Sale of common stock EBP, Investment Sold, Plan Interest in Master Trust, Selling Price Investments, at fair value EBP, Investment, Fair Value Entity tax identification number Entity Tax Identification Number Maximum Maximum [Member] Legal Entity [Axis] Legal Entity [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] EBP, Description of Plan [Table] EBP, Description of Plan [Table] Registered investment companies (mutual funds) Registered investment companies Mutual Fund [Member] EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Table] Participant contribution, pretax, maximum annual compensation to total compensation, percentage EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, Percentage Self-directed brokerage accounts EBP, Self-Directed Brokerage Account [Member] Receivable from participant, account, maximum borrowing, amount EBP, Note Receivable from Participant, Account, Maximum Borrowing, Amount Fair Value Measurements EBP, Investment, Fair Value and NAV [Text Block] Receivable from participant, account, minimum borrowing, amount EBP, Note Receivable from Participant, Account, Minimum Borrowing, Amount Employer contribution, matching percentage per US dollar EBP, Employer Contribution, Matching Percentage Per US Dollar EBP, Employer Contribution, Matching Percentage Per US Dollar Fixed income securities Fixed Income Securities [Member] Short term loan, borrowing term EBP, Note Receivable From Participant, Short Term Loan, Borrowing Term EBP, Note Receivable From Participant, Short Term Loan, Borrowing Term         Investment in Master Trust, at fair value EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value MSD Employee Stock Purchase and Savings Plan Interest EBP, Nonconsolidated, Plan Interest in Master Trust [Member] Quoted Prices In Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] EBP, Investment, Fair Value and NAV [Abstract] Assets EBP, Asset [Abstract] Statistical Measurement [Axis] Statistical Measurement [Axis] Additions to net assets attributed to EBP, Change in Net Asset Available for Benefit, Increase [Abstract] EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Table] Payment of Benefits EBP, Payment to Participant [Policy Text Block] Trustee EBP, Trustee [Member] EBP, Master Trust [Line Items] EBP, Master Trust [Line Items] Master trust, current value EBP, Asset Held for Investment, Plan Interest in Master Trust, Current Value Amendment Flag Amendment Flag         By participants EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution Basis of Accounting EBP, Basis of Accounting [Policy Text Block] EBP, Schedule of Asset Held for Investment [Table] EBP, Schedule of Asset Held for Investment [Table]         Investment in Master Trust, at fair value EBP, Investment, Plan Interest in Master Trust, Fair and Contract Value EBP, Description of Plan and Accounting Change [Abstract]     Receivables EBP, Receivable [Abstract] Schedule of master trust investments measured at fair value EBP, Investment, Fair Value and NAV [Table Text Block] Investments [Domain] Investments [Domain] EBP, Master Trust [Abstract] Use of Estimates EBP, Use of Estimate [Policy Text Block] EBP, Related Party and Party-in-Interest [Domain] EBP, Related Party and Party-in-Interest [Domain] Schedule H, Line 4i – Schedule of Assets (Held At End of Year) EBP, Schedule of Asset Held for Investment [Text Block] Cover [Abstract]         By employer EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash Accrued interest and dividends EBP, Investment Income, Receivable Purchase price EBP, Investment Acquired, Plan Interest in Master Trust, Purchase Price EBP, Related Party and Party-in-Interest [Axis] EBP, Related Party and Party-in-Interest [Axis] Minimum Minimum [Member] Minimum annual compensation to total compensation, percentage EBP, Participant Contribution, Pretax, Minimum Annual Compensation to Total Compensation, Percentage EBP, Participant Contribution, Pretax, Minimum Annual Compensation to Total Compensation, Percentage Investment Type [Axis] Investment Type [Axis]     Interest income on notes receivable from participants EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Note Receivable from Participant             Total contributions EBP, Change in Net Asset Available for Benefit, Increase from Contribution     Transfers out EBP, Change In Net Asset Available For Benefit, Transfer From EBP, Change In Net Asset Available For Benefit, Transfer From         Plan interest in Master Trust investment gain     Net appreciation EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment     Interest and dividends EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment EBP, Description of Plan [Line Items] EBP, Description of Plan [Line Items] Plan number EBP, Plan Number EBP, Investment, Fair Value and NAV [Line Items] EBP, Investment, Fair Value and NAV [Line Items] Description of Plan EBP, Description of Plan [Text Block] Basis spread on variable rate EBP, Participant Loan, Basis Spread On Variable Rate EBP, Participant Loan, Basis Spread On Variable Rate EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Schedule of Asset Held for Investment [Line Items] EBP, Schedule of Asset Held for Investment [Line Items] Contributions EBP, Contribution [Policy Text Block] EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Domain] EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Domain] Merck common stock EBP, Employer, Common Stock [Member] EBP, Schedule of Asset Held for Investment [Abstract] EBP, Accounting Policy [Table] EBP, Accounting Policy [Table] Participant contribution, aftertax, maximum annual compensation to total compensation, percentage EBP, Participant Contribution, Aftertax, Maximum Annual Compensation to Total Compensation, Percentage EBP, Participant Contribution, Aftertax, Maximum Annual Compensation to Total Compensation, Percentage     Investment gain EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract] Administrative expenses EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense Total current value EBP, Asset Held for Investment Risks and Uncertainties EBP, Risk and Uncertainty [Policy Text Block] Document Information [Line Items] Document Information [Line Items] Master Trust EBP, Master Trust [Text Block] Realized gain on investment EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Realized Gain (Loss) on Investment Employer contribution, participant compensation matched, percentage EBP, Employer Contribution, Participant Compensation Matched, Percentage EBP, Statement of Change in Net Asset Available for Benefit [Abstract] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Receivable from participant, account, primary residence, maximum borrowing term EBP, Note Receivable From Participant, Account, Primary Residence, Maximum Borrowing Term EBP, Note Receivable From Participant, Account, Primary Residence, Maximum Borrowing Term Equity securities Equity Securities [Member]             Net increase EBP, Change in Net Asset Available for Benefit, Increase (Decrease) and Transfers To (From) Plan EBP, Change in Net Asset Available for Benefit, Increase (Decrease) and Transfers To (From) Plan EBP, Tax Status [Table] EBP, Tax Status [Table] Related-Party Transactions EBP, Related Party and Party-in-Interest Transactions [Text Block] EBP, Related Party and Party-in-Interest Transactions [Abstract] EBP, Accounting Policy, Accounting Standard Update, and Change in Accounting Principle [Abstract]             Total receivables EBP, Receivable         Employer contributions EBP, Employer Contribution, Receivable Unrealized gain on investment EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Unrealized Gain (Loss) on Investment     Investments EBP, Investment, Fair Value [Abstract] Increase from dividend income on investment EBP, Change in Net Asset Available for Benefit, Increase from Dividend Income on Investment Participant withdrawals EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Master trust investments at fair value EBP, Investment, Plan Interest in Master Trust, Fair Value             Total additions EBP, Change in Net Asset Available for Benefit, Increase and Transfer To Plan EBP, Change in Net Asset Available for Benefit, Increase and Transfer To Plan Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] EBP, Statement of Net Asset Available for Benefit [Abstract] EBP, Accounting Policy [Line Items] EBP, Accounting Policy [Line Items] EBP, Tax Status [Abstract] Administrative Expenses EBP, Expense [Policy Text Block] Notes receivable from participants, current value EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution Investment Valuation and Income Recognition EBP, Investment [Policy Text Block] EBP, Master Trust [Table] EBP, Master Trust [Table]         Participant contributions EBP, Participant Contribution, Receivable Fair Value, Inputs, Level 1, Level 2, and Level 3 Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] Document Type Document Type Participant contribution, maximum contribution to eligible compensation, percentage EBP, Participant Contribution, Maximum Contribution to Eligible Compensation, Percentage EBP, Participant Contribution, Maximum Contribution to Eligible Compensation, Percentage Plan Termination EBP, Plan Termination [Text Block] Entity Central Index Key Entity Central Index Key Notes receivable from participants, interest rate EBP, Asset Held for Investment, Participant Loan, Interest Rate Common/collective trusts Common Collective Trust [Member] Net assets available for benefits EBP, Net Asset Available for Benefit [Abstract] EBP, Tax Status [Line Items] EBP, Tax Status [Line Items] EBP, Subsequent Event [Table] EBP, Subsequent Event [Table] Deductions from net assets attributed to EBP, Change in Net Asset Available for Benefit, Decrease [Abstract]         Notes receivable from participants EBP, Note Receivable from Participant Master Trust EBP, Nonconsolidated, Master Trust [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Other net assets EBP, Other Asset Summary of Accounting Policies EBP, Summary of Accounting Policy [Text Block] Entity Registrant Name Entity Registrant Name Schedule of master trust net assets EBP, Master Trust [Table Text Block] EBP, Subsequent Event [Abstract] Subsequent Events EBP, Subsequent Event [Text Block] Tax Status EBP, Tax Status [Text Block]     Transfers in EBP, Change In Net Asset Available For Benefit, Transfer To EBP, Change In Net Asset Available For Benefit, Transfer To Note receivable from participant, account, maximum borrowing, to total account, percentage EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage EBP, Subsequent Event [Line Items] EBP, Subsequent Event [Line Items] Document Information [Table] Document Information [Table] EBP 004 EBP 004 [Member] EBP 004 Notes Receivable from Participants EBP, Note Receivable from Participant [Policy Text Block]         Total investment income EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Axis] EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Axis]             Total deductions EBP, Change in Net Asset Available for Benefit, Decrease and Transfers From Plan EBP, Change in Net Asset Available for Benefit, Decrease and Transfers From Plan EBP, Related Party and Party-in-Interest Transactions [Line Items] EBP, Related Party and Party-in-Interest Transactions [Line Items] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member]     Net assets available for benefits     Beginning of year     End of year EBP, Net Asset Available for Benefit Entity [Domain] Entity [Domain]     Contributions to the Plan EBP, Change in Net Asset Available for Benefit, Increase from Contribution [Abstract] Employer contribution, matching percentage EBP, Employer Contribution, Matching Percentage NAV Fair Value Measured at Net Asset Value Per Share [Member] EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Table] EBP, Statement of Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Line Items]