CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Millions	Total	Common Stock and Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income
Beginning balance at Dec. 31, 2021	$ 881	$ 808	$ 74	$ (1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercise of stock options		1
Issuance of common stock for employee stock purchase plan		5
Issuance of common stock for the acquisition of Zenefits		17
Stock based compensation expense		47
Net income	307		307
Repurchase of common stock			(383)
Stock repurchase excise tax			0
Awards effectively repurchased for required employee withholding taxes			(15)
Other comprehensive income (loss)	(4)			(4)
Ending balance at Sep. 30, 2022	856	878	(17)	(5)
Beginning balance at Jun. 30, 2022	763	861	(86)	(12)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercise of stock options		0
Issuance of common stock for employee stock purchase plan		0
Issuance of common stock for the acquisition of Zenefits		0
Stock based compensation expense		17
Net income	77		77
Repurchase of common stock			(1)
Stock repurchase excise tax			0
Awards effectively repurchased for required employee withholding taxes			(7)
Other comprehensive income (loss)	7			7
Ending balance at Sep. 30, 2022	856	878	(17)	(5)
Beginning balance at Dec. 31, 2022	775	899	(120)	(5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercise of stock options		3
Issuance of common stock for employee stock purchase plan		6
Issuance of common stock for the acquisition of Zenefits		0
Stock based compensation expense		45
Net income	308		308
Repurchase of common stock			(1,102)
Stock repurchase excise tax			(7)
Awards effectively repurchased for required employee withholding taxes			(14)
Other comprehensive income (loss)	(3)			(3)
Ending balance at Sep. 30, 2023	10	953	(935)	(8)
Beginning balance at Jun. 30, 2023	915	934	(13)	(6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercise of stock options		3
Issuance of common stock for employee stock purchase plan		0
Issuance of common stock for the acquisition of Zenefits		0
Stock based compensation expense		16
Net income	94		94
Repurchase of common stock			(1,004)
Stock repurchase excise tax			(7)
Awards effectively repurchased for required employee withholding taxes			(5)
Other comprehensive income (loss)	(2)			(2)
Ending balance at Sep. 30, 2023	$ 10	$ 953	$ (935)	$ (8)