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Revenues and Accounts Receivable - Contract Balances (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Change in Contract Liabilities [Roll Forward]    
Beginning balance $ 354 $ 338
Amounts recognized as revenue (246) (227)
Additions 393 244
Other   (1)
Ending balance 501 354
Crude Oil Sales Agreements Entered Into In Conjunction WIth Storage Arrangements And Future Inventory Exchanges    
Change in Contract Liabilities [Roll Forward]    
Beginning balance 155  
Additions 361 155
Ending balance $ 361 $ 155