Long-Term Debt and Credit Facilities - Revolving Letters of Credit and Senior Notes (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Letter of Credit \| Letter of Credit \| Uncommitted Revolving Letter of Credit Facility
Long-term Debt and Credit Facilities
Maximum borrowing capacity	$ 225,000,000
Lumen Technologies \| Letter of Credit \| Letter of Credit \| Uncommitted Revolving Letter of Credit Facility
Long-term Debt and Credit Facilities
Maximum borrowing capacity	225,000,000
Letters of credit outstanding	$ 97,000,000	$ 82,000,000
Lumen Technologies \| Senior Notes
Long-term Debt and Credit Facilities
Redemption price, percentage	101.00%
Level 3 Parent, LLC \| Letter of Credit \| Letter of Credit
Long-term Debt and Credit Facilities
Letters of credit outstanding	$ 18,000,000	23,000,000
Level 3 Parent, LLC \| Letter of Credit \| Letter of Credit \| Collateralized Debt Obligations
Long-term Debt and Credit Facilities
Letters of credit outstanding	$ 11,000,000	$ 18,000,000

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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