Commitments and Contingencies - Summary of Inventory Purchase Commitments (Details) $ in Millions	Mar. 31, 2026 USD ($)
Inventory purchase commitments
Total	$ 1,365.6
2026	1,297.6
Thereafter	$ 68.0

Inventory Purchase Obligation, To Be Paid, Remainder of Year One

No definition available.

Name:	ftnt_InventoryPurchaseObligationToBePaidRemainderOfYearOne
Namespace Prefix:	ftnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant