Supplemental Cash Flow Statement Disclosures (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Cash, Cash Equivalents and Restricted Cash
Cash and cash equivalents	$ 801	$ 1,798	$ 603	$ 721
Current restricted cash	$ 10	8	$ 6	7
Location of current restricted cash	us-gaap:OtherAssetsCurrent		us-gaap:OtherAssetsCurrent
Cash in assets held for sale			$ 63
Total cash, cash equivalents and restricted cash	$ 811	1,806	$ 672	$ 728
Other Non-cash items
PP&E acquired but not yet paid	$ 235	$ 224