Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2022	Feb. 17, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-36407
Entity Registrant Name	ALNYLAM PHARMACEUTICALS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	77-0602661
Entity Address, Address Line One	675 West Kendall Street
Entity Address, Address Line Two	Henri A. Termeer Square
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	551-8200
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol	ALNY
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 17,596,044,220
Entity Common Stock, Shares Outstanding		124,130,988
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement for its 2023 annual meeting of stockholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of December 31, 2022, are incorporated by reference into Part II, Item 5 and Part III of this Form 10-K.
Amendment Flag	false
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Entity Central Index Key	0001178670