Revenues and Accounts Receivable - Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Change in Contract Liabilities [Roll Forward]
Beginning balance	$ 501	$ 354	$ 501	$ 354
Amounts recognized as revenue			(393)	(246)
Additions			33	393
Ending balance			141	501
Crude Oil Sales Agreements Entered Into In Conjunction WIth Storage Arrangements And Future Inventory Exchanges
Change in Contract Liabilities [Roll Forward]
Beginning balance	361		361
Additions	$ 361	$ 155
Ending balance			$ 0	$ 361