CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net income	$ 54	$ 29
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	10	8
Stock-based compensation	9	6
Changes in operating assets and liabilities:
Prepaid income taxes	13	15
Prepaid expenses and other current assets	(9)	2
Workers' compensation collateral receivable	(1)	(3)
Other assets	(2)	0
Accounts payable and other current liabilities	(15)	2
Accrued corporate wages	(9)	10
Workers' compensation loss reserves and other non-current liabilities	(6)	8
Worksite employee related assets	(14)	4
Worksite employee related liabilities	(566)	(242)
Net cash used in operating activities	(536)	(161)
Investing activities
Proceeds from maturity of marketable securities	14	4
Acquisitions of property and equipment	(12)	(11)
Net cash provided by (used in) investing activities	2	(7)
Financing activities
Repurchase of common stock	(8)	(28)
Proceeds from issuance of common stock on exercised options	3	2
Awards effectively repurchased for required employee withholding taxes	(4)	(2)
Repayment of notes payable	(10)	(9)
Net cash used in financing activities	(19)	(37)
Net increase (decrease) in cash and cash equivalents, unrestricted and restricted	(553)	(205)
Cash and cash equivalents, unrestricted and restricted:
Beginning of period	1,738	1,233
End of period	1,185	1,028
Supplemental disclosures of cash flow information
Interest paid	4	4
Income taxes paid (refunded), net	0	(1)
Supplemental schedule of noncash investing and financing activities
Payable for purchase of property and equipment	2	2
Supplemental schedule of cash and cash equivalents
Net increase (decrease) in unrestricted cash and cash equivalents	(6)	32
Net increase (decrease) in restricted cash and cash equivalents	$ (547)	$ (237)