Represents the number of categories in which the entity categorizes the products and services.

No definition available.

Name:	ctq_NumberOfCategoriesOfProductsAndServices
Namespace Prefix:	ctq_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the taxes and surcharges on revenues from universal service funds (USF), which are included in operating revenues and expenses.

+ References

No definition available.

+ Details

Name:	ctq_UniversalServiceFundsTaxesAndSurcharges
Namespace Prefix:	ctq_
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_EntityWideInformationRevenueFromExternalCustomerLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

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

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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

- Details

Name:	us-gaap_ProductOrServiceAxis=ctq_StrategicServicesQCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=ctq_LegacyServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=ctq_AffiliatesAndOtherServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Products and Services Revenues (Details) $ in Millions	3 Months Ended								12 Months Ended
Products and Services Revenues (Details) $ in Millions	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) category	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Products and Services Revenues
Number of categories of products and services (categories) \| category									3
Operating revenues	$ 2,114	$ 2,141	$ 2,133	$ 2,162	$ 2,208	$ 2,226	$ 2,223	$ 2,253	$ 8,550	$ 8,910	$ 8,964
Taxes and surcharges included in operating revenues and expenses									$ 134	149	147
Number of reportable segments									1
Strategic services
Products and Services Revenues
Operating revenues									$ 2,686	2,696	2,617
Legacy services
Products and Services Revenues
Operating revenues									2,831	3,216	3,593
Affiliates and other services
Products and Services Revenues
Operating revenues									$ 3,033	$ 2,998	$ 2,754