Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 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	$ 46,905	$ 40,953	$ 46,058	$ 38,257
Net (loss) income attributable to Merck & Co., Inc.	(5,975)	3,944	(3,154)	8,254
Other comprehensive income (loss), net of taxes	(17)	42	(132)	102
Cash dividends declared on common stock	(1,866)	(1,759)	(3,729)	(3,513)
Treasury stock shares purchased	(338)		(487)
Share-based compensation plans and other	55	133	204	216
Net income attributable to noncontrolling interests	3	5	7	2
Distributions attributable to noncontrolling interests	$ (25)		$ (25)
Common stock, ending balance (in shares)	3,577,103,522		3,577,103,522
Treasury stock, ending balance (in shares)	1,037,678,033		1,037,678,033
Equity, ending balance	$ 38,742	$ 43,318	$ 38,742	$ 43,318
Cash dividends declared on common stock (in dollars per share)	$ 0.73	$ 0.69	$ 1.46	$ 1.38
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	44,467	44,275	44,379	44,238
Share-based compensation plans and other	(248)	(160)	(160)	(123)
Equity, ending balance	44,219	44,115	44,219	44,115
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	62,039	56,252	61,081	53,696
Net (loss) income attributable to Merck & Co., Inc.	(5,975)	3,944	(3,154)	8,254
Cash dividends declared on common stock	(1,866)	(1,759)	(3,729)	(3,513)
Equity, ending balance	54,198	58,437	54,198	58,437
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	(4,883)	(4,369)	(4,768)	(4,429)
Other comprehensive income (loss), net of taxes	(17)	42	(132)	102
Equity, ending balance	$ (4,900)	$ (4,327)	$ (4,900)	$ (4,327)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock, beginning balance (in shares)	1,040,000,000	1,049,000,000	1,039,000,000	1,049,000,000
Equity, beginning balance	$ (56,577)	$ (57,063)	$ (56,489)	$ (57,109)
Treasury stock shares purchased (in shares)	3,000,000		4,000,000
Treasury stock shares purchased	$ (338)		$ (487)
Share-based compensation plans and other (in shares)	(5,000,000)	(5,000,000)	(5,000,000)	(5,000,000)
Share-based compensation plans and other	$ 303	$ 293	$ 364	$ 339
Treasury stock, ending balance (in shares)	1,038,000,000	1,044,000,000	1,038,000,000	1,044,000,000
Equity, ending balance	$ (56,612)	$ (56,770)	$ (56,612)	$ (56,770)
Non- controlling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, beginning balance	71	70	67	73
Net income attributable to noncontrolling interests	3	5	7	2
Distributions attributable to noncontrolling interests	(25)		(25)
Equity, ending balance	$ 49	$ 75	$ 49	$ 75