CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Statement of Cash Flows [Abstract]
Cash and cash equivalents	$ 237	$ 105	$ 174
Restricted cash included in Prepaid expenses and other current assets	12		10
Total cash, cash equivalents, and restricted cash at end of the period	$ 249	$ 114	$ 184	$ 197