Long-Term Debt and Credit Facilities - Credit Facilities Transactions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Long-term Debt and Credit Facilities
Net loss (gain) on early retirement of debt	$ 236	$ (3)	$ 271	$ (278)
Level 3 Financing, Inc. | Term Loan B-3 | Term Loan
Long-term Debt and Credit Facilities
Long-term debt, gross	$ 2,400		2,400		$ 0
Net loss (gain) on early retirement of debt			$ 35