Long-Term Debt and Credit Facilities - Transaction Support Agreement Transactions - New Debt Issuances (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2024	Nov. 30, 2024	Sep. 24, 2024
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 11,925
Term Loan
Long-term Debt and Credit Facilities
Debt instrument, periodic payment	66
Senior Notes
Long-term Debt and Credit Facilities
Debt instrument, face amount		$ 393	$ 848
Term Loan A | Term Loan
Long-term Debt and Credit Facilities
Debt instrument, face amount	357
Term Loan B-1 | Term Loan
Long-term Debt and Credit Facilities
Debt instrument, face amount	1,606
Term Loan B-1 | Term Loan | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Debt instrument, face amount	1,199
Term Loan B-2 | Term Loan
Long-term Debt and Credit Facilities
Debt instrument, face amount	1,606
Term Loan B-2 | Term Loan | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 1,199
4.125% Superpriority Notes due 2029-2030 | Senior Notes
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	4.125%
Debt instrument, face amount	$ 808
10.500% First Lien Notes due 2029 | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	10.50%
Debt instrument, face amount	$ 668
11.000% First Lien Notes due 2029 | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	11.00%
Debt instrument, face amount	$ 1,575
4.875% Second Lien Notes due 2029 | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	4.875%
Debt instrument, face amount	$ 606
10.750% First Lien Notes due 2030 | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	10.75%
Debt instrument, face amount	$ 678
4.500% Second Lien Notes due 2030 | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	4.50%
Debt instrument, face amount	$ 712
3.875% Second Lien Notes due 2030 | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	3.875%
Debt instrument, face amount	$ 458
4.000% Second Lien Notes due 2031 | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Stated interest rate (as a percent)	4.00%
Debt instrument, face amount	$ 453
11.000% First Lien Notes Due 2029- One | Senior Notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Debt instrument, face amount	$ 1,375