Summary of Significant Accounting Policies (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
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| Accounts Receivable, Allowance for Credit Loss [Roll Forward] | |||
| Accounts Receivable, Allowance for Credit Loss, Beginning Balance | $ 47 | $ 52 | $ 61 |
| Provision for doubtful accounts | 37 | 16 | 8 |
| Accounts Receivable, Allowance for Credit Loss, Writeoff | (24) | (21) | (17) |
| Accounts Receivable, Allowance for Credit Loss, Ending Balance | $ 72 | $ 47 | $ 52 |
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- Definition Amount of allowance for credit loss on accounts receivable. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available.
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- Definition Amount of direct write-downs of accounts receivable charged against the allowance. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of expense (reversal of expense) for expected credit loss on accounts receivable. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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