Accounts Receivable Accounts Receivable (Activity in the Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Allowance for Doubtful Accounts Receivable [Roll Forward] | |||
| Balance beginning of year | $ 97 | $ 86 | $ 91 |
| Additions- charged to expense | 72 | 107 | 82 |
| Deductions- write-offs | (78) | (96) | (87) |
| Balance end of year | $ 91 | $ 97 | $ 86 |
| X | ||||||||||
- Definition For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- 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.
|
| X | ||||||||||
- Definition Amount of direct write-downs of accounts receivable charged against the allowance. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Amount of expense related to write-down of receivables to the amount expected to be collected. Includes, but is not limited to, accounts receivable and notes receivable. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|