v3.26.1
Fair Value Measurements (Details) - EBP 004 - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value $ 16,857,006 $ 15,633,706
Fair Value, Inputs, Level 1, Level 2, and Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 4,179,915 4,526,243
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Registered investment companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 97,747 500,106
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Equity securities    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 2,307,397 2,244,340
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Fixed income securities    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 406,994 386,182
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Self-directed brokerage accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 459,800 368,784
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Merck common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 907,977 1,026,831
Quoted Prices In Active Markets for Identical Assets (Level 1)    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 3,772,921 4,140,061
Quoted Prices In Active Markets for Identical Assets (Level 1) | Registered investment companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 97,747 500,106
Quoted Prices In Active Markets for Identical Assets (Level 1) | Equity securities    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 2,307,397 2,244,340
Quoted Prices In Active Markets for Identical Assets (Level 1) | Fixed income securities    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Quoted Prices In Active Markets for Identical Assets (Level 1) | Self-directed brokerage accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 459,800 368,784
Quoted Prices In Active Markets for Identical Assets (Level 1) | Merck common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 907,977 1,026,831
Significant Other Observable Inputs (Level 2)    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 406,994 386,182
Significant Other Observable Inputs (Level 2) | Registered investment companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Equity securities    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Fixed income securities    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 406,994 386,182
Significant Other Observable Inputs (Level 2) | Self-directed brokerage accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Merck common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Significant Unobservable Inputs (Level 3)    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Significant Unobservable Inputs (Level 3) | Registered investment companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Significant Unobservable Inputs (Level 3) | Equity securities    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Significant Unobservable Inputs (Level 3) | Fixed income securities    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Significant Unobservable Inputs (Level 3) | Self-directed brokerage accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
Significant Unobservable Inputs (Level 3) | Merck common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value 0 0
NAV | Common/collective trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Master trust investments at fair value $ 12,677,091 $ 11,107,463