Loss Contingency, Asserted Claim

No definition available.

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

- Definition

The number of pending cases for which the court entered a final order.

+ References

No definition available.

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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=82911808&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=82911808&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=82911808&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=82911808&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=82911808&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=115931803&loc=d3e12021-110248

+ Details

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

- Definition

The total number of new claims filed pertaining to a loss contingency during the period.

+ References

+ Details

Name:	us-gaap_LossContingencyNewClaimsFiledNumber
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

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

- Details

Name:	us-gaap_StatutoryAccountingPracticesByJurisdictionAxis=ctl_LouisianaStateCourtMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_StatutoryAccountingPracticesByJurisdictionAxis=ctl_LouisianaFederalCourtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ctl_Level3ParentLLCMember
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_PeruvianTaxLitigationBeforeInterestMember
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_EmployeeSeveranceandContractorTerminationDisputesMember
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:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	dei_LegalEntityAxis=ctl_CenturyLinkInc.Member
Namespace Prefix:
Data Type:	na
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- Details

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- Details

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Commitments and Contingencies and Other Items (Details) $ in Millions	1 Months Ended	6 Months Ended	9 Months Ended
	Feb. 28, 2017 USD ($) lawsuit	Sep. 30, 2018 USD ($) lawsuit	Sep. 30, 2018 USD ($) lawsuit	Dec. 31, 2017 USD ($)	Dec. 31, 2005 USD ($)
Loss Contingencies
Estimate of possible loss		$ 138	$ 138
New claims filed, number \| lawsuit		6
Letters of credit outstanding, amount		$ 129	$ 129	$ 104
Patents allegedly infringed \| lawsuit			1
Louisiana State Court
Loss Contingencies
New claims filed, number \| lawsuit		2
Louisiana Federal Court
Loss Contingencies
New claims filed, number \| lawsuit		4
Level 3 Parent, LLC
Loss Contingencies
Loss contingency, damages sought, value			$ 50
Level 3 Parent, LLC \| Pending litigation \| Peruvian Tax Litigation, Before Interest
Loss Contingencies
Loss contingency, asserted claim					$ 26
Level 3 Parent, LLC \| Pending litigation \| Peruvian Tax Litigation
Loss Contingencies
Loss contingency, asserted claim		$ 13	13
Level 3 Parent, LLC \| Pending litigation \| Employee Severance and Contractor Termination Disputes
Loss Contingencies
Loss contingency, asserted claim		30	30
Level 3 Parent, LLC \| Pending litigation \| Brazilian Tax Claims \| Maximum
Loss Contingencies
Loss contingency, range of possible loss, portion not accrued		$ 34	$ 34
Interexchange Carriers \| CenturyLink, Inc.
Loss Contingencies
Number of lawsuits \| lawsuit		100	100
Missouri municipalities \| Judicial ruling
Loss Contingencies
Number of cases, final court order \| lawsuit	1
Litigation settlement amount	$ 4