Long-Term Debt and Credit Facilities - Long Term Debt (Details)	9 Months Ended
	Sep. 30, 2024 USD ($) subsidiary	Dec. 31, 2023 USD ($)
Debt Disclosure [Abstract]
Number of subsidiaries | subsidiary	3
Long-term Debt and Credit Facilities
Finance lease and other obligations	$ 263,000,000	$ 285,000,000
Unamortized discounts, net	(412,000,000)	(4,000,000)
Unamortized debt issuance costs	(228,000,000)	(145,000,000)
Total long-term debt	18,557,000,000	19,988,000,000
Less current maturities	(415,000,000)	(157,000,000)
Long-term debt, excluding current maturities	$ 18,142,000,000	19,831,000,000
Tranche B 2027 Term Loan | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Basis spread (as a percent)	1.75%
Long-term debt, gross	$ 12,000,000	2,411,000,000
Line of Credit | Series A Revolving Credit Facility
Long-term Debt and Credit Facilities
Basis spread (as a percent)	4.00%
Long-term debt, gross	$ 0	0
Line of Credit | Series B Revolving Credit Facility
Long-term Debt and Credit Facilities
Basis spread (as a percent)	6.00%
Long-term debt, gross	$ 0	0
Term Loan | Qwest Corporation
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.50%
Long-term debt, gross	$ 0	$ 215,000,000
Long-term debt, weighted average interest rate		7.97%
Term Loan | Term Loan A
Long-term Debt and Credit Facilities
Basis spread (as a percent)	6.00%
Long-term debt, gross	$ 362,000,000	$ 0
Long-term debt, weighted average interest rate	11.247%	7.464%
Term Loan | Term Loan B-1
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.35%
Long-term debt, gross	$ 1,610,000,000	$ 0
Long-term debt, weighted average interest rate	7.742%
Term Loan | Term Loan B-1 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Basis spread (as a percent)	6.56%
Long-term debt, gross	$ 1,199,000,000	0
Long-term debt, weighted average interest rate	11.838%
Term Loan | Term Loan B-2
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.35%
Long-term debt, gross	$ 1,610,000,000	0
Long-term debt, weighted average interest rate	7.742%
Term Loan | Term Loan B-2 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Basis spread (as a percent)	6.56%
Long-term debt, gross	$ 1,199,000,000	0
Long-term debt, weighted average interest rate	11.838%
Term Loan | Term Loan B
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.25%
Long-term debt, gross	$ 57,000,000	$ 3,891,000,000
Long-term debt, weighted average interest rate	7.611%	7.72%
Term Loan | Tranche B 2027 Term Loan | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Long-term debt, weighted average interest rate	7.111%	7.22%
Term Loan | Term Loan A-1
Long-term Debt and Credit Facilities
Long-term debt, weighted average interest rate		7.47%
Line of Credit and Term Loan | Other Facilities
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.00%
Long-term debt, gross	$ 0	$ 1,399,000,000
Senior Notes | Superpriority Notes Due on Various Dates
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 1,247,000,000	0
Senior Notes | Superpriority Notes Due on Various Dates | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	4.125%
Senior Notes | Superpriority Notes Due on Various Dates | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	10.00%
Senior Notes | 4.000% Senior Secured Notes Due 2027
Long-term Debt and Credit Facilities
Stated interest rate	4.00%
Long-term debt, gross	$ 0	1,250,000,000
Senior Notes | First Lien Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 3,846,000,000	925,000,000
Senior Notes | First Lien Notes | Level 3 Financing, Inc. | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	10.50%
Senior Notes | First Lien Notes | Level 3 Financing, Inc. | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	11.00%
Senior Notes | Second Lien Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 2,579,000,000	0
Senior Notes | Second Lien Notes | Level 3 Financing, Inc. | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	3.875%
Senior Notes | Second Lien Notes | Level 3 Financing, Inc. | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	10.00%
Senior Notes | Former Level 3 Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 0	1,500,000,000
Senior Notes | Former Level 3 Senior Notes | Level 3 Financing, Inc. | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	3.40%
Senior Notes | Former Level 3 Senior Notes | Level 3 Financing, Inc. | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	3.875%
Senior Notes | Senior Notes Maturing 2025-2042
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 1,539,000,000	2,143,000,000
Senior Notes | Senior Notes Maturing 2025-2042 | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	4.00%
Senior Notes | Senior Notes Maturing 2025-2042 | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	7.65%
Senior Notes | Senior Notes Maturing 2027-2029 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 1,508,000,000	3,940,000,000
Senior Notes | Senior Notes Maturing 2027-2029 | Level 3 Financing, Inc. | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	3.40%
Senior Notes | Senior Notes Maturing 2027-2029 | Level 3 Financing, Inc. | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	4.625%
Senior Notes | Senior Notes Maturing 2025-2057 | Qwest Corporation
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 1,974,000,000	1,986,000,000
Senior Notes | Senior Notes Maturing 2025-2057 | Qwest Corporation | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	6.50%
Senior Notes | Senior Notes Maturing 2025-2057 | Qwest Corporation | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	7.75%
Senior Notes | Senior Notes Maturing 2028-2031 | Qwest Capital Funding, Inc.
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 192,000,000	$ 192,000,000
Senior Notes | Senior Notes Maturing 2028-2031 | Qwest Capital Funding, Inc. | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	6.875%
Senior Notes | Senior Notes Maturing 2028-2031 | Qwest Capital Funding, Inc. | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	7.75%
Senior Notes | 10.500% Senior Secured Notes due 2030 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate	10.50%