CenturyLink Merger - Narrative (Details) $ / shares in Units, $ in Millions	2 Months Ended	10 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares	Oct. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares	Nov. 01, 2017 USD ($) city dark_fiber $ / shares
Business Acquisition [Line Items]
Common stock, par value (in USD per share) | $ / shares
Goodwill	$ 10,837
Predecessor
Business Acquisition [Line Items]
Common stock, par value (in USD per share) | $ / shares			$ 0.01
Acquisition-related expenses	$ 28	$ 85	$ 15
Goodwill			$ 7,729
Level 3 Parent, LLC | Level 3 Communications, Inc.
Business Acquisition [Line Items]
Common stock, par value (in USD per share) | $ / shares				$ 0.01
Cash consideration per share (in dollars per share) | $ / shares				26.50
Level 3 Parent, LLC | CenturyLink
Business Acquisition [Line Items]
Common stock, par value (in USD per share) | $ / shares				$ 1.00
Stock conversion ratio				1.4286
Number of strands of dark fiber divested | dark_fiber				24
Number of cities connected by dark fiber | city				30
Goodwill				$ 10,821
Transaction costs				47
Level 3 Parent, LLC | CenturyLink | Restricted stock awards
Business Acquisition [Line Items]
Goodwill				1
Level 3 Parent, LLC | CenturyLink | Unsecured Debt
Business Acquisition [Line Items]
Long-term debt				$ 1,825
Stated interest rate (as a percent)				3.50%