Supplemental Cash Flow Statement Disclosures (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Cash, Cash Equivalents and Restricted Cash
Cash and cash equivalents	$ 1,446	$ 1,366	$ 771	$ 1,798
Current restricted cash	$ 12	15	$ 12	8
Location of current restricted cash	Other current assets		Other current assets
Total cash, cash equivalents and restricted cash	$ 1,458	1,381	$ 783	$ 1,806
Other Non-cash items
PP&E acquired but not yet paid	$ 550	$ 409

Future cash outflow to pay for purchases of fixed assets that have occurred.

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