DESCRIPTION OF BUSINESS AND SIGNIFICANT ACCOUNTING POLICIES - Schedule of Worksite Employee Changes (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Condensed Cash Flow Statements
Accounts receivable, net	$ 1	$ (5)
Payroll funds receivable		0
Prepaid expenses, net	14	(12)
Other assets	(30)	(42)
Other payroll assets	0	3
Accounts payable and other liabilities	0	(10)
Client deposits and other client liabilities	(1)	(9)
Accrued wages	(15)	(23)
Accrued health insurance costs, net	0	(2)
Accrued workers' compensation costs, net	0	(14)
Payroll taxes liabilities and other payroll withholdings	(12)	(8)
Net cash used in operating activities		(122)
Change in WSE and TriNet Trust related assets and liabilities, net	$ (303)	(490)
Net cash used in financing activities		(490)
As previously reported
Condensed Cash Flow Statements
Accounts receivable, net		2
Payroll funds receivable		(64)
Prepaid expenses, net		3
Other assets		(44)
Other payroll assets		(502)
Accounts payable and other liabilities		(13)
Client deposits and other client liabilities		(27)
Accrued wages		52
Accrued health insurance costs, net		18
Accrued workers' compensation costs, net		(19)
Payroll taxes liabilities and other payroll withholdings		(18)
Net cash used in operating activities		(612)
Change in WSE and TriNet Trust related assets and liabilities, net		0
Net cash used in financing activities		0
Reclassified amounts
Condensed Cash Flow Statements
Accounts receivable, net		(7)
Payroll funds receivable		64
Prepaid expenses, net		(15)
Other assets		2
Other payroll assets		505
Accounts payable and other liabilities		3
Client deposits and other client liabilities		18
Accrued wages		(75)
Accrued health insurance costs, net		(20)
Accrued workers' compensation costs, net		5
Payroll taxes liabilities and other payroll withholdings		10
Net cash used in operating activities		490
Change in WSE and TriNet Trust related assets and liabilities, net		(490)
Net cash used in financing activities		$ (490)