ACCRUED WORKERS' COMPENSATION COSTS - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Insurance [Abstract]
Collateral held by insurance carriers	$ 25	$ 26
Collateral paid to carriers and offset against loss reserves	$ 4	$ 4

Liability for Unpaid Claims and Claims Adjustment Expense, Collateral

No definition available.

Name:	tnet_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseCollateral
Namespace Prefix:	tnet_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant