Long-Term Debt and Credit Facilities - Repurchases of Debt Instruments (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Nov. 30, 2024	Sep. 24, 2024
Long-term Debt and Credit Facilities
Net (loss) gain on early retirement of debt	$ 275	$ 348	$ 618	$ 214
Principal Amount Repurchased		376
Notes and Debt Instruments
Long-term Debt and Credit Facilities
Net (loss) gain on early retirement of debt		40
Term Loan | Term Loan A
Long-term Debt and Credit Facilities
Principal Amount Repurchased		2
Term Loan | Term Loan B-1
Long-term Debt and Credit Facilities
Principal Amount Repurchased		7
Term Loan | Term Loan B-2
Long-term Debt and Credit Facilities
Principal Amount Repurchased		$ 7
Senior Notes | 5.625% Senior Notes, Series X, due 2025
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		5.625%			5.625%
Principal Amount Repurchased		$ 70
Senior Notes | 7.200% Senior Notes, Series D, due 2025
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		7.20%			7.20%
Principal Amount Repurchased		$ 13
Senior Notes | 6.875% Debentures, Series G, due 2028
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		6.875%			6.875%	6.875%
Principal Amount Repurchased		$ 7
Senior Notes | 4.500% Senior Notes due 2029
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		4.50%				4.50%
Principal Amount Repurchased		$ 24
Senior Notes | 4.125% Superpriority Notes due 2029-2030
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		4.125%
Principal Amount Repurchased		$ 3
Senior Notes | 7.600% Senior Notes due 2039
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		7.60%
Principal Amount Repurchased		$ 5
Senior Notes | 7.650% Senior Notes due 2042
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		7.65%
Principal Amount Repurchased		$ 6
Senior Notes | 4.250% Senior Notes due 2028 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		4.25%			4.25%
Principal Amount Repurchased		$ 34
Senior Notes | 3.625% Senior Notes due 2029 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		3.625%
Principal Amount Repurchased		$ 81
Senior Notes | 3.750% Senior Notes due 2029 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		3.75%
Principal Amount Repurchased		$ 86
Senior Notes | 3.875% Senior Notes due 2029 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		3.875%
Principal Amount Repurchased		$ 18
Senior Notes | 7.250% Senior Notes due 2025 | Qwest Corporation
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		7.25%
Principal Amount Repurchased		$ 13