STOCK-BASED COMPENSATION - 2024 Incentive award plan (Details) - The GRAIL, Inc. 2024 Incentive Award Plan - shares	Sep. 30, 2024	May 31, 2024
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares available for grant (in shares)	2,400,000	8,656,817
Annual increase in shares available for grant as a percentage		5.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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