CenturyLink Merger - Acquisition Related Costs (Details) - Level 3 Parent, LLC - USD ($) $ in Millions	2 Months Ended	10 Months Ended	12 Months Ended
Dec. 31, 2017	Oct. 31, 2017	Dec. 31, 2018	Dec. 31, 2016
Business Acquisition [Line Items]
Transaction-related expenses	$ 0		$ 1
Integration-related expenses	28		120
Total acquisition-related expenses	$ 28		$ 121
Predecessor
Business Acquisition [Line Items]
Transaction-related expenses		$ 18		$ 0
Integration-related expenses		67		15
Total acquisition-related expenses		$ 85		$ 15

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:	lvlt_BusinessCombinationTransactionCostsandIntegrationRelatedCosts
Namespace Prefix:	lvlt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration