Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financial Instruments
Cash and cash equivalents	$ 258	$ 285
7.25% 2063 Senior Notes
Financial Instruments
Interest rate	7.25%
7.25% 2064 Senior Notes
Financial Instruments
Interest rate	7.25%
6.95% Senior Notes
Financial Instruments
Interest rate	6.95%
6.7% Senior Notes
Financial Instruments
Interest rate	6.70%
Book Value
Financial Instruments
Cash and cash equivalents	$ 258	285
Book Value \| Retail
Financial Instruments
Long-term debt	917	917
Book Value \| Institutional
Financial Instruments
Long-term debt	535	534
Book Value \| Other
Financial Instruments
Long-term debt	83	83
Fair Value \| Level 1
Financial Instruments
Cash and cash equivalents	258	285
Fair Value \| Level 2 \| Retail
Financial Instruments
Long-term debt	795	943
Fair Value \| Level 2 \| Institutional
Financial Instruments
Long-term debt	527	594
Fair Value \| Level 2 \| Other
Financial Instruments
Long-term debt	$ 83	$ 83
Interest rate \| Institutional and Other \| Minimum
Financial Instruments
Fair value assumption, interest rate	2.74%	3.55%
Interest rate \| Institutional and Other \| Maximum
Financial Instruments
Fair value assumption, interest rate	7.05%	5.73%

No definition available.

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

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3044-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118951113&loc=d3e6676-107765

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebtNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Interest rate assumption used in valuing an instrument.

+ References

No definition available.

+ Details

Name:	usm_LongtermDebtMeasurementInput1
Namespace Prefix:	usm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant