Condensed Consolidated Statement of Redeemable Equity $ in Millions	USD ($)
Beginning Balance at Dec. 31, 2017	$ 36
Share-based Payments Subject to Redemption
Share-based compensation, net of issuance	(9)
Ending Balance at Mar. 31, 2018	27
Beginning Balance at Dec. 31, 2017	36
Share-based Payments Subject to Redemption
Share-based compensation, net of issuance	(4)
Ending Balance at Sep. 30, 2018	32
Beginning Balance at Mar. 31, 2018	27
Share-based Payments Subject to Redemption
Share-based compensation, net of issuance	4
Ending Balance at Jun. 30, 2018	31
Share-based Payments Subject to Redemption
Share-based compensation, net of issuance	1
Ending Balance at Sep. 30, 2018	32
Beginning Balance at Dec. 31, 2018	37
Share-based Payments Subject to Redemption
Share-based compensation, net of issuance	(16)
Ending Balance at Mar. 31, 2019	21
Beginning Balance at Dec. 31, 2018	37
Share-based Payments Subject to Redemption
Share-based compensation, net of issuance	(9)
Ending Balance at Sep. 30, 2019	28
Beginning Balance at Mar. 31, 2019	21
Share-based Payments Subject to Redemption
Share-based compensation, net of issuance	4
Ending Balance at Jun. 30, 2019	25
Share-based Payments Subject to Redemption
Share-based compensation, net of issuance	3
Ending Balance at Sep. 30, 2019	$ 28