Long-Term Debt and Credit Facilities - Term Loans and Certain Other Debt of Subsidiaries (Details) - USD ($) $ in Millions			12 Months Ended
	Oct. 23, 2020	Nov. 27, 2019	Dec. 31, 2023	Dec. 31, 2022
Qwest Corporation | Term Loan
Long-term Debt and Credit Facilities
Long-term debt, gross			$ 215	$ 215
Qwest Corporation | Term Loan | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)			2.50%
Qwest Corporation | CoBank ACB | Variable Rate Term Loan
Long-term Debt and Credit Facilities
Proceeds from issuance of debt	$ 215
Qwest Corporation | CoBank ACB | Variable Rate Term Loan | Minimum | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)	1.50%
Qwest Corporation | CoBank ACB | Variable Rate Term Loan | Minimum | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)	0.50%
Qwest Corporation | CoBank ACB | Variable Rate Term Loan | Maximum | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.50%
Qwest Corporation | CoBank ACB | Variable Rate Term Loan | Maximum | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)	1.50%
Level 3 Financing, Inc. | Term Loan | Tranche B 2027 Term Loan
Long-term Debt and Credit Facilities
Long-term debt, gross			$ 2,411	$ 2,411
Level 3 Financing, Inc. | Term Loan | SOFR | Tranche B 2027 Term Loan
Long-term Debt and Credit Facilities
Basis spread (as a percent)		1.00%	1.75%
Level 3 Financing, Inc. | Term Loan | SOFR | Tranche B 2027 Term Loan - Eurodollar
Long-term Debt and Credit Facilities
Basis spread (as a percent)		1.75%
Level 3 Financing, Inc. | Term Loan | Base Rate | Tranche B 2027 Term Loan
Long-term Debt and Credit Facilities
Basis spread (as a percent)		0.75%
Level 3 Financing, Inc. | Term Loan | Federal Funds Effective Rate | Tranche B 2027 Term Loan
Long-term Debt and Credit Facilities
Basis spread (as a percent)		0.50%