Redeemable Convertible Preferred Stock, Common Stock, and Equity (Deficit) - Summary of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock repurchase cost	$ 0	$ (13)	$ 32
Common Stock
Class of Stock [Line Items]
Common stock shares repurchased (in shares)	1	2,553	11,016
Accumulated Deficit
Class of Stock [Line Items]
Common stock repurchase cost		$ (13)	$ 32
Discrete Arrangement with Employees \| Common Stock
Class of Stock [Line Items]
Common stock shares repurchased (in shares)		286	3,765
Common stock repurchase cost		$ 11	$ 142
Price range per common stock share (in dollars per share)			$ 41.65
Discrete Arrangement with Employees \| Common Stock \| Minimum
Class of Stock [Line Items]
Price range per common stock share (in dollars per share)		$ 36.58	$ 5.00
Discrete Arrangement with Employees \| Common Stock \| Maximum
Class of Stock [Line Items]
Price range per common stock share (in dollars per share)		$ 41.65
Discrete Arrangement with Employees \| Accumulated Deficit
Class of Stock [Line Items]
Common stock repurchase cost		$ 13	$ 32
Discrete Arrangement with Employees \| Additional Paid-In Capital
Class of Stock [Line Items]
Common stock repurchase cost		$ 1	$ 13