Employee Benefits - Additional Information (Details) shares in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2022 USD ($)	Dec. 31, 2023	Dec. 31, 2022 USD ($) retiree shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Jan. 01, 2022 USD ($) Employee	Dec. 31, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Benefits paid, net of participant contributions and direct subsidy receipts			$ 210,000,000
Expected future benefit payment, next twelve months, net of direct subsidies			$ 210,000,000
Ultimate health care cost trend rate			4.50%
Commingled funds, redemption notice period			180 days
Actual (losses) gains			$ (987,000,000)	$ 422,000,000
Expected return on plan assets			329,000,000	$ 535,000,000
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]				Other income (expense), net
Difference between the actual and expected returns on pension and post-retirement plan assets			(1,300,000,000)	$ (113,000,000)
Active health care benefit expenses			296,000,000	309,000,000	$ 307,000,000
Participating employees' contribution to health care plan			$ 101,000,000	$ 120,000,000	133,000,000
Common stock included in the assets of the Defined Contribution Plan (in shares) | shares			10	10
Expenses related to the 401(k) Plan			$ 91,000,000	$ 96,000,000	101,000,000
US
Defined Benefit Plan Disclosure [Line Items]
Pension liability				1,400,000,000
Change in Assumptions for Defined Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation				37,000,000	(3,000,000)
Minimum
Defined Benefit Plan Disclosure [Line Items]
Expected health care cost trend rate			5.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Expected health care cost trend rate			7.20%
Combined Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan			$ (580,000,000)	(1,147,000,000)
Expected future benefits, next twelve months			566,000,000
One-time special termination charge				6,000,000	21,000,000
Settlements				383,000,000
Benefit obligation			$ 5,295,000,000	9,678,000,000	12,202,000,000		$ 12,217,000,000
Short term interest crediting rates			3.75%
Long term interest crediting rates			3.50%
Fair value of plan assets			$ 4,715,000,000	$ 8,531,000,000	$ 10,546,000,000		10,493,000,000
Expected long-term rate of return on plan assets			5.50%	5.50%	6.50%
Expected long-term rate of return on plan assets before administrative expenses			6.50%
Actual (losses) gains			$ (987,000,000)	$ 422,000,000	$ 1,210,000,000
Combined Pension Plan | Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets		7.00%
Combined Pension Plan | New Lumen Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions	$ 319,000,000
Benefit obligation						$ 2,500,000,000
Fair value of plan assets						$ 2,200,000,000
Number of active participants (in employees) | Employee						2,500
Number of other participants (in employees) | Employee						19,000
Combined Pension Plan | Debt Security
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percentage			55.00%
Combined Pension Plan | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percentage			45.00%
Combined Pension Plan | US
Defined Benefit Plan Disclosure [Line Items]
Number of retirees | retiree			22,600
Combined Pension Plan | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan			$ (580,000,000)	(1,100,000,000)
Contributions			0	0
Settlements			0	383,000,000	0
Expected return on plan assets			385,000,000	535,000,000	593,000,000
Combined Pension Plan | Nonqualified Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan			(35,000,000)	(46,000,000)
Benefits paid by company			5,000,000	5,000,000
Expected future benefits, next twelve months			$ 5,000,000
Combined Pension Plan | Level 3 Parent, LLC
Defined Benefit Plan Disclosure [Line Items]
Amortization period of the plan shortfall			7 years
Combined Pension Plan | Legacy Level 3
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan				(17,000,000)
Post-Retirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan			$ (1,990,000,000)	(2,776,000,000)
Contributions			0	0
Benefits paid by company			249,000,000	$ 247,000,000	$ 255,000,000
Expected future benefits, next twelve months			$ 213,000,000
Ultimate health care cost trend rate			4.50%	4.50%	4.50%
Benefit obligation			$ 1,995,000,000	$ 2,781,000,000	$ 3,048,000,000		$ 3,037,000,000
Fair value of plan assets			$ 5,000,000	$ 5,000,000	$ 5,000,000
Expected long-term rate of return on plan assets			4.00%	4.00%	4.00%
Expected return on plan assets			$ 0	$ 0	$ 1,000,000
Post-Retirement Benefit Plans | Minimum
Defined Benefit Plan Disclosure [Line Items]
Expected health care cost trend rate			5.00%	5.00%
Post-Retirement Benefit Plans | Maximum
Defined Benefit Plan Disclosure [Line Items]
Expected health care cost trend rate			7.20%	5.75%