Employee Benefits - Health Care and Life Insurance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Health Care and Life Insurance [Abstract]
Health care benefit expenses	$ 132	$ 171	$ 211

Represents the health care benefit expenses for the active employees health care plan.

No definition available.

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