Accrued Workers' Compensation Cost - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Insurance [Abstract]
Collateral held by insurance carriers	$ 45	$ 46
Liability for unpaid claims and claims adjustment expense, collateral	$ 9	$ 9

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