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Employee Benefits - Pension Benefits, Additional Information (Details) - Combined Pension Plan - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2022 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Funded (unfunded) status of plan |  | $ (615,000,000) | $ (736,000,000) |
Contributions |  | 170,000,000 | 0 | $ 0
Expected future benefits, next twelve months |  | 569,000,000 |  |
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 |  | (615,000,000) | (736,000,000) |
Contributions |  | 170,000,000 | 0 |
Nonqualified Plan |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Funded (unfunded) status of plan |  | (30,000,000) | (33,000,000) |
Benefits paid by company |  | 4,000,000 | $ 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 |  |

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