Revenue Recognition - Contract Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Jan. 01, 2018
Contract Liabilities
Balance at December 31, 2017	$ 0
Change in accounting policy - Deferred revenues reclassification		$ 167
Change in accounting policy - Retained earnings impact		$ (21)
Contract additions	154
Terminated contracts	(2)
Revenue recognized	(135)
Balance at December 31, 2018	$ 163

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130531-203044

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130532-203044

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	duration

- Definition

Amount of increase (decrease) in revenue recognized from contract additions which increases (decreases) right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

No definition available.

+ Details

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Namespace Prefix:	usm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Amount of increase (decrease) in revenue recognized from contract terminations which increases (decreases) right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment in initial period of adoption for revenue from contract with customer.

+ References

No definition available.

+ Details

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Namespace Prefix:	usm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Effect in current period from application of guidance for revenue from contract with customer on contract liabilities on upon adoption.

+ References

No definition available.

+ Details

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Namespace Prefix:	usm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant