Long-Term Debt and Credit Facilities - Long Term Debt (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2025 USD ($) subsidiary	Dec. 31, 2024 USD ($)
Debt Disclosure [Abstract]
Number of subsidiaries | subsidiary	3
Long-term Debt and Credit Facilities
Finance lease and other obligations	$ 241,000,000	$ 254,000,000
Unamortized discounts, net	(408,000,000)	(395,000,000)
Unamortized debt issuance costs	(216,000,000)	(217,000,000)
Total long-term debt	17,896,000,000	17,906,000,000
Less current maturities	(331,000,000)	(412,000,000)
Long-term debt, excluding current maturities	$ 17,565,000,000	17,494,000,000
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 | Term Loan A
Long-term Debt and Credit Facilities
Basis spread (as a percent)	6.00%
Long-term debt, gross	$ 347,000,000	$ 357,000,000
Long-term debt, weighted average interest rate	10.327%	10.573%
Term Loan | Term Loan B-1
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.35%
Long-term debt, gross	$ 1,598,000,000	$ 1,606,000,000
Long-term debt, weighted average interest rate	6.791%	7.037%
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	$ 0	$ 1,199,000,000
Long-term debt, weighted average interest rate		11.133%
Term Loan | Term Loan B-2
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.35%
Long-term debt, gross	$ 1,598,000,000	$ 1,606,000,000
Long-term debt, weighted average interest rate	6.791%	7.037%
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	$ 0	$ 1,199,000,000
Long-term debt, weighted average interest rate		11.133%
Term Loan | Term Loan B
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.25%
Long-term debt, gross	$ 56,000,000	$ 56,000,000
Long-term debt, weighted average interest rate	6.691%	6.937%
Term Loan | Term Loan B-3 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Basis spread (as a percent)	4.25%
Long-term debt, gross	$ 2,400,000,000	$ 0
Long-term debt, weighted average interest rate	8.577%
Term Loan | 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	$ 12,000,000
Long-term debt, weighted average interest rate	6.191%	6.437%
Senior Notes | Superpriority Notes Due on Various Dates
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 1,247,000,000	$ 1,247,000,000
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 | First Lien Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate	6.875%
Long-term debt, gross	$ 4,087,000,000	3,846,000,000
Senior Notes | First Lien Notes | Level 3 Financing, Inc. | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	6.875%
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	2,579,000,000
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 | Senior Notes Maturing 2028-2042
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 1,296,000,000	1,428,000,000
Senior Notes | Senior Notes Maturing 2028-2042 | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	4.50%
Senior Notes | Senior Notes Maturing 2028-2042 | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	7.65%
Senior Notes | Senior Notes Maturing 2028-2029 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 894,000,000	964,000,000
Senior Notes | Senior Notes Maturing 2028-2029 | Level 3 Financing, Inc. | Minimum
Long-term Debt and Credit Facilities
Stated interest rate	3.625%
Senior Notes | Senior Notes Maturing 2028-2029 | Level 3 Financing, Inc. | Maximum
Long-term Debt and Credit Facilities
Stated interest rate	4.25%
Senior Notes | Senior Notes Maturing 2025-2057 | Qwest Corporation
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 1,973,000,000	1,973,000,000
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%