Long-Term Debt and Credit Facilities - Additional Information (Details)		3 Months Ended
	Mar. 22, 2024 USD ($) Agreement	Mar. 31, 2024 USD ($) indenture	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Long-term Debt and Credit Facilities
Number of debt agreements | Agreement	2
Face amount		$ 11,982,000,000
Reduction in total debt maturities		$ 10,200,000,000
Long-term debt, weighted average interest rate		7.73%		6.23%
Reduction in debt resulting from debt extinguishment		$ 492,000,000
Net gain on extinguishment of debt		275,000,000	$ 609,000,000
Payment for lender fees		209,000,000
Payment for third-party costs		174,000,000
Debt instrument, capitalized lender fees		52,000,000
Third party costs capitalized		$ 62,000,000
Last Day of Each Fiscal Quarter
Long-term Debt and Credit Facilities
Maximum total net leverage ratio		5.75
Gain (Loss) on Extinguishment of Debt
Long-term Debt and Credit Facilities
Debt instrument, lender fees		$ 157,000,000
Operating Expense
Long-term Debt and Credit Facilities
Debt instrument, third-party costs		112,000,000
Revolving Credit Facility
Long-term Debt and Credit Facilities
Maximum borrowing capacity		1,000,000,000		$ 2,200,000,000
Borrowings		0
Remaining borrowing capacity		715,000,000
Letter of Credit
Long-term Debt and Credit Facilities
Borrowings		$ 241,000,000
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%
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%
Level 3 Financing, Inc. | SOFR
Long-term Debt and Credit Facilities
Floor rate (as a percent)		2.00%
Basis spread (as a percent)		6.56%
Level 3 Financing, Inc. | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)		5.56%
Series A Revolving Credit Facility
Long-term Debt and Credit Facilities
Maximum borrowing capacity		$ 489,000,000
Series A Revolving Credit Facility | Financial Guarantee
Long-term Debt and Credit Facilities
Guaranteed amount		150,000,000
Series B Revolving Credit Facility
Long-term Debt and Credit Facilities
Maximum borrowing capacity		467,000,000
Series B Revolving Credit Facility | Financial Guarantee
Long-term Debt and Credit Facilities
Guaranteed amount		150,000,000
Uncommitted Revolving Letter of Credit Facility | Letter of Credit
Long-term Debt and Credit Facilities
Maximum borrowing capacity		225,000,000
Tranche B 2027 Term Loan | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Long-term debt, gross		$ 12,000,000		2,411,000,000
Tranche B 2027 Term Loan | Level 3 Financing, Inc. | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		1.75%
Senior Notes
Long-term Debt and Credit Facilities
Number of indentures | indenture		4
Redemption price (as a percent)		101.00%
Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Redemption price (as a percent)		101.00%
Senior Notes | First Lien Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Face amount	$ 1,575,000,000
Proceeds from debt issuance	1,325,000,000	$ 1,325,000,000
Non-cash fee	50,000,000
Long-term debt, gross		$ 3,846,000,000		925,000,000
Senior Notes | First Lien Notes | Level 3 Financing, Inc. | Maximum
Long-term Debt and Credit Facilities
Stated interest rate		11.00%
Senior Notes | First Lien Notes | Level 3 Financing, Inc. | Minimum
Long-term Debt and Credit Facilities
Stated interest rate		10.50%
Senior Notes | 4.000% Senior Secured Notes Due 2027
Long-term Debt and Credit Facilities
Face amount	$ 200,000,000
Stated interest rate	4.00%	4.00%
Long-term debt, gross		$ 0		1,250,000,000
Line of Credit | Revolving Credit Facility
Long-term Debt and Credit Facilities
Long-term debt, gross		$ 0
Line of Credit | Series A Revolving Credit Facility
Long-term Debt and Credit Facilities
Long-term debt, weighted average interest rate		8.05%
Floor rate (as a percent)		2.00%
Long-term debt, gross		$ 0		0
Line of Credit | Series A Revolving Credit Facility | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		4.00%
Line of Credit | Series A Revolving Credit Facility | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)		3.00%
Line of Credit | Series B Revolving Credit Facility
Long-term Debt and Credit Facilities
Long-term debt, weighted average interest rate		10.05%
Floor rate (as a percent)		2.00%
Long-term debt, gross		$ 0		$ 0
Line of Credit | Series B Revolving Credit Facility | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		6.00%
Line of Credit | Series B Revolving Credit Facility | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)		5.00%
Term Loan | Term Loan A
Long-term Debt and Credit Facilities
Face amount		$ 372,000,000
Long-term debt, weighted average interest rate		11.329%		7.47%
Long-term debt, gross		$ 372,000,000		$ 0
Term Loan | Term Loan A | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		6.00%
Term Loan | Term Loan B
Long-term Debt and Credit Facilities
Long-term debt, weighted average interest rate		7.695%		7.72%
Debt instrument periodic payment (as a percent)		0.25%
Long-term debt, gross		$ 57,000,000		$ 3,891,000,000
Term Loan | Term Loan B | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		2.25%
Term Loan | Term Loan B-1
Long-term Debt and Credit Facilities
Face amount		$ 1,625,000,000
Long-term debt, weighted average interest rate		7.739%
Long-term debt, gross		$ 1,625,000,000		0
Term Loan | Term Loan B-1 | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		2.35%
Term Loan | Term Loan B-1 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Face amount		$ 1,199,000,000
Long-term debt, weighted average interest rate		11.889%
Long-term debt, gross		$ 1,199,000,000		0
Term Loan | Term Loan B-1 | Level 3 Financing, Inc. | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		6.56%
Term Loan | Term Loan B-2
Long-term Debt and Credit Facilities
Face amount		$ 1,625,000,000
Long-term debt, weighted average interest rate		7.739%
Long-term debt, gross		$ 1,625,000,000		0
Term Loan | Term Loan B-2 | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		2.35%
Term Loan | Term Loan B-2 | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Face amount		$ 1,199,000,000
Long-term debt, weighted average interest rate		11.889%
Long-term debt, gross		$ 1,199,000,000		$ 0
Term Loan | Term Loan B-2 | Level 3 Financing, Inc. | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		6.56%
Term Loan | Tranche B 2027 Term Loan | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Long-term debt, weighted average interest rate		7.195%		7.22%
Long-term debt, gross		$ 12,000,000
Term Loan | Superpriority Secured Term Loan Facility
Long-term Debt and Credit Facilities
Face amount		$ 377,000,000
Floor rate (as a percent)		2.00%
Debt instrument periodic payment (as a percent)		1.25%
Term Loan | Superpriority Secured Term Loan Facility | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		6.00%
Term Loan | Superpriority Secured Term Loan Facility | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)		5.00%
Term Loan | Superpriority Term Loan B
Long-term Debt and Credit Facilities
Floor rate (as a percent)		0.00%
Term Loan | Superpriority Term Loan B | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		2.35%
Term Loan | Superpriority Term Loan B | Base Rate
Long-term Debt and Credit Facilities
Basis spread (as a percent)		1.35%
Line of Credit and Term Loan | Fiscal Quarter Ending After December 31, 2024
Long-term Debt and Credit Facilities
Maximum total net leverage ratio		5.50
Line of Credit and Term Loan | Fiscal Quarter Ending After December 31, 2025
Long-term Debt and Credit Facilities
Maximum total net leverage ratio		5.25
Line of Credit and Term Loan | Minimum
Long-term Debt and Credit Facilities
Interest coverage ratio		2.00
Line of Credit and Term Loan | Other Facilities
Long-term Debt and Credit Facilities
Long-term debt, gross		$ 0		$ 1,399,000,000
Line of Credit and Term Loan | Other Facilities | SOFR
Long-term Debt and Credit Facilities
Basis spread (as a percent)		2.00%