Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, beginning balance (in shares)	3,577,103,522
Treasury stock, beginning balance (in shares)	1,039,269,638
Equity, beginning balance	$ 46,058	$ 38,257
Net income attributable to Merck & Co., Inc.	2,821	4,310
Other comprehensive income (loss), net of taxes	(115)	60
Cash dividends declared on common stock	(1,863)	(1,754)
Treasury stock shares purchased	(149)
Share-based compensation plans and other	149	83
Net income (loss) attributable to noncontrolling interests	$ 4	(3)
Common stock, ending balance (in shares)	3,577,103,522
Treasury stock, ending balance (in shares)	1,039,651,210
Equity, ending balance	$ 46,905	$ 40,953
Cash dividends declared on common stock (in dollars per share)	$ 0.73	$ 0.69
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, beginning balance (in shares)	3,577,000,000	3,577,000,000
Equity, beginning balance	$ 1,788	$ 1,788
Common stock, ending balance (in shares)	3,577,000,000	3,577,000,000
Equity, ending balance	$ 1,788	$ 1,788
Other Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	44,379	44,238
Share-based compensation plans and other	88	37
Equity, ending balance	44,467	44,275
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	61,081	53,696
Net income attributable to Merck & Co., Inc.	2,821	4,310
Cash dividends declared on common stock	(1,863)	(1,754)
Equity, ending balance	62,039	56,252
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	(4,768)	(4,429)
Other comprehensive income (loss), net of taxes	(115)	60
Equity, ending balance	$ (4,883)	$ (4,369)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock, beginning balance (in shares)	1,039,000,000	1,049,000,000
Equity, beginning balance	$ (56,489)	$ (57,109)
Treasury stock shares purchased (in shares)	1,000,000
Treasury stock shares purchased	$ (149)
Share-based compensation plans and other	$ 61	$ 46
Treasury stock, ending balance (in shares)	1,040,000,000	1,049,000,000
Equity, ending balance	$ (56,577)	$ (57,063)
Non- controlling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	67	73
Net income (loss) attributable to noncontrolling interests	4	(3)
Equity, ending balance	$ 71	$ 70