Cover - shares	3 Months Ended
	Mar. 31, 2026	May 04, 2026
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2026
Document Transition Report	false
Entity File Number	001-42045
Entity Registrant Name	GRAIL, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	86-3673636
Entity Address, Address Line One	1525 O’Brien Drive
Entity Address, City or Town	Menlo Park
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94025
City Area Code	833
Local Phone Number	694-2553
Title of 12(b) Security	Common stock, par value $0.001 per share
Trading Symbol	GRAL
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		42,916,593
Entity Central Index Key	0001699031
Document Fiscal Year Focus	2026
Document Fiscal Period Focus	Q1
Current Fiscal Year End	--12-31
Amendment Flag	false