Long-Term Debt and Credit Facilities - Senior Notes Issuance and Senior Notes Tender Offers (Details) - USD ($) $ in Millions	Jun. 30, 2026	May 21, 2026	Mar. 31, 2026	Feb. 02, 2026	Jan. 09, 2026
Long-term Debt and Credit Facilities
Repurchased face amount	$ 14		$ 5	$ 4,765
Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Repurchased face amount		$ 766			$ 607
Level 3 Financing, Inc. \| 3.750% Senior Notes due 2029
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	3.75%
Level 3 Financing, Inc. \| Senior Notes \| 7.500% Senior Notes due 2037
Long-term Debt and Credit Facilities
Debt instrument, face amount		$ 1,000
Stated interest rate (as a percent)		7.50%
Level 3 Financing, Inc. \| Senior Notes \| 4.250% Senior Notes due 2028
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		4.25%
Repurchased face amount		$ 172
Level 3 Financing, Inc. \| Senior Notes \| 3.625% Senior Notes due 2029
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		3.625%
Repurchased face amount		$ 292
Level 3 Financing, Inc. \| Senior Notes \| 3.750% Senior Notes due 2029
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)		3.75%
Repurchased face amount	$ 3	$ 302