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Revenues and Accounts Receivable - Counterparty Deficiencies (Details) - USD ($)
$ in Millions
Jun. 30, 2021
Dec. 31, 2020
Minimum Volume Commitments [Line Items]    
Counterparty deficiencies billed and collected $ 139 $ 501
Minimum Volume Commitments    
Minimum Volume Commitments [Line Items]    
Counterparty deficiencies billed and collected 54 73
Counterparty deficiencies unbilled 21 4
Counterparty deficiencies $ 75 $ 77