Intangible Assets - Schedules (Details) - Licenses - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Indefinite-lived Intangible Assets [Line Items]
Balance at beginning of year	$ 2,223	$ 1,886
Acquisitions	8	331
Transferred to Assets held for sale	(51)	(10)
Divestitures	(11)	0
Exchanges - Licenses received	18	25
Exchanges - Licenses surrendered	(1)	(9)
Balance at end of year	$ 2,186	$ 2,223

The increase (decrease) during the period in book value of long-lived assets that the reporting entity plans to sell within one year (or one business cycle).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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- 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.

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- Definition

Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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- Definition

Amount of divestiture of an asset lacking physical substance and having a projected indefinite period of benefit to fair value. Excludes financial assets and goodwill.

+ References

No definition available.

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- Definition

Amount of increase in assets, excluding financial assets and goodwill, lacking physical substance with an indefinite life, from an acquisition.

+ References

No definition available.

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- Definition

Amount of assets received, excluding financial assets and goodwill, lacking physical substance with an indefinite life, from an exchange.

+ References

No definition available.

+ Details

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- Definition

Amount of assets disposed of, excluding financial assets and goodwill, lacking physical substance with an indefinite life, in an exchange.

+ References

No definition available.

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Namespace Prefix:	usm_
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