Summary of Significant Accounting Policies - Schedule Of Allowance For Uncollectible Accounts (Details) - USD ($) $ in Millions |
12 Months Ended | ||
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Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Allowance for Doubtful Accounts Receivable [Roll Forward] | |||
| Allowances, beginning of year | $ 29 | $ 10 | $ 5 |
| Amounts charged to expense | 35 | 33 | 12 |
| Write-offs of uncollectible receivables | (40) | (14) | (7) |
| Allowances, end of year | $ 24 | $ 29 | $ 10 |
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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 The carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross premiums receivable to net realizable value. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount of increase in the allowance for premiums receivable from charges to expense. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The amount of decrease during the period to the valuation allowance account representing portions of such account associated with premium receivables that have been determined to be absolutely uncollectible or that were sold or transferred, and which receivables were simultaneously written off. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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