Long-Term Debt and Credit Facilities - Exchange Offers (Details) - USD ($)		3 Months Ended	12 Months Ended
	Apr. 17, 2023	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Nov. 30, 2024	Sep. 24, 2024	Mar. 31, 2023
Long-term Debt and Credit Facilities
Debt instrument, face amount			$ 11,925,000,000
Aggregate principal amount	$ 630,000,000
Repurchased face amount			376,000,000
Net (loss) gain on early retirement of debt		$ 275,000,000	$ 348,000,000	$ 618,000,000	$ 214,000,000
Senior Notes
Long-term Debt and Credit Facilities
Debt instrument, face amount						$ 393,000,000	$ 848,000,000
Level 3 Financing, Inc. | Senior Notes | 10.500% Senior Secured Notes due 2030
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 9,000,000	$ 915,000,000
Stated interest rate (as a percent)	10.50%	10.50%	10.50%
Lumen Technologies Incorporated | Senior Notes
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 19,000,000	$ 1,535,000,000
Repurchased face amount								$ 24,000,000