CenturyLink Merger - Acquisition Related Costs (Details) - Level 3 Parent, LLC - USD ($)	2 Months Ended	10 Months Ended	12 Months Ended
Dec. 31, 2017	Oct. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Transaction-related expenses	$ 0	$ 18,000,000	$ 0	$ 1,000,000
Integration and transformation-related expenses	28,000,000	67,000,000	82,000,000	120,000,000
Total acquisition-related expenses	$ 28,000,000	$ 85,000,000	$ 82,000,000	$ 121,000,000

Amount of direct costs of the business combination including legal, accounting, other costs incurred to consummate the business acquisition, and amount of costs incurred to effect a business combination, including business integration costs, systems integration and conversion costs, and severance and other employee-related costs.

No definition available.

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