Earnings Per Share - Calculations of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Earnings Per Share [Abstract]
Net income attributable to Merck & Co., Inc., basic	$ 17,117	$ 365	$ 14,519
Net income attributable to Merck & Co., Inc., diluted	$ 17,117	$ 365	$ 14,519
Average common shares outstanding (in shares)	2,532	2,537	2,532
Common shares issuable (in shares)	9	10	10
Average common shares outstanding assuming dilution (in shares)	2,541	2,547	2,542
Basic Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 6.76	$ 0.14	$ 5.73
Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 6.74	$ 0.14	$ 5.71