Employee Benefits - Pension Benefits, Additional Information (Details) - Combined Pension Plan - USD ($)	1 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Funded (unfunded) status of plan		$ (736,000,000)	$ (580,000,000)
Expected future benefits, next twelve months		574,000,000
New Lumen Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions	$ 319,000,000
Qualified Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Funded (unfunded) status of plan		(736,000,000)	(580,000,000)
Contributions		0	0
Nonqualified Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Funded (unfunded) status of plan		(33,000,000)	(35,000,000)
Benefits paid by company		5,000,000	$ 5,000,000
Expected future benefits, next twelve months		$ 4,000,000
Level 3 Parent, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization period of the plan shortfall (in years)		7 years