Factored accounts receivable Accounts Receivable, Sale Statistical Measurement [Domain] Statistical Measurement [Domain] Other current assets Other Current Assets [Member] Daiichi Sankyo Daiichi Sankyo [Member] Daiichi Sankyo Settled Litigation Settled Litigation [Member] Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets International Foreign Plan [Member] Restricted cash Restricted Cash, Current Award Timing Predetermined Award Timing Predetermined [Flag] Future regulatory milestone payments (up to) Asset Acquisition, Maximum Aggregate Regulatory Milestone Payments Asset Acquisition, Maximum Aggregate Regulatory Milestone Payments Delstrigo Delstrigo [Member] Delstrigo Collaborative Arrangements [Abstract] Collaborative Arrangements [Abstract] Collaborative Arrangements [Abstract] Entity File Number Entity File Number Other Paid-In Capital Additional Paid-in Capital [Member] Interest rate swap contracts Interest Rate Swap [Member] Aggregate upfront payments due upon execution in collaborative arrangement Collaborative Arrangement, Rights And Obligations, Aggregate Upfront Payments Due Upon Execution Collaborative Arrangement, Rights And Obligations, Aggregate Upfront Payments Due Upon Execution Equity income from affiliates Income (Loss) from Equity Method Investments Other (Income) Expense, Net Other Income and Other Expense Disclosure [Text Block] Tabular List, Table Tabular List [Table Text Block] Recently Issued Accounting Standards Not Yet Adopted New Accounting Pronouncements, Policy [Policy Text Block] 3.250% Notes due 2032 3.250% Notes due 2032 [Member] 3.250% Notes due 2032 Type of Restructuring [Domain] Type of Restructuring [Domain] Debt securities, unrealized losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Future contingent developmental milestone payments (up to) Asset Acquisition, Maximum Aggregate Contingent Development-Related Payments Asset Acquisition, Maximum Aggregate Contingent Development-Related Payments Basic Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share) Earnings Per Share, Basic Adjustment to Compensation: Adjustment to Compensation [Axis] Amount of Pretax Loss (Gain) Recognized in Other Comprehensive Income Other Comprehensive Income (Loss), Net Investment Hedge, Gain (Loss), before Reclassification and Tax Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Total Inventory, Gross Commercial paper Commercial Paper [Member] Liabilities Liabilities, Fair Value Disclosure [Abstract] Lagevrio Lagevrio [Member] Lagevrio Collaboration Arrangements Collaborative Arrangement and Arrangement Other than Collaborative [Table Text Block] Jiangsu Hengrui Pharmaceuticals Co., Ltd. Jiangsu Hengrui Pharmaceuticals Co., Ltd. [Member] Jiangsu Hengrui Pharmaceuticals Co., Ltd. Other comprehensive loss, net of taxes Other comprehensive income (loss), net of taxes Other Comprehensive Income (Loss), Net of Tax Equity Loss from Affiliates and Depreciation Included in Segment Profits Schedule of Segment Reporting Information, by Segment [Table Text Block] Inventory Disclosure [Abstract] Inventory Disclosure [Abstract] Supplies Other Inventory, Supplies, Gross Patent extension, term Patent Extension, Term Patent Extension, Term Information on Investments in Debt and Equity Securities Schedule of Available-for-Sale Securities Reconciliation [Table Text Block] Adjustment to Compensation, Amount Adjustment to Compensation Amount Revenue from collaborative arrangement Revenue from Collaborative Arrangement, Excluding Revenue from Contract with Customer Pension Plans Pension Plan [Member] Loss contingency, number of cases remanded Loss Contingency, Number Of Cases Remanded Loss Contingency, Number Of Cases Remanded 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 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] Patents Patents [Member] Current Assets Assets, Current [Abstract] Liabilities and Equity Liabilities and Equity Fair Value, Measurements, Recurring Fair Value, Recurring [Member] Employee Benefit Plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Table] Licensing Agreements Licensing Agreements [Member] Estimate of cumulative pre tax costs that will be cash Restructuring and Related Cost, Expected Pretax Costs, Cash Percentage Restructuring and Related Cost, Expected Pretax Costs, Cash Percentage Liabilities and Equity Liabilities and Equity [Abstract] Cover [Abstract] Cover [Abstract] Total pretax restructuring costs Expenses Restructuring and Related Cost, Incurred Cost Maximum Maximum [Member] Legal Defense Costs Legal Defense Costs [Member] Legal Defense Costs [Member] Estimate of cumulative pre tax costs that will be noncash Restructuring and Related Cost, Expected Pretax Costs, Non-Cash Percentage Restructuring and Related Cost, Expected Pretax Costs, Non-Cash Percentage Less: Net Income Attributable to Noncontrolling Interests Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Finite-lived intangible assets Finite-Lived Intangible Assets, Net Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Net periodic defined benefit plan (credit) cost other than service cost Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component  Treasury Stock Treasury Stock, Common [Member] Sales discounts Sales Discounts Sales Discounts Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Debt, carrying amount Debt, Long-Term and Short-Term, Combined Amount U.S. government and agency securities US Government Agencies Debt Securities [Member] Unrealized losses recognized on investments in equity securities without readily determinable fair values Equity Securities without Readily Determinable Fair Value, Downward Price Adjustment, Annual Amount Retirement Benefits [Abstract] Retirement Benefits [Abstract] AstraZeneca AstraZeneca [Member] AstraZeneca [Member] Cumulative translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Other Assets Other Assets [Member] Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Income Before Taxes Total segment profits Other profits Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Other Noncurrent Liabilities Other Liabilities, Noncurrent 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 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 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 Sales based royalty percentage Collaborative Arrangement, Rights And Obligations, Royalty Percentage Collaborative Arrangement, Rights And Obligations, Royalty Percentage 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 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] 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] Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Januvia Januvia [Member] Januvia [Member] . Motion for Summary Judgement Granted Motion for Summary Judgement Granted [Member] Motion for Summary Judgement Granted PEO PEO [Member] Loss contingency, pending claims Loss Contingency, Pending Claims, Number Separation Costs Employee Severance [Member] Internal Revenue Service (IRS) Internal Revenue Service (IRS) [Member] Interest income Interest income Investment Income, Interest Income taxes payable Accrued Income Taxes, Current U.S. United States UNITED STATES Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Property, Plant and Equipment, Net by Geographic Area Schedule of Disclosure on Geographic Areas, Long-Lived Assets in Individual Foreign Countries by Country [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract] Retained Earnings Retained Earnings [Member] Upfront cash payment Proceeds From Upfront Payment, Cash Proceeds From Upfront Payment, Cash Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Cash, Cash Equivalents and Restricted Cash at Beginning of Year (includes restricted cash of $76 and $68 at January 1, 2025 and 2024, respectively, included in Other current assets) Cash, Cash Equivalents and Restricted Cash at End of Period (includes restricted cash of $66 and $69 at June 30, 2025 and 2024, respectively, included in Other current assets) Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income Statement [Abstract] Fair value of derivative, asset Derivative Asset Taxes on Income Income Tax Expense (Benefit) Aggregate upfront payments due upon lapse of time in collaborative arrangement Collaborative Arrangement, Rights And Obligations, Aggregate Upfront Payments Due Upon Lapse Of Time Collaborative Arrangement, Rights And Obligations, Aggregate Upfront Payments Due Upon Lapse Of Time RotaTeq Rotateq [Member] RotaTeq [Member] Other Intangibles, Net Intangible Assets, Net (Excluding Goodwill) Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Derivatives Designated as Hedging Instruments Designated as Hedging Instrument [Member] Product and Service [Domain] Product and Service [Domain] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Consideration transferred, asset acquisition (in dollars per depository share) Asset Acquisition, Consideration Transferred, Amount Per American Depository Share Asset Acquisition, Consideration Transferred, Amount Per American Depository Share Net Income Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Total liabilities Liabilities, Fair Value Disclosure Business Combination [Table] Business Combination [Table] Restructuring Program, 2024 Restructuring Program, 2024 [Member] Restructuring Program, 2024 Derivative, notional amount U.S dollar notional amount U.S dollar notional amount Derivative, Notional Amount Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Other pharmaceutical Other Pharmaceutical [Member] Other pharmaceutical. Patents - PGR Petition PGR Petition [Member] PGR Petition Other Income and Expenses [Abstract] Other Income and Expenses [Abstract] Restructuring Restructuring and Related Activities Disclosure [Text Block] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Maximum aggregate sales-based milestone payments Asset Acquisition, Maximum Aggregate Sales-Based Milestone Payments Asset Acquisition, Maximum Aggregate Sales-Based Milestone Payments Proceeds from exercise of stock options Proceeds from Stock Options Exercised Tax benefit resulting from acquisition charge Tax Benefit Resulting From Acquisition Charge Tax Benefit Resulting From Acquisition Charge City Area Code City Area Code Acquisition of Harpoon Therapeutics, Inc., net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Payments Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Foreign Exchange Future Foreign Exchange Future [Member] Belsomra Belsomra [Member] Belsomra [Member] Pneumovax 23 Pneumovax 23 [Member] Pneumovax 23[Member]. Cash Flows from Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Net Cash Provided by Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] Alliance revenue - Lenvima Lenvima [Member] Lenvima [Member] Maximum aggregate contingent milestone payments, per product, in collaborative arrangement Collaborative Arrangement, Rights And Obligations, Maximum Aggregate Contingent Milestone Payments, Per Product Collaborative Arrangement, Rights And Obligations, Maximum Aggregate Contingent Milestone Payments, Per Product Income tax examination, estimate of possible loss Income Tax Examination, Estimate of Possible Loss Revenues from External Customers and Long-Lived Assets [Line Items] Revenues from External Customers and Long-Lived Assets [Line Items] Net (gain) loss amortization Defined Benefit Plan, Amortization of Gain (Loss) Subsequent Event Subsequent Event [Member] Selling, general and administrative Selling, General and Administrative Expenses [Member] Cost of sales Cost of Sales [Member] Goodwill Goodwill Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Depreciation Depreciation Depreciation Gross amounts recognized in the consolidated balance sheet, liability Derivative Liability, Subject to Master Netting Arrangement, before Offset Dr. Scholl's Dr. Scholl's [Member] Dr. Scholl's Equity Components [Axis] Equity Components [Axis] Non-US Non-US [Member] 1.875% Notes due 2026 1.875% Notes due 2026 [Member] 1.875% Notes due 2026 [Member] Stockholders Equity [Line Items] Stockholders Equity [Line Items] [Line Items] for Stockholders Equity [Table] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Sales Sales [Member] Basis of Presentation Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost Revenue from External Customer [Line Items] Revenue from External Customer [Line Items] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Other Performance Measure, Amount Other Performance Measure, Amount Inventory [Line Items] Inventory [Line Items] Loans payable and current portion of long-term debt Debt, Current Entity Address, State or Province Entity Address, State or Province Pretax net unrealized loss on derivatives maturing within the next 12 months estimated to be reclassified from AOCI to sales Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months Isentress/Isentress HD Isentress/Isentress HD [Member] Isentress/Isentress HD [Member]. Raw materials and work in process Inventory, Work in Process and Raw Materials, Excluding Supplies Inventory, Work in Process and Raw Materials, Excluding Supplies Total current liabilities Liabilities, Current Accrued and other current liabilities Other Current Liabilities [Member] Pifeltro Pifeltro [Member] Pifeltro Inventory [Axis] Inventory [Axis] Income from investments in equity securities, net Loss (income) from investments in equity securities, net Equity Securities, FV-NI, Gain (Loss) Litigation Status [Axis] Litigation Status [Axis] Derivative Instrument [Axis] Derivative Instrument [Axis] Cumulative costs since program inception Restructuring and Related Cost, Cost Incurred to Date Individual: Individual [Axis] Inventory [Table] Inventory [Table] Inventory [Table] Dividends paid to stockholders Payments of Ordinary Dividends, Common Stock Other current assets Other Assets, Current Research and development Research and Development Expense [Member] Licenses and Other Licenses and Other [Member] Licenses and Other Other paid-in capital Additional Paid in Capital, Common Stock Entities [Table] Entities [Table] Cumulative unrealized losses on investments Equity Securities without Readily Determinable Fair Value, Downward Price Adjustment, Cumulative Amount Other Exit Costs Other Restructuring [Member] Net Cash Used in Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Amortization Amortization Amortization Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity 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 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. Equity [Abstract] Equity [Abstract] Legal defense costs reserve Estimated Litigation Liability Cumulative unrealized gains on investments Equity Securities without Readily Determinable Fair Value, Upward Price Adjustment, Cumulative Amount Less segment costs: Segment Reconciliation [Abstract] Segment Reporting Segment Reporting Disclosure [Text Block] Financial Assets and Liabilities Measured at Fair Value on Recurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Derivatives Not Designated as Hedging Instruments Not Designated as Hedging Instrument [Member] Latin America Latin America [Member] Raludotatug Deruxtecan Raludotatug Deruxtecan [Member] Raludotatug Deruxtecan Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset [Axis] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Axis] Securities subject to contractual sale restrictions Equity Security, FV-NI, Contractual Sale Restriction Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Investments Marketable Securities, Noncurrent Net unrealized (loss) gain on derivatives, net of reclassifications Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Parent Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Contingent consideration Fair value, beginning balance Fair value, ending balance Business Combination, Contingent Consideration, Liability WuXi Vaccines' facility WuXi Vaccines' facility [Member] WuXi Vaccines' facility Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Winrevair Winrevair [Member] Winrevair Selling, general and administrative Selling, General and Administrative Expense Schedule of Changes in AOCI by Component Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Other Assets Other Assets Other Assets, Noncurrent Loss contingency, joint stipulation response period Loss Contingency, Joint Stipulation Response Period Loss Contingency, Joint Stipulation Response Period Entity Central Index Key Entity Central Index Key PEO Name PEO Name Schedule of Revenues from External Customers and Long-Lived Assets [Table] Schedule of Revenues from External Customers and Long-Lived Assets [Table] Sales Revenues Amount of Derivative Pretax (Gain) Loss Recognized in Income Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Finished goods Inventory, Finished Goods, Gross Currency Swap Currency Swap [Member] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Schedule of Equity Schedule of Stockholders Equity [Table Text Block] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plan [Table] Arrangement Duration Trading Arrangement Duration Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Financial Instruments Financial Instruments Disclosure [Text Block] Segments [Axis] Segments [Axis] 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 Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] ProQuad/M-M-R II/Varivax ProQuad MMR II Varivax [Member] ProQuad/M-M-R II/Varivax [Member]. 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] 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 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. 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) Other (Income) Expense, Net Schedule of Other Nonoperating Income (Expense) [Table Text Block] Keytruda Keytruda [Member] Keytruda [Member] 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 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] Non-PEO NEO Non-PEO NEO [Member] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] 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 Summary 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 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 (loss) gain 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) 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 Debt Instrument, Face Amount 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] 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 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 $4,882 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 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 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. 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 Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Derivative [Table] Derivative [Table] 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 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 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] 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 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] Eligible future contingent sales-based milestone payments (up to) 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] 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 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] 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 loss and prior service 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] Eligible future contingent regulatory milestone payments (up to) 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 $94 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] 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 Asset acquisition, share conversion, ordinary shares per depository shares (in shares) Asset Acquisition, Share Conversion, Ordinary Shares Per Depository Shares Asset Acquisition, Share Conversion, Ordinary Shares Per Depository Shares 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] 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 Global minimum tax impact on effective tax rate, percentage increase Effective Income Tax Rate Reconciliation, Global Minimum Tax Impact, Increase (Decreae) Effective Income Tax Rate Reconciliation, Global Minimum Tax Impact, Increase (Decreae) 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] 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 Charge for research and development asset acquisition Research and Development Asset Acquired in Transaction Other than Business Combination or Joint Venture Formation, Writeoff Pharmaceutical Pharma- ceutical Pharmaceutical segment [Member] Pharmaceutical segment. 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] 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] Unrealized net gains (losses) Equity Securities, FV-NI, Unrealized Gain (Loss) Property, Plant and Equipment, at cost, net of accumulated depreciation of $20,256 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 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 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] Income tax rate, unfavorable discrete impact Effective Income Tax Rate Reconciliation, Nondeductible Expense, Research and Development, Percent 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 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: 1,073,963,194 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 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] 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] 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] 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] 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] 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] 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] 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 (Decrease) 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