Equipment Installment Plan Receivables, Gross Receivables by Credit Category (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Equipment installment plan receivables, gross	$ 887	$ 873
Unbilled
Financing Receivable, Recorded Investment [Line Items]
Equipment installment plan receivables	846	827
Billed
Financing Receivable, Recorded Investment [Line Items]
Equipment installment plan receivables	27	32
Equipment installment plan receivables, past due	14	14
Lower Risk
Financing Receivable, Recorded Investment [Line Items]
Equipment installment plan receivables, gross	866	850
Lower Risk \| Unbilled
Financing Receivable, Recorded Investment [Line Items]
Equipment installment plan receivables	828	807
Lower Risk \| Billed
Financing Receivable, Recorded Investment [Line Items]
Equipment installment plan receivables	26	31
Equipment installment plan receivables, past due	12	12
Higher Risk
Financing Receivable, Recorded Investment [Line Items]
Equipment installment plan receivables, gross	21	23
Higher Risk \| Unbilled
Financing Receivable, Recorded Investment [Line Items]
Equipment installment plan receivables	18	20
Higher Risk \| Billed
Financing Receivable, Recorded Investment [Line Items]
Equipment installment plan receivables	1	1
Equipment installment plan receivables, past due	$ 2	$ 2

Financing receivables that are current.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

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Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(3))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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