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Organization and Basis of Presentation - Activity in Uncollectable Accounts (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Beginning balance $ 46 $ 50
Charged to income 19 81
Charged to other accounts 14 47
Write-offs (35) (132)
Ending balance $ 44 $ 46