Long-Term Debt and Credit Facilities - Cash Tender Offers (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Sep. 24, 2024	Nov. 30, 2024	Dec. 31, 2024
Long-term Debt and Credit Facilities
Reduction of debt	$ 60	$ 393
Gain (loss) on cash tender offers			$ 33
Debt instrument, face amount			$ 11,925
Senior Notes
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 848	$ 393
5.625% Senior Notes, Series X, due 2025 | Senior Notes
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		5.625%	5.625%
Debt instrument, face amount		$ 33
7.200% Senior Notes, Series D, due 2025 | Senior Notes
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		7.20%	7.20%
Debt instrument, face amount		$ 3
5.125% Senior Notes due 2026 | Senior Notes
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	5.125%	5.125%
Debt instrument, face amount	$ 137	$ 5
4.000% Senior Secured Notes due 2027 (unsecured) | Senior Notes
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	4.00%	4.00%
Debt instrument, face amount	$ 188	$ 4
6.875% Debentures, Series G, due 2028 | Senior Notes
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	6.875%	6.875%	6.875%
Debt instrument, face amount	$ 80	$ 24
3.400% Senior Secured Notes due 2027 (unsecured) | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	3.40%	3.40%
Debt instrument, face amount	$ 77	$ 1
4.625% Senior Notes due 2027 | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	4.625%	4.625%
Debt instrument, face amount	$ 280	$ 48
4.250% Senior Notes due 2028 | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		4.25%	4.25%
Debt instrument, face amount		$ 275