CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($)
$ in Millions
Total
Common Stock and Additional Paid-In Capital
Accumulated Deficit
Beginning balance at Dec. 31, 2016 $ 35 $ 535 $ (500)
Increase (Decrease) in Stockholders' Equity [Roll Forward]      
Issuance of common stock from exercise of stock options   11  
Issuance of common stock for employee stock purchase plan   5  
Stock-based compensation expense   32  
Net income 178   178
Repurchase of common stock     (44)
Awards effectively repurchased for required employee withholding taxes     (11)
Ending balance at Dec. 31, 2017 206 583 (377)
Increase (Decrease) in Stockholders' Equity [Roll Forward]      
Issuance of common stock from exercise of stock options   7  
Issuance of common stock for employee stock purchase plan   7  
Stock-based compensation expense   44  
Net income 192   192
Repurchase of common stock     (61)
Awards effectively repurchased for required employee withholding taxes     (22)
Ending balance at Dec. 31, 2018 375 641 (266)
Increase (Decrease) in Stockholders' Equity [Roll Forward]      
Issuance of common stock from exercise of stock options   2  
Issuance of common stock for employee stock purchase plan   9  
Stock-based compensation expense   42  
Net income 212   212
Repurchase of common stock     (140)
Awards effectively repurchased for required employee withholding taxes     (25)
Ending balance at Dec. 31, 2019 $ 475 $ 694 $ (219)