Long-Term Debt and Credit Facilities - Lumen Credit Agreements and Level 3 Credit Agreement (Details) - USD ($) $ in Millions		12 Months Ended
	Mar. 22, 2024	Dec. 31, 2024	Dec. 31, 2023
Long-term Debt and Credit Facilities
Debt instrument, face amount		$ 11,925
Series A Revolving Credit Facility
Long-term Debt and Credit Facilities
Maximum borrowing capacity	$ 489	$ 489
Series A Revolving Credit Facility | Line of Credit
Long-term Debt and Credit Facilities
Floor interest rate (as a percent)	2.00%
Basis spread (as a percent)		4.00%
Long-term debt, gross		$ 0	$ 0
Series A Revolving Credit Facility | Line of Credit | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)	4.00%
Series A Revolving Credit Facility | Line of Credit | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)	3.00%
Series B Revolving Credit Facility
Long-term Debt and Credit Facilities
Maximum borrowing capacity	$ 467	$ 465
Series B Revolving Credit Facility | Line of Credit
Long-term Debt and Credit Facilities
Floor interest rate (as a percent)	2.00%
Basis spread (as a percent)		6.00%
Long-term debt, gross		$ 0	$ 0
Series B Revolving Credit Facility | Line of Credit | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)	6.00%
Series B Revolving Credit Facility | Line of Credit | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)	5.00%
Lumen TLA | Term Loan
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 377
Floor interest rate (as a percent)	2.00%
Debt instrument periodic payment (as a percent)	1.25%
Lumen TLA | Term Loan | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)	6.00%
Lumen TLA | Term Loan | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)	5.00%
TLB Credit Agreement | Term Loan
Long-term Debt and Credit Facilities
Floor interest rate (as a percent)	0.00%
Debt instrument periodic payment (as a percent)	0.25%
TLB Credit Agreement | Term Loan | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)	2.35%
TLB Credit Agreement | Term Loan | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)	1.35%
Lumen TLB-1 | Term Loan
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 1,600
Lumen TLB-2 | Term Loan
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 1,600
New Level 3 Credit Agreement | Level 3 Financing, Inc. | Prepaid on or Prior to the 12-Month Anniversary of the Effective Date
Long-term Debt and Credit Facilities
Prepayment premium, rate	2.00%
New Level 3 Credit Agreement | Level 3 Financing, Inc. | Prepaid After the 12-Month Anniversary and on or Prior to the 24-Month Anniversary of the Effective Date
Long-term Debt and Credit Facilities
Prepayment premium, rate	1.00%
New Level 3 Credit Agreement | Term Loan | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Floor interest rate (as a percent)	2.00%
New Level 3 Credit Agreement | Term Loan | SOFR | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Basis spread (as a percent)	6.56%
New Level 3 Credit Agreement | Term Loan | Base Rate | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Basis spread (as a percent)	5.56%
Secured Term B-1 Loan | Term Loan | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 1,200
Secured Term B-2 Loan | Term Loan | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 1,200