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

Basis of Presentation (Details) $ in Millions		3 Months Ended		9 Months Ended
Basis of Presentation (Details) $ in Millions	Mar. 09, 2018	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Liberty Media \| Affiliated Entity
Class of Stock [Line Items]
Reimbursable expenses		$ 2.3	$ 2.1	$ 6.8	$ 6.0
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