STOCK-BASED COMPENSATION - Schedule of ESPP fair value assumptions (Details)	12 Months Ended
Dec. 31, 2025 financialInstitution $ / shares shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected dividend	0.00%
Shares granted (in shares)	2,152,456
Director
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of directors electing to defer cash fees \| financialInstitution	3
Employee Stock \| The GRAIL, Inc. 2024 Employee Stock Purchase Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected life (in years)	6 months
Risk-free interest rate	4.00%
Expected volatility	97.40%
Expected dividend	0.00%
Weighted-average estimated grant date fair value per share (in dollars per share) \| $ / shares	$ 59.31
Performance Shares \| Director
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares granted (in shares)	31,000
Deferred Stock Units \| Director
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares granted (in shares)	30,865

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