Threshold period for determining trade accounts receivable as past due in 'PnYnMnDTnHnMnS' format

No definition available.

Name:	ctl_AccountsReceivablePastDueThresholdDaysOutstanding
Namespace Prefix:	ctl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Cumulative Effect of New Accounting Principle in Period of Adoption, Tax

+ References

No definition available.

+ Details

Name:	ctl_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoptionTax
Namespace Prefix:	ctl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

Name:	ctl_NatureOfBusinessLineItems
Namespace Prefix:	ctl_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue from Contract with Customer, Contract Term

+ References

No definition available.

+ Details

Name:	ctl_RevenueFromContractWithCustomerContractTerm
Namespace Prefix:	ctl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue from Contract with Customer, Length of Customer Life

+ References

No definition available.

+ Details

Name:	ctl_RevenueFromContractWithCustomerLengthOfCustomerLife
Namespace Prefix:	ctl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the customer relationship period considered for recognition of revenue.

+ References

No definition available.

+ Details

Name:	ctl_RevenueRecognitionCustomerRelationshipPeriod
Namespace Prefix:	ctl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect

+ References

No definition available.

+ Details

Name:	ctl_TaxCutsandJobsActReclassificationfromAOCItoRetainedEarningsTaxEffect
Namespace Prefix:	ctl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Universal Service Fund Contributions

+ References

No definition available.

+ Details

Name:	ctl_UniversalServiceFundContributions
Namespace Prefix:	ctl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

+ References

No definition available.

+ Details

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

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13854-109267

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13777-109266

+ Details

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

- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

No definition available.

+ Details

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

- Definition

Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.

+ References

No definition available.

+ Details

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

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201602Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_RetainedEarningsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201409Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CustomerRelationshipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_ComputerSoftwareIntangibleAssetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_OtherIntangibleAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
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_MajorCustomersAxis=ctl_ConsumerCustomersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Background and Summary of Significant Accounting Policies (Details) $ in Millions		2 Months Ended	3 Months Ended		10 Months Ended	12 Months Ended
	Oct. 31, 2017 reporting_unit	Dec. 31, 2017 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) reporting_unit segment	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)
Description of Business
USF contributions		$ 71			$ 331	$ 428	$ 415
Past due threshold, days outstanding						30 days
Finite-lived intangible assets, useful life						9 years
Goodwill impairment		$ 0	$ 3,708		$ 0	$ 3,708	$ 0
Number of reporting units \| reporting_unit	1					1
Number of operating segments \| segment						1
Reclassification from AOCI to retained earnings, tax effect				$ 6
Operating lease assets						$ 1,060
Operating lease liabilities						1,103
Accounting Standards Update 2016-02
Description of Business
Operating lease assets								$ 1,300
Operating lease liabilities								$ 1,400
Accumulated deficit \| Accounting Standards Update 2014-09
Description of Business
Cumulative effect of adoption of ASU						9
Cumulative net effect of adoption of ASU, tax						3
Accumulated deficit \| Accounting Standards Update 2016-02
Description of Business
Cumulative effect of adoption of ASU						$ (39)
Customer relationships
Description of Business
Finite-lived intangible assets, useful life						10 years
Capitalized software
Description of Business
Finite-lived intangible assets, useful life						7 years
Other
Description of Business
Finite-lived intangible assets, useful life						5 years
Minimum
Description of Business
Contract term						1 year
Period company may receive up front payments for services to be provided in the future (in years)						10 years
Minimum \| Customer relationships
Description of Business
Finite-lived intangible assets, useful life						7 years
Maximum
Description of Business
Contract term						5 years
Period company may receive up front payments for services to be provided in the future (in years)						20 years
Maximum \| Customer relationships
Description of Business
Finite-lived intangible assets, useful life						14 years
Consumer Customers \| Minimum
Description of Business
Length of customer life						12 months
Consumer Customers \| Maximum
Description of Business
Length of customer life						60 months
Consumer Customers \| Weighted Average
Description of Business
Length of customer life						30 months