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STOCK-BASED COMPENSATION - 2024 ESPP (Details) - Employee Stock - The GRAIL, Inc. 2024 Employee Stock Purchase Plan
12 Months Ended
Dec. 31, 2025
May 31, 2024
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]    
Annual increase in shares available for grant as a percentage   1.00%
Maximum earnings withheld for purchase of shares (as a percent) 15.00%  
Purchase price as a percentage of fair value (as a percent) 85.00%