Earnings Per Share - Calculations of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Income from Continuing Operations Attributable to Merck & Co., Inc.	$ 14,519	$ 12,345	$ 4,519
Income from Discontinued Operations, Net of Taxes and Amounts Attributable to Noncontrolling Interests	0	704	2,548
Net income attributable to Merck & Co., Inc., basic	14,519	13,049	7,067
Net income attributable to Merck & Co., Inc., diluted	$ 14,519	$ 13,049	$ 7,067
Average common shares outstanding (in shares)	2,532	2,530	2,530
Common shares issuable (in shares)	10	8	11
Average common shares outstanding assuming dilution (in shares)	2,542	2,538	2,541
Basic Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders
Income from Continuing Operations (in dollars per share)	$ 5.73	$ 4.88	$ 1.79
Income from Discontinued Operations (in dollars per share)	0	0.28	1.01
Net Income (in dollars per share)	5.73	5.16	2.79
Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders
Income from Continuing Operations (in dollars per share)	5.71	4.86	1.78
Income from Discontinued Operations (in dollars per share)	0	0.28	1.00
Net Income (in dollars per share)	$ 5.71	$ 5.14	$ 2.78