Long-Term Debt and Credit Facilities - New Issuances (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Nov. 27, 2020	Aug. 12, 2020	Jun. 15, 2020	Jan. 24, 2020	Jan. 15, 2020	Dec. 16, 2019	Nov. 29, 2019	Sep. 25, 2019
Long-term Debt and Credit Facilities
Repayments of debt	$ 6,200,000,000	$ 3,600,000,000
Lumen Technologies
Long-term Debt and Credit Facilities
Repayments of debt	1,300,000,000	340,000,000
Lumen Technologies | Senior Notes
Long-term Debt and Credit Facilities
Repayments of debt	$ 78,000,000
Lumen Technologies | Senior Notes | 4.500% Senior Notes Due 2029
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance			$ 1,000,000,000.0
Interest rate, stated percentage			4.50%
Lumen Technologies | Senior Notes | 4.000% Senior Secured Notes Due 2027
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance						$ 1,250,000,000
Interest rate, stated percentage	4.00%					4.00%
Lumen Technologies | Senior Notes | 5.125% Senior Notes Due 2026
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance								$ 1,250,000,000
Interest rate, stated percentage								5.125%
Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Repayments of debt		2,300,000,000
Level 3 Financing, Inc. | Senior Notes
Long-term Debt and Credit Facilities
Repayments of debt	$ 2,000,000,000.0
Level 3 Financing, Inc. | Senior Notes | 5.75% Senior Notes Due 2022
Long-term Debt and Credit Facilities
Repurchased face amount										$ 400,000,000
Level 3 Financing, Inc. | Senior Notes | 3.625% Senior Notes Due 2029
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance				$ 840,000,000
Interest rate, stated percentage				3.625%
Level 3 Financing, Inc. | Senior Notes | 4.250% Senior Secured Notes Due 2028
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance					$ 1,200,000,000
Interest rate, stated percentage					4.25%
Level 3 Financing, Inc. | Senior Notes | 3.400% Senior Notes Due 2027
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance									$ 750,000,000
Interest rate, stated percentage									3.40%
Level 3 Financing, Inc. | Senior Notes | 3.875% Senior Secured Notes Due 2029
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance									$ 750,000,000
Interest rate, stated percentage									3.875%
Level 3 Financing, Inc. | Senior Notes | Tranche B 2024 Term Loan
Long-term Debt and Credit Facilities
Repurchased face amount									$ 4,611,000,000
Level 3 Financing, Inc. | Senior Notes | Tranche B 2027 Term Loan
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance									$ 3,111,000,000
Level 3 Financing, Inc. | Senior Notes | 4.625% Senior Notes Due 2027
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance										$ 1,000,000,000.0
Interest rate, stated percentage										4.625%
Qwest Corporation | Senior Notes
Long-term Debt and Credit Facilities
Repayments of debt	$ 2,800,000,000
Qwest Corporation | Senior Notes
Long-term Debt and Credit Facilities
Repurchased face amount							$ 1,100,000,000
Level 3 Parent, LLC
Long-term Debt and Credit Facilities
Repayments of debt		$ 600,000,000
Level 3 Parent, LLC | Senior Notes | 5.75% Senior Notes Due 2022
Long-term Debt and Credit Facilities
Repurchased face amount										$ 600,000,000