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Long-Term Debt and Credit Facilities - Impact of Recent Debt Transactions, Additional Information (Details) $ in Millions		3 Months Ended			9 Months Ended
	Sep. 24, 2024 USD ($) series	Sep. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)
Long-term Debt and Credit Facilities
Face amount		$ 11,938			$ 11,938
Repayments of debt					2,258
Reduction of debt	$ 60
Debt fees		14			14
Amount of debt extinguished					744
Net gain on early retirement of debt		(1)	$ 275	$ 0	277	$ 618
Reduction in debt from fair value adjustment					492
Payment for lender fees					209
Payment for third-party costs					174
Debt instrument, capitalized lender fees		52			52
Third party costs capitalized		62			62
Gain (Loss) on Extinguishment of Debt
Long-term Debt and Credit Facilities
Debt instrument, lender fees					157
Selling, General and Administrative Expense
Long-term Debt and Credit Facilities
Debt instrument, third-party costs					112
Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Amount of debt extinguished					2,600
Senior Notes
Long-term Debt and Credit Facilities
Face amount		848			848
Net gain on early retirement of debt					3
Senior Notes \| 10.000% Secured Notes Due 2032
Long-term Debt and Credit Facilities
Face amount	$ 438
Stated interest rate	10.00%
Senior Notes \| Senior Unsecured Notes Due 2026-2032
Long-term Debt and Credit Facilities
Face amount	$ 491
Repayments of debt	$ 14
Number of series \| series	4
Senior Notes \| 10.000% Second Lien Notes Due 2032 \| Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Face amount	$ 350
Stated interest rate	10.00%
Senior Notes \| Senior Unsecured Notes Due 2027 \| Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Face amount	$ 357
Number of series \| series	2
Senior Notes \| Lumen and Qwest, Senior Unsecured Notes Due 2025
Long-term Debt and Credit Facilities
Repurchased face amount		19			19
Senior Notes \| Senior Unsecured Notes Due 2025
Long-term Debt and Credit Facilities
Repurchased face amount							$ 75
Superpriority Notes and Term Loans
Long-term Debt and Credit Facilities
Repurchased face amount		$ 19			$ 19