v3.26.1
Equity (Details) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Common stock, beginning balance (in shares)     3,577,103,522  
Equity, beginning balance $ 45,931 $ 48,400 $ 52,662 $ 46,372
Treasury stock, beginning balance (in shares)     1,102,476,756  
Net income (loss) attributable to Merck & Co., Inc. (1,335) 4,427 $ (5,575) 9,506
Other comprehensive loss, net of taxes 118 (456) 345 (476)
Cash dividends declared on common stock (2,117) (2,047) (4,231) (4,098)
Treasury stock shares purchased (712) (1,345) (1,637) (2,509)
Share-based compensation plans and other 101 80 425 257
Net income (loss) attributable to noncontrolling interests $ (2) 1 $ (5) 8
Common stock, ending balance (in shares) 3,577,103,522   3,577,103,522  
Equity, ending balance $ 41,984 $ 49,060 $ 41,984 $ 49,060
Treasury stock, ending balance (in shares) 1,108,460,187   1,108,460,187  
Cash dividends declared on common stock (in dollars per share) $ 0.85 $ 0.81 $ 1.70 $ 1.62
  Common Stock        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Common stock, beginning balance (in shares) 3,577,000,000 3,577,000,000 3,577,000,000 3,577,000,000
Equity, beginning balance $ 1,788 $ 1,788 $ 1,788 $ 1,788
Common stock, ending balance (in shares) 3,577,000,000 3,577,000,000 3,577,000,000 3,577,000,000
Equity, ending balance $ 1,788 $ 1,788 $ 1,788 $ 1,788
Other Paid-In Capital        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Equity, beginning balance 45,176 44,816 45,029 44,704
Share-based compensation plans and other (226) (172) (79) (60)
Equity, ending balance 44,950 44,644 44,950 44,644
Retained Earnings        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Equity, beginning balance 66,721 66,097 73,075 63,069
Net income (loss) attributable to Merck & Co., Inc. (1,335) 4,427 (5,575) 9,506
Cash dividends declared on common stock (2,117) (2,047) (4,231) (4,098)
Equity, ending balance 63,269 68,477 63,269 68,477
Accumulated Other Comprehensive Loss        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Equity, beginning balance (4,060) (4,965) (4,287) (4,945)
Other comprehensive loss, net of taxes 118 (456) 345 (476)
Equity, ending balance (3,942) (5,421) (3,942) (5,421)
 Treasury Stock        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Equity, beginning balance $ (63,747) $ (59,401) $ (62,999) $ (58,303)
Treasury stock, beginning balance (in shares) 1,107,000,000 1,061,000,000 1,102,000,000 1,049,000,000
Treasury stock shares purchased (in shares) 6,000,000 17,000,000 14,000,000 29,000,000
Treasury stock shares purchased $ (712) $ (1,345) $ (1,637) $ (2,509)
Share-based compensation plans and other (in shares) (5,000,000) (4,000,000) (8,000,000) (4,000,000)
Share-based compensation plans and other $ 327 $ 251 $ 504 $ 317
Equity, ending balance $ (64,132) $ (60,495) $ (64,132) $ (60,495)
Treasury stock, ending balance (in shares) 1,108,000,000 1,074,000,000 1,108,000,000 1,074,000,000
Non- controlling Interests        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Equity, beginning balance $ 53 $ 65 $ 56 $ 59
Net income (loss) attributable to noncontrolling interests (2) 1 (5) 8
Equity, ending balance $ 51 $ 67 $ 51 $ 67