CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Statement of Cash Flows [Abstract]
Cash and cash equivalents	$ 1,025	$ 1,370	$ 1,509
Restricted cash included in Prepaid expenses, assets held-for-sale and other current assets	17		11
Total cash, cash equivalents, and restricted cash at end of the period	$ 1,042	$ 1,386	$ 1,520	$ 232