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Investments in Unconsolidated Entities, Narrative (Details) $ in Millions | Mar. 31, 2018 USD ($)
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Equity Securities without Readily Determinable Fair Value [Line Items] |
Measurement alternative, impairment | $ 0
Measurement alternative, observable price change | $ 0

X
- Definition Amount of cumulative impairment loss on investment in equity security without readily determinable fair value. + References No definition available. + Details
Name: | usm_EquitySecuritiesWithoutReadilyDeterminableFairValueImpairmentLossCumulativeAmount
Namespace Prefix: | usm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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. + References No definition available. + Details
Name: | usm_EquitySecuritiesWithoutReadilyDeterminableFairValueLineItems
Namespace Prefix: | usm_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of cumulative gain from upward price adjustment on investment in equity security without readily determinable fair value. + References No definition available. + Details
Name: | usm_EquitySecuritiesWithoutReadilyDeterminableFairValueUpwardPriceAdjustmentCumulativeAmount
Namespace Prefix: | usm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant