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Variable Interest Entities - Narrative (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Variable Interest Entity [Line Items]      
Investment in unconsolidated entities, maximum exposure $ 5   $ 5
Capital contributions, loans or advances 50 $ 88  
USCC EIP LLC      
Variable Interest Entity [Line Items]      
Capital contributions, loans or advances $ 21 $ 67