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, 2019	$ 475	$ 694	$ (219)	$ 0
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		5
Stock based compensation expense		31
Net income	250		250
Repurchase of common stock			(135)
Awards effectively repurchased for required employee withholding taxes			(11)
Other comprehensive (loss) income	4			5
Ending balance at Sep. 30, 2020	620	730	(115)	5
Beginning balance at Jun. 30, 2020	616	719	(108)	5
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
Stock based compensation expense		11
Net income	33		33
Repurchase of common stock			(35)
Awards effectively repurchased for required employee withholding taxes			(5)
Other comprehensive (loss) income	0			0
Ending balance at Sep. 30, 2020	620	730	(115)	5
Beginning balance at Dec. 31, 2020	607	747	(144)	4
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
Stock based compensation expense		37
Net income	269		269
Repurchase of common stock	(94)		(94)
Awards effectively repurchased for required employee withholding taxes			(13)
Other comprehensive (loss) income	(3)
Ending balance at Sep. 30, 2021	809	790	18	1
Beginning balance at Jun. 30, 2021	744	776	(35)	3
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		0
Stock based compensation expense		13
Net income	77		77
Repurchase of common stock			(20)
Awards effectively repurchased for required employee withholding taxes			(4)
Other comprehensive (loss) income	(2)
Ending balance at Sep. 30, 2021	$ 809	$ 790	$ 18	$ 1