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

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.

Name:	us-gaap_DisaggregationOfRevenueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration