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Summary of Significant Accounting Policies - Schedule Of Allowance For Uncollectible Accounts (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Allowances, beginning of year $ 24 $ 29 $ 10
Amounts charged to expense 134 35 33
Write-offs of uncollectible receivables (35) (40) (14)
Allowances, end of year $ 123 $ 24 $ 29