v3.26.1
Master Trust - Schedule of Master Trust Net Assets (Details) - EBP 004 - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
EBP, Master Trust [Line Items]    
    Net assets available for benefits $ 601,546 $ 545,467
Master Trust    
EBP, Master Trust [Line Items]    
Accrued interest and dividends 15,877 17,180
Other net assets 8,648 4,994
    Net assets available for benefits 16,881,531 15,655,880
Master Trust | Registered investment companies (mutual funds)    
EBP, Master Trust [Line Items]    
Investments, at fair value 97,747 500,106
Master Trust | Common/collective trusts    
EBP, Master Trust [Line Items]    
Investments, at fair value 12,677,091 11,107,463
Master Trust | Equity securities    
EBP, Master Trust [Line Items]    
Investments, at fair value 2,307,397 2,244,340
Master Trust | Fixed income securities    
EBP, Master Trust [Line Items]    
Investments, at fair value 406,994 386,182
Master Trust | Self-directed brokerage accounts    
EBP, Master Trust [Line Items]    
Investments, at fair value 459,800 368,784
Master Trust | Merck common stock    
EBP, Master Trust [Line Items]    
Investments, at fair value 907,977 1,026,831
MSD Employee Stock Purchase and Savings Plan Interest    
EBP, Master Trust [Line Items]    
Accrued interest and dividends 829 858
Other net assets 272 177
    Net assets available for benefits 590,023 534,194
MSD Employee Stock Purchase and Savings Plan Interest | Registered investment companies (mutual funds)    
EBP, Master Trust [Line Items]    
Investments, at fair value 4,127 17,600
MSD Employee Stock Purchase and Savings Plan Interest | Common/collective trusts    
EBP, Master Trust [Line Items]    
Investments, at fair value 397,740 336,118
MSD Employee Stock Purchase and Savings Plan Interest | Equity securities    
EBP, Master Trust [Line Items]    
Investments, at fair value 84,643 81,379
MSD Employee Stock Purchase and Savings Plan Interest | Fixed income securities    
EBP, Master Trust [Line Items]    
Investments, at fair value 13,019 11,707
MSD Employee Stock Purchase and Savings Plan Interest | Self-directed brokerage accounts    
EBP, Master Trust [Line Items]    
Investments, at fair value 22,763 15,937
MSD Employee Stock Purchase and Savings Plan Interest | Merck common stock    
EBP, Master Trust [Line Items]    
Investments, at fair value $ 66,630 $ 70,418