Long-Term Debt and Credit Facilities - Transaction Support Agreement Transactions - Debt (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Long-term Debt and Credit Facilities
Repaid	$ 2,258
Exchanged	10,244
Term Loan | Term Loan A
Long-term Debt and Credit Facilities
Repaid	933
Exchanged	0
Term Loan | Term Loan A-1
Long-term Debt and Credit Facilities
Repaid	266
Exchanged	0
Term Loan | Term Loan B
Long-term Debt and Credit Facilities
Repaid	575
Exchanged	3,259
Term Loan | Level 3 Financing, Inc. | Term Loan B
Long-term Debt and Credit Facilities
Repaid	0
Exchanged	2,398
Term Loan | Qwest Corporation | Term Loan B
Long-term Debt and Credit Facilities
Repaid	215
Exchanged	$ 0
Senior Notes | 5.125% Senior Notes due 2026
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	5.125%	5.125%
Repaid	$ 116
Exchanged	$ 147
Senior Notes | 4.000% Senior Notes due 2027
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	4.00%
Repaid	$ 153
Exchanged	$ 865
Senior Notes | Level 3 Financing, Inc. | 3.400% Senior Notes due 2027
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	3.40%
Repaid	$ 0
Exchanged	$ 668
Senior Notes | Level 3 Financing, Inc. | 3.875% Senior Notes due 2029
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	3.875%
Repaid	$ 0
Exchanged	$ 678
Senior Notes | Level 3 Financing, Inc. | 4.625% Senior Notes due 2027
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	4.625%
Repaid	$ 0
Exchanged	$ 606
Senior Notes | Level 3 Financing, Inc. | 4.250% Senior Notes due 2028
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	4.25%
Repaid	$ 0
Exchanged	$ 712
Senior Notes | Level 3 Financing, Inc. | 3.625% Senior Notes due 2029
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	3.625%
Repaid	$ 0
Exchanged	$ 458
Senior Notes | Level 3 Financing, Inc. | 3.750% Senior Notes due 2029
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	3.75%
Repaid	$ 0
Exchanged	$ 453