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Terns Pharmaceuticals, Inc. Terns Pharmaceuticals, Inc. [Member] Terns Pharmaceuticals, Inc. 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Common Shareholders (in dollars per share) Earnings Per Share, Diluted Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Entity Current Reporting Status Entity Current Reporting Status Collaborative Arrangement, Transaction with Party to Collaborative Arrangement Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member] Net Cash Used in Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Total Shareholder Return Amount Total Shareholder Return Amount Net changes in assets and liabilities Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital Liabilities Liabilities, Fair Value Disclosure [Abstract] Unrealized gain on investments Unrealized Gain (Loss) on Investments Litigation Case [Domain] Litigation Case [Domain] Inventory [Domain] Inventory [Domain] Cumulative amortization expense Intangible Asset, Finite-Lived, Amortization Expense Lynparza Lynparza [Member] Lynparza [Member] Research and development Research and development Research and Development Expense Adjustments to reconcile net (loss) income to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Total current and noncurrent inventories Inventory Net And Inventory Noncurrent Total of current and noncurrent inventories. Stockholders' equity before deduction for treasury stock Stockholders' Equity before Treasury Stock Pretax net unrealized gains 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 Tax Reclassification from AOCI, Current Period, Tax Cash Flows from Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Property, Plant and Equipment, at cost, net of accumulated depreciation of $22,729 in 2026 and $21,914 in 2025 Property, plant and equipment, net Property, Plant, and Equipment, after Accumulated Depreciation, Depletion, and Amortization Peloton Therapeutics, Inc. Peloton Therapeutics, Inc. [Member] Peloton Therapeutics, Inc. Schedule of Equity Schedule of Stockholders Equity [Table Text Block] Interest cost Defined Benefit Plan, Interest Cost Financial Instruments Financial Instruments [Domain] Acquisitions, Research Collaborations and Licensing Agreements Acquisitions Research Collaborations And License Agreements [Text Block] Information related to acquisitions, divestitures, research collaborations and license agreements. Schedule of Charges and Spending Relating to Restructuring Activities by Program Schedule of Restructuring Reserve by Type of Cost [Table Text Block] Fair value of derivative, asset Derivative Asset Inventories Inventory Disclosure [Text Block] Intangible Asset, Finite-Lived, Class [Axis] Intangible Asset, Finite-Lived, Class [Axis] 1.375% Notes due 2036 1.375% Notes due 2036 [Member] 1.375% Notes due 2036 [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Underlying Securities Award Underlying Securities Amount Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Cidara Therapeutics, Inc. Cidara Therapeutics, Inc. [Member] Cidara Therapeutics, Inc. Derivative Asset, Statement of Financial Position [Extensible Enumeration] Derivative Asset, Statement of Financial Position [Extensible Enumeration] Alliance Revenue - Reblozyl Alliance Revenue - Reblozyl [Member] Alliance Revenue - Reblozyl August 2026 Expiration August 2026 Expiration [Member] August 2026 Expiration Financial Instruments Financial Instruments Disclosure [Text Block] Research and development arrangement receivable Other Nontrade Receivable Other Nontrade Receivable Other Payment for (Proceeds from) Other Investing Activity Segment Reporting [Table] Segment Reporting [Table] Ridgeback Biotherapeutics LP Ridgeback Biotherapeutics LP [Member] Ridgeback Biotherapeutics LP Schedule of Information on Investments in Debt and Equity Securities Schedule of Available-for-Sale Securities Reconciliation [Table Text Block] Other current assets Other Assets, Current Sales based royalty percentage Collaborative Arrangement, Rights And Obligations, Royalty Percentage On Sales Collaborative Arrangement, Rights And Obligations, Royalty Percentage On Sales Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] All Trading Arrangements All Trading Arrangements [Member] Amount of gain recognized in Other (income) expense, net on derivatives Derivative, Gain (Loss) on Derivative, Net Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Delayed Draw Term Loan (DDTL) Delayed Draw Term Loan (DDTL) [Member] Total Costs, Expenses and Other Costs Expenses And Other Total of cost of sales, operating expenses and nonoperating income or expense. Asia Pacific (other than China and Japan) Asia Pacific [Member] Current Fiscal Year End Date Current Fiscal Year End Date Proceeds from issuance of debt Proceeds from Issuance of Debt Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Derivative [Line Items] Derivative [Line Items] Royalty rate Royalty Rate, Percentage Royalty Rate, Percentage Capvaxive Capvaxive [Member] Capvaxive Expected restructuring and related cost Restructuring and Related Cost, Expected Cost Restructuring Reserve [Roll Forward] Restructuring Reserve [Roll Forward] 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] Cash dividends declared on common stock (in dollars per share) Common Stock, Dividends, Per Share, Declared Entity File Number Entity File Number Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Service cost Defined Benefit Plan, Service Cost Publicly traded equity securities Equity Securities [Member] (Decrease) increase in Sales as a result of AOCL reclassifications Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Common stock, issued (in shares) Common stock, beginning balance (in shares) Common stock, ending balance (in shares) Common Stock, Shares, Issued Measure: Measure [Axis] Finished goods Inventory, Finished Goods, Gross Entity Information [Line Items] Entity Information [Line Items] Termination benefits Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits Income Tax Estimation, Estimation Expense Type [Axis] Income Tax Estimation, Estimation Expense Type [Axis] Income Tax Estimation, Estimation Expense Type Treasury stock (in shares) Treasury stock, beginning balance (in shares) Treasury stock, ending balance (in shares) Treasury Stock, Common, Shares Other Other Countries [Member] Other Countries [Member] Foreign government bonds Debt Securities, Available-for-Sale, Current Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Equity Components [Axis] Equity Components [Axis] Product and Service [Domain] Product and Service [Domain] Entity Interactive Data Current Entity Interactive Data Current Supplies Other Inventory, Supplies, Gross Less: Net (Loss) Income Attributable to Noncontrolling Interests Net income (loss) attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Deferred Income Taxes Deferred Income Tax Liabilities, Net Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Amount of Derivative Pretax Loss (Gain) Recognized in Income Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Entity Small Business Entity Small Business Comprehensive (Loss) Income Attributable to Merck & Co., Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Termination Date Trading Arrangement Termination Date 5.00% note due 2053 5.00% note due 2053 [Member] 5.00% note due 2053 Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] TARGAN TARGAN [Member] TARGAN Bristol Myers Squibb Company Bristol Myers Squibb Company [Member] Bristol Myers Squibb Company Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Accrued and other current liabilities Other Liabilities, Current Net amounts, asset Derivative Asset, Subject to Master Netting Arrangement, after Offset Other Assets Other Assets, Noncurrent Document Type Document Type Acquisition of Cidara Therapeutics, Inc., net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired 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] Fair Value as of Grant Date Award Grant Date Fair Value Effective income tax rate reconciliation, tax contingency, favorable impact, percent Effective Income Tax Rate Reconciliation, Tax Contingency, Domestic, Percent Loss contingency, number of patents allegedly infringed Loss Contingency, Patents Allegedly Infringed, Number Charges for research and development asset acquisitions Research and Development Asset Acquired in Transaction Other than Business Combination or Joint Venture Formation, Writeoff Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Number of additional patents unpatentable Loss Contingency, Additional Unpatentable Patents , Number Loss Contingency, Additional Unpatentable Patents , Number Arrangement Duration Trading Arrangement Duration Prevymis Prevymis [Member] Prevymis [Member] Verquvo Verquvo [Member] Verquvo Local Phone Number Local Phone Number Other Postretirement Benefit Plans Other Postretirement Benefits Plan [Member] 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. Consolidation Items [Axis] Consolidation Items [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Basis of Presentation Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Ifinatamab Deruxtecan Ifinatamab Deruxtecan [Member] Ifinatamab Deruxtecan Share-based compensation plans and other (in shares) Stockholders' Equity, Other Shares (Loss) Income Before Taxes Pretax loss Other profits Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] 2.500% Notes due 2034 2.500% Notes due 2034 [Member] 2.500% Notes due 2034 [Member] Sales Revenues Debt Instrument, Redemption, Period [Domain] Debt Instrument, Redemption, Period [Domain] Asset under Construction Asset under Construction [Member] Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Equity income from affiliates Income (Loss) from Equity Method Investments Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Executive Category: Executive Category [Axis] China CHINA Counterparty Name [Axis] Counterparty Name [Axis] Liabilities and Equity Liabilities and Equity [Abstract] Intangible Asset, Finite-Lived, Class [Domain] Intangible Asset, Finite-Lived, Class [Domain] Net assets acquired Asset Acquisition, Assets Acquired And Liabilities Assumed, Net Asset Acquisition, Assets Acquired And Liabilities Assumed, Net 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] Inventories (excludes inventories of $6,381 in 2026 and $5,681 in 2025 classified in Other assets - see Note 6) Inventories Inventory, Net All Award Types Award Type [Domain] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Level 3 Fair Value, Inputs, Level 3 [Member] U.S. government and agency securities US Government Agencies Debt Securities [Member] Research and development Research And Development Expense (Reimbursement) Research And Development Expense (Reimbursement) Collaborative arrangement, milestone payment Collaborative Arrangement, Milestone Payment From Collaborative Partner Collaborative Arrangement, Milestone Payment From Collaborative Partner Unrecognized tax benefits Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations Treasury stock shares purchased (in shares) Treasury Stock, Shares, Acquired Foreign Exchange Future Foreign Exchange Future [Member] Koselugo Koselugo [Member] Koselugo Revenue from collaborative arrangement Revenue from Collaborative Arrangement, Excluding Revenue from Contract with Customer PEO Name PEO Name Geographical [Axis] Geographical [Axis] 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 Net periodic defined benefit plan (credit) cost other than service cost Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component Derivatives Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Short-Term Debt [Table] Short-Term Debt [Table] Euro-denominated notes Euro-dominated Notes [Member] Euro-dominated Notes [Member] Long-Lived Asset, Class [Axis] Long-Lived Asset, Class [Axis] Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Entity Tax Identification Number Entity Tax Identification Number 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 Carrying Amount of Hedged Liabilities Hedged Liability, Fair Value Hedge Capitalization of shared costs Prepaid Expense and Other Assets Schedule of Collaboration Arrangements Collaborative Arrangement and Arrangement Other than Collaborative [Table Text Block] U.S. government and agency securities Debt Securities, Available-for-Sale, Noncurrent Treasury stock shares purchased Treasury Stock, Value, Acquired, Cost Method Cumulative unrealized losses on investments Equity Securities without Readily Determinable Fair Value, Downward Price Adjustment, Cumulative Amount (Payments) receipts, net Payments for Restructuring Cash, Cash Equivalents and Restricted Cash at Beginning of Year (includes restricted cash of $125 and $76 at January 1, 2026 and 2025, respectively, included in Other current assets) Cash, Cash Equivalents and Restricted Cash at End of Period (includes restricted cash of $42 and $66 at June 30, 2026 and 2025, respectively, included in Other current assets) Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Cash collateral received, liability Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Not Offset Bridion Bridion [Member] Bridion [Member]. Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Non-NEOs Non-NEOs [Member] 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] Patritumab Deruxtecan Patritumab Deruxtecan [Member] Patritumab Deruxtecan Eisai Eisai [Member] Eisai [Member] Debt Instrument [Axis] Debt Instrument [Axis] Share-based compensation Share-Based Payment Arrangement, Noncash Expense Welireg Welireg [Member] Welireg Loss contingency, regulatory stay duration Loss Contingency, Regulatory Stay Duration Loss Contingency, Regulatory Stay Duration Factored accounts receivable Accounts Receivable, Sale Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] Schedule of Inventory, current Schedule of Inventory, Current [Table Text Block] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Schedule of 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] Basic (Loss) Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share) Earnings Per Share, Basic Purchases of treasury stock Payments for Repurchase of Common Stock Total current assets Other current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Insider Trading Arrangements [Line Items] Schedule of Location and Amount of Pretax Gains and Losses of Derivatives Derivative Instruments, Gain (Loss) [Table Text Block] Long-Term Debt Long-Term Debt, Excluding Current Maturities Award Type Award Type [Axis] Amount of gain (loss) recognized in OCI on derivatives Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax Interest rate contracts Interest Rate Contract [Member] Cumulative Amount of Fair Value Hedging Adjustment Increase Included in the Carrying Amount Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease) Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Pharmaceutical Pharma- ceutical Pharmaceutical segment [Member] Pharmaceutical segment. Accounts receivable (net of allowance for doubtful accounts of $108 in 2026 and $97 in 2025) Accounts Receivable, after Allowance for Credit Loss, Current Income Tax Estimation, Estimation Expense Type [Domain] Income Tax Estimation, Estimation Expense Type [Domain] Income Tax Estimation, Estimation Expense Type [Domain] Retained earnings Retained Earnings (Accumulated Deficit) Restructuring and Related Activities [Abstract] Restructuring and Related Activities [Abstract] Product and Service [Axis] Product and Service [Axis] Net unrealized gain (loss) on derivatives, net of reclassifications Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Parent 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] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Short-Term Debt [Line Items] Short-Term Debt [Line Items] Pension Plans Pension Plan [Member] Common Stock ($0.50 par value)   Common Stock Common Stock [Member] Debt securities, fair value Commercial paper Debt Securities, Available-for-Sale Income Tax Authority, Name [Axis] Income Tax Authority, Name [Axis] Separation Costs Employee Severance [Member] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Cover [Abstract] Cover [Abstract] Vaxneuvance Vaxneuvance [Member] Vaxneuvance Reclassifications Reclassification, Comparability Adjustment [Policy Text Block] Non-US Non-US [Member] 4.95% notes due 2033 4.95% notes due 2033 [Member] 4.95% notes due 2033 5.85% notes due 2056 5.85% notes due 2056 [Member] 5.85% notes due 2056 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 Derivative Contract [Domain] Derivative Contract [Domain] Inventories Produced in Preparation for Product Launches Inventories Produced in Preparation for Product Launches [Member] Inventories Produced in Preparation for Product Launches [Member] Equity Awards Adjustments Equity Awards Adjustments [Member] Collaborative Arrangements Collaborative Arrangement Disclosure [Text Block] Liabilities and Equity Liabilities and Equity Penalties Penalties [Member] Penalties Employee Stock Option Share-Based Payment Arrangement, Option [Member] Loans payable and current portion of long-term debt Debt, Current Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Table] Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Table] Reclassification adjustments, pretax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Noncontrolling Interests Equity, Attributable to Noncontrolling Interest Segments [Axis] Segments [Axis] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] 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] Restructuring costs Restructuring costs Restructuring Charges Inventory Disclosure [Abstract] Inventory Disclosure [Abstract] Gardasil/Gardasil 9 Gardasil/Gardasil 9 [Member] Gardasil/Gardasil 9 [Member]. Tabular List, Table Tabular List [Table Text Block] Companion Animal Companion Animal [Member] Companion Animal [Member] Publicly traded equity securities Equity Securities, FV-NI, Noncurrent Other (income) expense, net Other (income) expense, net Other segment items Other Nonoperating Income (Expense) 3.750% Notes due 2054 3.750% Notes due 2054 [Member] 3.750% Notes due 2054 Name Awards Close in Time to MNPI Disclosures, Individual Name Stockholders Equity [Table] Stockholders Equity [Table] Stockholders Equity [Table] Purchases of securities and other investments Payments to Acquire Investments 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] Long-Lived Asset, Class [Domain] Long-Lived Asset, Class [Domain] Janumet Janumet [Member] Janumet [Member]. Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Unallocated: Segment Reporting, Other Disclosure [Abstract] Adjustment to Compensation: Adjustment to Compensation [Axis] Reclassification adjustments, net of taxes Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Loss contingency, pending claims Loss Contingency, Pending Claims, Number Hedging Designation [Domain] Hedging Designation [Domain] Class of Stock [Domain] Class of Stock [Domain] Zerbaxa Zerbaxa [Member] Zerbaxa [Member] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Dificid Dificid [Member] Dificid Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Hedging Designation [Axis] Hedging Designation [Axis] Inventory [Line Items] Inventory [Line Items] Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Restructuring Restructuring and Related Activities Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Total assets Assets, Fair Value Disclosure Name Measure Name Increase in hedge revenue Increase (Decrease) In Hedge Revenue Increase (Decrease) In Hedge Revenue Income Taxes Income Tax Disclosure [Text Block] Trade accounts payable Accounts Payable, Current Pay vs Performance Disclosure [Line Items] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Other Other Noncash Income (Expense) Accelerated Depreciation Accelerated Depreciation [Member] Accelerated Depreciation [Member] Adempas Adempas [Member] Adempas Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Business combination, consideration transferred Business Combination, Consideration Transferred Other Paid-In Capital Additional Paid-in Capital [Member] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Entity Filer Category Entity Filer Category Alliance revenue - Lynparza Alliance revenue - Lynparza [Member] Alliance revenue - Lynparza [Member] Revenue related to the sale of the marketing rights Proceeds from Sale of Intangible Assets Acquisition of Terns Pharmaceuticals, Inc., net of cash acquired Payments to Acquire Business Two, Net of Cash Acquired Livestock Livestock [Member] Livestock [Member] Payments on term loan Repayments of Short-Term Debt 3.500% Notes due 2037 3.500% Notes due 2037 [Member] 3.500% Notes due 2037 Name Trading Arrangement, Individual Name Currency Swap Currency Swap [Member] Sales based milestone payments Collaborative Arrangement, Rights and Obligations, Milestone Payments, Sales-Based Collaborative Arrangement, Rights and Obligations, Milestone Payments, Sales-Based Cash and cash equivalents Cash and Cash Equivalent Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Axis] Other unallocated, net Segment Reporting Unallocated Other Expenses Net Other net expenses not allocated to segments. 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] Company Selected Measure Amount Company Selected Measure Amount Foreign government bonds Foreign Government Bonds [Member] Foreign Government Bonds Schedule of Reconciliation of Segment Profits to Income before Taxes Segment Reporting, Reconciliation of Profit (Loss) by Segment to Consolidated [Table Text Block] Unrealized net gains (losses) Equity Securities, FV-NI, Unrealized Gain (Loss) Derivatives Not Designated as Hedging Instruments Not Designated as Hedging Instrument [Member] Loans Payable and Long-Term Debt Short-Term Debt [Text Block] Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] Total Inventory, Gross Total return swap contracts Total Return Swap [Member] Net (Loss) Income Net (loss) income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Current Assets Assets, Current [Abstract] Fair value of derivative, liability Derivative Liability Non-PEO NEO Non-PEO NEO [Member] Senior Notes Senior Notes [Member] Entity Address, Address Line One Entity Address, Address Line One Income Tax Provision Income tax provision Income Tax Expense (Benefit) Latin America Latin America [Member] Exchange losses Gain (Loss), Foreign Currency Transaction, before Tax Other (Income) Expense, Net Other Income and Other Expense Disclosure [Text Block] Cost of sales Cost of Product and Service Sold Award Timing Method Award Timing Method [Text Block] 4.50% note due 2033 4.50% note due 2033 [Member] 4.50% note due 2033 Equity Funds Equity Funds [Member] Net Decrease 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 Forecast Forecast [Member] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Derivative liability, notional amount Derivative Liability, Notional Amount Net loss (gain) amortization Defined Benefit Plan, Amortization of Gain (Loss) Accumulated Other Comprehensive Income (Loss) [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Net (Loss) Income Attributable to Merck & Co., Inc. Net (Loss) Income Attributable to Merck & Co., Inc. Net income (loss) attributable to Merck & Co., Inc. Net Income (Loss) Attributable to Parent Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Location, Statement of Financial Position, Balance [Axis] Location, Statement of Financial Position, Balance [Axis] Restatement Determination Date: Restatement Determination Date [Axis] Proceeds from exercise of stock options Proceeds from Stock Options Exercised Schedule of Changes in AOCI by Component Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Interest income Interest income Investment Income, Interest Gross amounts recognized in the consolidated balance sheet, asset Derivative Asset, Subject to Master Netting Arrangement, before Offset Japan JAPAN Amount of Pretax Loss (Gain) Recognized in Other Comprehensive Income Other Comprehensive Income (Loss), Net Investment Hedge, Gain (Loss), before Reclassification and Tax Proceeds from term loan Proceeds from Short-Term Debt Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract]