CenturyLink Merger - Additional Information (Details) $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Nov. 01, 2017 city dark_fiber
Business Acquisition [Line Items]
Goodwill	$ 11,132	$ 10,837
CenturyLink \| Level 3 Parent, LLC
Business Acquisition [Line Items]
Consideration transferred	19,600
Number of strands of dark fiber divested \| dark_fiber			24
Number of cities connected by dark fiber \| city			30
Goodwill	$ 11,190	$ 10,837

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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