From Milestone Payments Future fixed upfront payments received Collaborative Arrangement, Future Fixed Upfront Payments Collaborative Arrangement, Future Fixed Upfront Payments Schedule of Information on Derivative Positions Subject to Master Netting Arrangements as if they were Presented on a Net Basis Offsetting Assets And Liabilities [Table Text Block] Tabular disclosure of derivative positions subject to master netting arrangements as if they were presented on a net basis. Expected restructuring and related cost Restructuring and Related Cost, Expected Cost Assets Assets [Abstract] Long-Term Debt Long-Term Debt, Excluding Current Maturities Inventories classified in other assets Other Assets Inventory, Noncurrent Underlying Security Market Price Change Underlying Security Market Price Change, Percent Balance Sheet Location [Axis] Statement of Financial Position Location, Balance [Axis] Simponi Simponi [Member] Simponi [Member]. Debt Instrument [Axis] Debt Instrument [Axis] Total debt and publicly traded equity securities, fair value Debt Securities and Equity Securities, FV-NI Debt Securities and Equity Securities, FV-NI Aqua manufacturing facilities Aqua Manufacturing Facilities Aqua Manufacturing Facilities Pension and Other Postretirement Benefit Plans Retirement Benefits [Text Block] Business Combination [Line Items] Business Combination [Line Items] Reclassification adjustments, pretax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Merck & Co., Inc. Stockholders’ Equity Equity, Attributable to Parent [Abstract] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Entity Address, Address Line One Entity Address, Address Line One Regulatory milestone payments Collaborative Arrangement, Rights and Obligations, Milestone Payments, Regulatory Collaborative Arrangement, Rights and Obligations, Milestone Payments, Regulatory Treasury stock shares purchased Treasury Stock, Value, Acquired, Cost Method Research and development Research and development Research and Development Expense Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Stated interest rate Debt Instrument, Interest Rate, Stated Percentage Allowance for doubtful accounts Accounts Receivable, Allowance for Credit Loss, Current Non-cash activity Restructuring Reserve, Increase (Decrease) Noncash Activity Noncash activity affecting the restructuring reserve, including accelerated depreciation. Schedule of Sales from Products Revenue from External Customers by Products and Services [Table Text Block] Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract] Loss contingency, companies settled with, minimum number Loss Contingency, Companies Settled With, Minimum Number Loss Contingency, Companies Settled With, Minimum Number Subcutaneous Pembrolizumab Subcutaneous Pembrolizumab [Member] Subcutaneous Pembrolizumab Proceeds from sales of securities and other investments Proceeds from Sale and Maturity of Other Investments Other, net Other Nonoperating Income Expense, Other Other nonoperating income and expense items not separately disclosed. Amortization of unrecognized prior service credit Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Gross amounts recognized in the consolidated balance sheet, asset Derivative Asset, Subject to Master Netting Arrangement, before Offset Fair Value as of Grant Date Award Grant Date Fair Value Restructuring Program, 2025 Restructuring Program, 2025 [Member] Restructuring Program, 2025 Entity Registrant Name Entity Registrant Name Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Schedule of Other (Income) Expense, Net Schedule of Other Nonoperating Income (Expense) [Table Text Block] Keytruda Keytruda [Member] Keytruda [Member] LaNova Medicines Ltd LaNova Medicines Ltd [Member] LaNova Medicines Ltd Purchases of securities and other investments Payments to Acquire Investments Document Quarterly Report Document Quarterly Report Alliance revenue - Adempas/Verquvo Alliance revenue - Adempas/Verquvo [Member] Alliance revenue - Adempas/Verquvo Total assets Assets, Fair Value Disclosure Acquisition of Harpoon Therapeutics, Inc., net of cash acquired Payments to Acquire Business Three, Net of Cash Acquired Change in Unrecognized Tax Benefit, Reasonably Possible [Table] Change in Unrecognized Tax Benefit, Reasonably Possible [Table] Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Counterparty Name [Domain] Counterparty Name [Domain] Equity investments without readily determinable fair values Equity Securities without Readily Determinable Fair Value, Amount Number of operating segments Number of Operating Segments Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] Interest cost Defined Benefit Plan, Interest Cost Investments Investments Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Other Noncurrent Liabilities Other Noncurrent Liabilities [Member] Capitalization of shared costs Prepaid Expense and Other Assets Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Restatement Determination Date: Restatement Determination Date [Axis] Cash paid for acquisition of business Payments to Acquire Businesses, Gross Non-PEO NEO Non-PEO NEO [Member] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Schedule of Charges Related to Restructuring Program Activities by Type of Cost Restructuring and Related Costs [Table Text Block] Liable contracted portion of research and development expenses to incur costs for in collaborative arrangement, percentage Collaborative Arrangement, Rights And Obligations, Liable Contracted Portion Amount Of Research And Development Expenses To Incur Costs For, Percentage Collaborative Arrangement, Rights And Obligations, Liable Contracted Portion Amount Of Research And Development Expenses To Incur Costs For, Percentage Refundable upfront payments in collaborative arrangement Collaborative Arrangement, Rights And Obligations, Refundable Upfront Payments Collaborative Arrangement, Rights And Obligations, Refundable Upfront Payments Schedule of Interest Rate Swaps Held Schedule of Interest Rate Derivatives [Table Text Block] Other Proceeds from (Payment for) Other Financing Activity Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Reclassification adjustments, net of taxes Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Commercial and Other Litigation Commercial and Other Litigation [Member] Commercial and Other Litigation Derivative liability, notional amount Derivative Liability, Notional Amount Debt securities, unrealized gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Name Trading Arrangement, Individual Name All Award Types Award Type [Domain] Amount of gain (loss) recognized in OCI on derivatives Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax Noncontrolling Interests Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Other Other Noncash Income (Expense) Product Rights Product Rights [Member] Product Rights Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Compensation Amount Outstanding Recovery Compensation Amount Par Value of Debt Face amount of debt Debt Instrument, Face Amount Schedule of Consolidated Sales by Geographic Area Schedule of Revenue from External Customers Attributed to Foreign Countries by Geographic Area [Table Text Block] Lynparza Lynparza [Member] Lynparza [Member] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Foreign exchange contracts Foreign Exchange Contract [Member] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Restructuring costs Restructuring Charges [Member] Total current and noncurrent inventories Inventory Net And Inventory Noncurrent Total of current and noncurrent inventories. Loss contingency, number of patents allegedly infringed Loss Contingency, Patents Allegedly Infringed, Number Retirement Plan Type [Domain] Retirement Plan Type [Domain] China CHINA MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Equity Funds Equity Funds [Member] Name Awards Close in Time to MNPI Disclosures, Individual Name Asset acquisition, transaction costs Asset Acquisition, Consideration Transferred, Transaction Cost (Payments) receipts, net Payments for Restructuring Restructuring Type [Axis] Restructuring Type [Axis] Deferred tax asset Business Combination, Recognized Asset Acquired, Deferred Tax Asset Changes in estimated fair value Business Combination, Contingent Consideration, Change in Contingent Consideration, Liability, Increase (Decrease) Acquisitions, Research Collaborations and Licensing Agreements Acquisitions Research Collaborations And License Agreements [Text Block] Information related to acquisitions, divestitures, research collaborations and license agreements. Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Net changes in assets and liabilities Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital Currency options Foreign Exchange Option [Member] Cash equivalents Cash Equivalents, at Carrying Value 1.375% Notes due 2036 1.375% Notes due 2036 [Member] 1.375% Notes due 2036 [Member] Inventory [Domain] Inventory [Domain] Gross amount subject to offset in master netting arrangements not offset in the condensed balance sheet, liability Derivative Liability, Subject to Master Netting Arrangement, Deduction of Financial Instrument Not Offset Collaborative arrangement, rights and obligations, probable contingent payments Collaborative Arrangement, Rights And Obligations, Probable Contingent Payments Collaborative Arrangement, Rights And Obligations, Probable Contingent Payments Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] Hedged Liability, Statement of Financial Position [Extensible Enumeration] Hedged Liability, Statement of Financial Position [Extensible Enumeration] Alliance Revenue - Reblozyl Alliance Revenue - Reblozyl [Member] Alliance Revenue - Reblozyl Tax Other Comprehensive Income (Loss) before Reclassifications, Tax Financial Instruments Financial Instruments [Domain] Litigation Case [Axis] Litigation Case [Axis] Segments [Domain] Segments [Domain] Januvia, Janumet, Janumet XR Januvia, Janumet, Janumet XR [Member] Januvia, Janumet, Janumet XR Income Statement Location [Axis] Statement of Income Location, Balance [Axis] Europe, Middle East and Africa EMEA [Member] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Balance Sheet Location [Domain] Statement of Financial Position Location, Balance [Domain] Inventories (excludes inventories of $5,412 in 2025 and $4,193 in 2024 classified in Other assets - see Note 6) Inventories Inventory, Net Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Minimum Minimum [Member] Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] Ridgeback Biotherapeutics LP Ridgeback Biotherapeutics LP [Member] Ridgeback Biotherapeutics LP Cash collateral received from counterparties Cash collateral received, asset Derivative Asset, Subject to Master Netting Arrangement, Collateral, Obligation to Return Cash Not Offset Qui Tam Qui Tam [Member] Qui Tam Accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Loss contingency, claims settled, number of companies Loss Contingency, Claims Settled, Number Of Companies Loss Contingency, Claims Settled, Number Of Companies Sales based royalty percentage Collaborative Arrangement, Rights And Obligations, Royalty Percentage On Sales Collaborative Arrangement, Rights And Obligations, Royalty Percentage On Sales Company Selected Measure Name Company Selected Measure Name Total Costs, Expenses and Other Costs Expenses And Other Total of cost of sales, operating expenses and nonoperating income or expense. Senior Notes Senior Notes [Member] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Trade accounts payable Accounts Payable, Current Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Net Income Attributable to Merck & Co., Inc., diluted Net Income (Loss) Available to Common Stockholders, Diluted All Executive Categories All Executive Categories [Member] Royalty rate Royalty Rate, Percentage Royalty Rate, Percentage Capvaxive Capvaxive [Member] Capvaxive Common stock, $0.50 par value Authorized - 6,500,000,000 shares Issued - 3,577,103,522 shares in 2025 and 2024 Common Stock, Value, Issued Number of plaintiffs in complaint Number Of Plaintiffs In Complaint Number Of Plaintiffs In Complaint Restructuring Plan [Domain] Restructuring Plan [Domain] Derivatives designated as hedging instruments Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments Contingencies Commitments and Contingencies Disclosure [Text Block] Average common shares outstanding assuming dilution (in shares) Weighted Average Number of Shares Outstanding, Diluted Eyebiotech Limited Eyebiotech Limited [Member] Eyebiotech Limited Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Derivative [Table] Derivative [Table] Product rights and other Business Combination, Recognized Asset Acquired, Identifiable Intangible Asset, Finite-Lived Business Combination [Axis] Business Combination [Axis] Entity Small Business Entity Small Business Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Income Tax Estimation, Estimation Expense Type [Axis] Income Tax Estimation, Estimation Expense Type [Axis] Income Tax Estimation, Estimation Expense Type Non- controlling Interests Noncontrolling Interest [Member] Other Other Countries [Member] Other Countries [Member] Maximum average period of maturities of contracts in years (less than) Derivative, Average Remaining Maturity Long-Term Debt Long-Term Debt [Text Block] Document Transition Report Document Transition Report Underlying Securities Award Underlying Securities Amount Other comprehensive income (loss) before reclassification adjustments, pretax Other Comprehensive Income (Loss), before Reclassifications, before Tax Equity Component [Domain] Equity Component [Domain] Cumulative Amount of Fair Value Hedging Adjustment Increase Included in the Carrying Amount Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease) Document Period End Date Document Period End Date PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount 5.70% notes due 2055 5.70% notes due 2055 [Member] 5.70% notes due 2055 Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Carrying Amount of Hedged Liabilities Hedged Liability, Fair Value Hedge Income Taxes Income Tax Disclosure [Text Block] Other Product Rights Other Product Rights [Member] Other Product Rights Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] 5.00% note due 2053 5.00% note due 2053 [Member] 5.00% note due 2053 Hedging Designation [Axis] Hedging Designation [Axis] Fair value of loans payable and long-term debt, including current portion Debt Instrument, Fair Value Disclosure Bristol Myers Squibb Company Bristol Myers Squibb Company [Member] Bristol Myers Squibb Company MK-1045/CN201, Curon Biopharmaceutical MK-1045/CN201, Curon Biopharmaceutical [Member] MK-1045/CN201, Curon Biopharmaceutical Scenario [Axis] Scenario [Axis] Total equity Equity, beginning balance Equity, ending balance Equity, Including Portion Attributable to Noncontrolling Interest Document Type Document Type Level 3 Fair Value, Inputs, Level 3 [Member] Earnings Per Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Loss Contingencies [Table] Loss Contingencies [Table] Product and Service [Axis] Product and Service [Axis] Domestic Plan Domestic Plan [Member] (Decrease) increase in Sales as a result of AOCL reclassifications Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Derivative Contract [Domain] Derivative Contract [Domain] Asset Acquisition [Domain] Asset Acquisition [Domain] Litigation Status [Domain] Litigation Status [Domain] Collaborative Arrangement, Transaction with Party to Collaborative Arrangement Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member] All Individuals All Individuals [Member] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Capital expenditures Payments to Acquire Property, Plant, and Equipment Prevymis Prevymis [Member] Prevymis [Member] Verquvo Verquvo [Member] Verquvo Consideration transferred, asset acquisition Asset Acquisition, Consideration Transferred Name Forgone Recovery, Individual Name Total current assets Other current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Sales milestone payments Collaborative Arrangement, Rights And Obligations, Maximum Aggregate Sales-Based Milestone Payments Collaborative Arrangement, Rights And Obligations, Maximum Aggregate Sales-Based Milestone Payments HRS-5346 , Jiangsu Hengrui Pharmaceuticals Co., Ltd. HRS-5346 , Jiangsu Hengrui Pharmaceuticals Co., Ltd. [Member] HRS-5346 , Jiangsu Hengrui Pharmaceuticals Co., Ltd. Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Ifinatamab Deruxtecan Ifinatamab Deruxtecan [Member] Ifinatamab Deruxtecan 2.500% Notes due 2034 2.500% Notes due 2034 [Member] 2.500% Notes due 2034 [Member] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Effective income tax rate reconciliation, tax contingency, favorable impact, percent Effective Income Tax Rate Reconciliation, Tax Contingency, Domestic, Percent Net Income Attributable to Merck & Co., Inc., basic Net Income (Loss) Available to Common Stockholders, Basic Short-term investments Marketable Securities, Current Entity Information [Line Items] Entity Information [Line Items] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Schedule of Reconciliation of Segment Profits to Income before Taxes Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block] Current Liabilities Liabilities, Current [Abstract] Other comprehensive income (loss), net of taxes Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Geographical [Axis] Geographical [Axis] Net assets acquired Asset Acquisition, Assets Acquired And Liabilities Assumed, Net Asset Acquisition, Assets Acquired And Liabilities Assumed, Net Schedule of Amounts Recorded on Balance Sheet Related to Fair Value Hedges Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Schedule of Location and Amount of Pretax Gains and Losses of Derivatives Derivative Instruments, Gain (Loss) [Table Text Block] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Benefit plan net gain (loss) and prior service credit (cost), net of amortization Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax and Reclassification Adjustment, Attributable to Parent Level 1 Fair Value, Inputs, Level 1 [Member] Research and development Research And Development Expense (Reimbursement) Research And Development Expense (Reimbursement) Exchange losses Gain (Loss), Foreign Currency Transaction, before Tax Koselugo Koselugo [Member] Koselugo Asia Pacific (other than China and Japan) Asia Pacific [Member] Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share) Earnings Per Share, Diluted Forecast Forecast [Member] Aggregate, regulatory milestones payments, maximum Collaborative Arrangement, Rights And Obligations, Maximum Aggregate Regulatory Milestone Payments Collaborative Arrangement, Rights And Obligations, Maximum Aggregate Regulatory Milestone Payments Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Accounts receivable (net of allowance for doubtful accounts of $93 in 2025 and $89 in 2024) Accounts Receivable, after Allowance for Credit Loss, Current Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Title of 12(b) Security Title of 12(b) Security Accumulated Other Comprehensive Income (Loss) [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Euro-denominated notes Euro-dominated Notes [Member] Euro-dominated Notes [Member] Loss contingency, number of plaintiffs Loss Contingency, Number of Plaintiffs Royalty rate, deduction Royalty Rate, Deduction, Percentage Royalty Rate, Deduction, Percentage PGR Petition Process, Ineligible to be Challenged PGR Petition Process, Ineligible to be Challenged [Member] PGR Petition Process, Ineligible to be Challenged Treasury stock (in shares) Treasury stock, beginning balance (in shares) Treasury stock, ending balance (in shares) Treasury Stock, Common, Shares Earnings Per Share [Abstract] Earnings Per Share [Abstract] Restructuring Plan [Axis] Restructuring Plan [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Derivative Liability, Statement of Financial Position [Extensible Enumeration] Derivative Liability, Statement of Financial Position [Extensible Enumeration] Net assets acquired Asset Acquisition, Maximum Aggregate Contingent Development, Regulatory, and Sales-Based-Related Payments Asset Acquisition, Maximum Aggregate Contingent Development, Regulatory, and Sales-Based-Related Payments Bridion Bridion [Member] Bridion [Member]. U.S. government and agency securities Debt Securities, Available-for-Sale, Current Patritumab Deruxtecan Patritumab Deruxtecan [Member] Patritumab Deruxtecan Eisai Eisai [Member] Eisai [Member] Asset under Construction Asset under Construction [Member] Share-based compensation plans and other Stockholders' Equity, Other Welireg Welireg [Member] Welireg Publicly traded equity securities Equity Securities, FV-NI, Noncurrent Treasury stock shares purchased (in shares) Treasury Stock, Shares, Acquired Restricted Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents [Axis] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Award Timing Disclosures [Line Items] Schedule of Inventory, current Schedule of Inventory, Current [Table Text Block] Service cost Defined Benefit Plan, Service Cost Measurement Frequency [Domain] Measurement Frequency [Domain] Other comprehensive income (loss) before reclassification adjustments, net of taxes Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Charges for research and development asset acquisitions Research and Development Asset Acquired in Transaction Other than Business Combination or Joint Venture Formation, Writeoff Pharmaceutical Pharma- ceutical Pharmaceutical segment [Member] Pharmaceutical segment. Developmental milestone payment triggered and paid Asset Acquisition, Milestone Payment Triggered and Paid, Development Asset Acquisition, Milestone Payment Triggered and Paid, Development Equity Equity [Text Block] Income Tax Estimation, Estimation Expense Type [Domain] Income Tax Estimation, Estimation Expense Type [Domain] Income Tax Estimation, Estimation Expense Type [Domain] Distributions attributable to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Net Income Attributable to Merck & Co., Inc. Net Income Attributable to Merck & Co., Inc. Net income attributable to Merck & Co., Inc. Net Income (Loss) Attributable to Parent Expiration Date Trading Arrangement Expiration Date Pending Litigation Pending Litigation [Member] Research and development arrangement, contract to perform for others, compensation earned Research and Development Arrangement, Contract to Perform for Others, Compensation Earned Unrealized net gains (losses) Equity Securities, FV-NI, Unrealized Gain (Loss) Property, Plant and Equipment, at cost, net of accumulated depreciation of $20,605 in 2025 and $19,155 in 2024 Property, plant and equipment, net Property, Plant and Equipment, Net Vaxneuvance Vaxneuvance [Member] Vaxneuvance Verona Pharma plc Verona Pharma plc [Member] Verona Pharma plc Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Restructuring costs Restructuring costs Restructuring Charges Purchases of treasury stock Payments for Repurchase of Common Stock Adoption Date Trading Arrangement Adoption Date Reclassifications Reclassification, Comparability Adjustment [Policy Text Block] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Schedule of Restructuring and Related Costs [Table] Restructuring Cost [Table] Entity Current Reporting Status Entity Current Reporting Status Acquisition of MK-1045 (formerly CN201) from Curon Pharmaceutical Payments to Acquire Global Rights Payments to Acquire Global Rights Inventories Produced in Preparation for Product Launches Inventories Produced in Preparation for Product Launches [Member] Inventories Produced in Preparation for Product Launches [Member] Derivative [Line Items] Derivative [Line Items] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Decrease to LIFO cost Inventory, LIFO Reserve Zetia Zetia [Member] Zetia Japan JAPAN Retained earnings Retained Earnings (Accumulated Deficit) Penalties Penalties [Member] Penalties Net amounts, liability Derivative Liability, Subject to Master Netting Arrangement, after Offset Financial Instrument Financial Instrument [Axis] Amount of Pretax Gain Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing Other Comprehensive Income (Loss), Net Investment Hedge, Gain (Loss), Reclassification, before Tax Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Executive Category: Executive Category [Axis] Pediatric exclusivity, term Pediatric Exclusivity, Term Pediatric Exclusivity, Term Gardasil/Gardasil 9 Gardasil/Gardasil 9 [Member] Gardasil/Gardasil 9 [Member]. Companion Animal Companion Animal [Member] Companion Animal [Member] Current Fiscal Year End Date Current Fiscal Year End Date Class of Stock [Axis] Class of Stock [Axis] 3.750% Notes due 2054 3.750% Notes due 2054 [Member] 3.750% Notes due 2054 Derivatives Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Remicade Remicade [Member] Remicade [Member]. Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Stockholders Equity [Table] Stockholders Equity [Table] Stockholders Equity [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Other (income) expense, net Other (income) expense, net Other segment items Other Nonoperating Income (Expense) Fair value of derivative, liability Derivative Liability Acquisition of Elanco Animal Health Incorporated aqua business Payments to Acquire Business Four Payments to Acquire Business Four Deferred income taxes Deferred Income Tax Expense (Benefit) Adjustments to reconcile net income to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Unrecognized tax benefits Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations Collaborative Arrangements Collaborative Arrangement Disclosure [Text Block] Cash Flows from Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Janumet Janumet [Member] Janumet [Member]. Interest rate contracts Interest Rate Contract [Member] Consideration transferred Business Combination, Recognized Asset Acquired to Liability Assumed, Excess (Less), and Goodwill Income tax rate, unfavorable discrete impact Effective Income Tax Rate Reconciliation, Nondeductible Expense, Research and Development, Percent Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Publicly traded equity securities, fair value Publicly traded equity securities Equity Securities, FV-NI, Current Total identifiable net assets Business Combination, Recognized Asset Acquired to Liability Assumed, Excess (Less) Antidilutive shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] All Adjustments to Compensation All Adjustments to Compensation [Member] Amendment Flag Amendment Flag Zerbaxa Zerbaxa [Member] Zerbaxa [Member] Dificid Dificid [Member] Dificid Other Postretirement Benefit Plans Other Postretirement Benefits Plan [Member] Less treasury stock, at cost: 1,089,754,712 shares in 2025 and 1,049,466,187 shares in 2024 Treasury Stock, Common, Value Termination Date Trading Arrangement Termination Date Net Cash Used in Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] Number of Interest Rate Swaps Held Number of Interest Rate Derivatives Held Increase in hedge revenue Increase (Decrease) In Hedge Revenue Increase (Decrease) In Hedge Revenue 4.95% notes due 2035 4.95% notes due 2035 [Member] 4.95% notes due 2035 U.S. government and agency securities Debt Securities, Available-for-Sale, Noncurrent Accelerated Depreciation Accelerated Depreciation [Member] Accelerated Depreciation [Member] Adempas Adempas [Member] Adempas Average common shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Long-Lived Tangible Asset [Domain] Long-Lived Tangible Asset [Domain] Cost of sales Cost of Product and Service Sold Schedule of Calculations of Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Alliance revenue - Lynparza Alliance revenue - Lynparza [Member] Alliance revenue - Lynparza [Member] Discount rate Business Combination, Discount Rate Business Combination, Discount Rate Segment Reporting [Abstract] Segment Reporting [Abstract] Livestock Livestock [Member] Livestock [Member] Termination benefits Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Debt Disclosure [Abstract] Debt Disclosure [Abstract] 3.500% Notes due 2037 3.500% Notes due 2037 [Member] 3.500% Notes due 2037 Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Net amounts, asset Derivative Asset, Subject to Master Netting Arrangement, after Offset Entity Tax Identification Number Entity Tax Identification Number Scenario [Domain] Scenario [Domain] Costs, Expenses and Other Costs and Expenses [Abstract] Tax Reclassification from AOCI, Current Period, Tax Sales based milestone payments Collaborative Arrangement, Rights and Obligations, Milestone Payments, Sales-Based Collaborative Arrangement, Rights and Obligations, Milestone Payments, Sales-Based Asset Acquisition [Axis] Asset Acquisition [Axis] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Axis] Other unallocated, net Segment Reporting Unallocated Other Expenses Net Other net expenses not allocated to segments. Unallocated: Segment Reporting Information, Additional Information [Abstract] Upfront payments recognized as revenue Collaborative Arrangement, Upfront Payments Received Recognized As Revenue Collaborative Arrangement, Upfront Payments Received Recognized As Revenue Inventories Not Expected to be Sold Within One Year Inventory Not Expected to be Sold Within One Year [Member] Inventory Not Expected to be Sold Within One Year [Member] Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest [Member] Restructuring and Related Activities [Abstract] Restructuring and Related Activities [Abstract] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Foreign government bonds Foreign Government Bonds [Member] Foreign Government Bonds Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, issued (in shares) Common stock, beginning balance (in shares) Common stock, ending balance (in shares) Common Stock, Shares, Issued Derivative Asset, Statement of Financial Position [Extensible Enumeration] Derivative Asset, Statement of Financial Position [Extensible Enumeration] Schedule of Income Statement Effects of Derivatives Not Designated as Hedging Instruments Derivatives Not Designated as Hedging Instruments [Table Text Block] Dividends payable Dividends Payable, Current Interest expense Interest expense Interest Expense, Nonoperating Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Loss Contingencies [Line Items] Loss Contingencies [Line Items] Unrealized gains recognized on investments in equity securities without readily determinable fair value Equity Securities without Readily Determinable Fair Value, Upward Price Adjustment, Annual Amount Insider Trading Arrangements [Line Items] Corporate, Non-Segment Other profits Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Security Exchange Name Security Exchange Name Publicly traded equity securities Equity Securities [Member] 4.50% note due 2033 4.50% note due 2033 [Member] 4.50% note due 2033 Other (income) expense, net Other Nonoperating Income (Expense) [Member] 3.85% notes due 2027 3.85% notes due 2027 [Member] 3.85% notes due 2027 Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Accrued and other current liabilities Other Liabilities, Current Share-based compensation plans and other (in shares) Stockholders' Equity, Other Shares Consolidation Items [Axis] Consolidation Items [Axis] Schedule of Charges and Spending Relating to Restructuring Activities by Program Schedule of Restructuring Reserve by Type of Cost [Table Text Block] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Cash and cash equivalents Cash and Cash Equivalent Counterparty Name [Axis] Counterparty Name [Axis] Dr. Falk Pharma Dr. Falk Pharma [Member] Dr. Falk Pharma Patritumab Deruxtecan and Ralduotatug Deruxtecan Patritumab Deruxtecan and Ralduotatug Deruxtecan [Member] Patritumab Deruxtecan and Ralduotatug Deruxtecan Common Stock ($0.50 par value)   Common Stock Common Stock [Member] Debt securities, fair value Commercial paper Debt Securities, Available-for-Sale Stockholders' equity before deduction for treasury stock Stockholders' Equity before Treasury Stock Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Net Increase in Cash, Cash Equivalents and Restricted Cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Common shares issuable (in shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment