Loss Contingency, Asserted Claim

No definition available.

Name:	ctl_LossContingencyAssertedClaim
Namespace Prefix:	ctl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Site Contingency, Number Of Properties With Potential Environmental Liability

+ References

No definition available.

+ Details

Name:	ctl_SiteContingencyNumberOfPropertiesWithPotentialEnvironmentalLiability
Namespace Prefix:	ctl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementAmountAwardedToOtherParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of litigation expense, including but not limited to legal, forensic, accounting, and investigative fees.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14557-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14435-108349

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14326-108349

+ Details

Name:	us-gaap_LossContingencyDamagesSoughtValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14435-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14557-108349

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118943654&loc=d3e12021-110248

+ Details

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

- Definition

Number of plaintiffs that have filed claims pertaining to a loss contingency.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingencyNumberOfPlaintiffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of another entity's patents that the entity has allegedly infringed.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingencyPatentsAllegedlyInfringedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of pending claims pertaining to a loss contingency.

+ References

+ Details

Name:	us-gaap_LossContingencyPendingClaimsNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The difference between the maximum amount of estimated loss and the amount recorded as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 05
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=99385795&loc=d3e12631-108344

+ Details

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

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_UnfavorableRegulatoryActionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatutoryAccountingPracticesByJurisdictionAxis=ctl_U.S.DistrictCourtfortheDistrictofMinnesotaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationStatusAxis=us-gaap_PendingLitigationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ctl_LitigationByCaseAxis=ctl_PeruvianTaxLitigationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ctl_LitigationByCaseAxis=ctl_BrazilianTaxClaimsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=ctl_InterexchangeCarriersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=ctl_MissouriMunicipalitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationStatusAxis=us-gaap_JudicialRulingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ctl_Level3ParentLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments and Contingencies and Other Items (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Feb. 28, 2017 USD ($) lawsuit	Mar. 31, 2020 USD ($) property plaintiff lawsuit	Dec. 31, 2005 USD ($)
Loss Contingencies
Estimate of possible loss		$ 143,000
Patents allegedly infringed \| lawsuit	1
Number of properties with potential environmental liability \| property		200
Unfavorable Regulatory Action
Loss Contingencies
Estimate of possible loss		$ 100,000
U.S. District Court for the District of Minnesota
Loss Contingencies
Litigation settlement amount		15,500
Litigation settlement, expense		$ 3,500
Number of members (more than) \| plaintiff		22,000
Pending litigation \| Peruvian Tax Litigation
Loss Contingencies
Estimate of possible loss		$ 6,000
Loss contingency, asserted claim			$ 26,000
Pending litigation \| Brazilian Tax Claims
Loss Contingencies
Loss contingency, range of possible loss, portion not accrued		37,000
Pending litigation \| Brazilian Tax Claims \| Maximum
Loss Contingencies
Loss contingency, range of possible loss, portion not accrued		$ 42,000
Interexchange Carriers
Loss Contingencies
Number of lawsuits \| lawsuit		100
Missouri municipalities \| Judicial ruling
Loss Contingencies
Litigation settlement amount	$ 4,000
Level 3 Parent, LLC
Loss Contingencies
Damages sought, value		$ 50,000