Revenue (Nature of Services and Products) (Details)  | 
3 Months Ended | 
|---|---|
| 
 Mar. 31, 2018  
payment 
 | |
| Certain wireless devices | |
| Disaggregation of Revenue [Line Items] | |
| Program period | 24 months | 
| Trade-in equipment | |
| Disaggregation of Revenue [Line Items] | |
| Number of installment plan payments | 12 | 
| X | ||||||||||
- Definition Equipment Installment Plan Payment Term No definition available. 
  | 
| X | ||||||||||
- Definition Number of Installment Plan Payments required for right to trade-in handset. No definition available. 
  | 
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
  | 
| X | ||||||||||
- Details 
  | 
| X | ||||||||||
- Details 
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