Liberty Broadband Corporation Quarterly report pursuant to Section 13 or 15(d)

Basis of Presentation (Details) $ in Millions		3 Months Ended		6 Months Ended
Basis of Presentation (Details) $ in Millions	Mar. 09, 2018	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
Liberty Media \| Affiliated Entity
Class of Stock [Line Items]
Reimbursable expenses		$ 2.2	$ 2.2	$ 4.5	$ 3.9
Liberty Ventures \| Series A common stock
Class of Stock [Line Items]
Shares redemption ratio	1
Liberty Ventures \| Series B common stock
Class of Stock [Line Items]
Shares redemption ratio	1