Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 433.4	$ 299.3
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation	66.1	62.3
Amortization of deferred contract costs	78.0	72.0
Depreciation and amortization	35.8	28.6
Amortization of investment discounts	(10.3)	(12.2)
Other	(35.5)	9.9
Changes in operating assets and liabilities, net of impact of business combinations:
Accounts receivable—net	303.9	405.6
Inventory	(34.1)	36.5
Prepaid expenses and other current assets	3.4	(0.1)
Deferred contract costs	(91.3)	(66.5)
Deferred tax assets	(30.0)	(73.9)
Other assets	1.5	(6.2)
Accounts payable	24.6	(61.6)
Accrued liabilities	63.7	105.0
Accrued payroll and compensation	(8.2)	(27.4)
Deferred revenue	57.0	54.8
Other liabilities	5.3	4.3
Net cash provided by operating activities	863.3	830.4
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investments	(503.0)	(436.1)
Sales of investments	2.8	0.0
Maturities of investments	466.9	393.4
Purchases of property and equipment	(66.5)	(221.9)
Payments made in connection with business combinations, net of cash acquired	(11.2)	(5.7)
Other	0.2	0.0
Net cash used in investing activities	(110.8)	(270.3)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	20.2	13.4
Taxes paid related to net share settlement of equity awards	(52.9)	(42.9)
Other	0.0	(0.8)
Net cash used in financing activities	(32.7)	(30.3)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	0.9	(1.4)
NET INCREASE IN CASH AND CASH EQUIVALENTS	720.7	528.4
CASH AND CASH EQUIVALENTS—Beginning of period	2,875.9	1,397.9
CASH AND CASH EQUIVALENTS—End of period	3,596.6	1,926.3
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes—net	26.8	31.1
Operating lease liabilities arising from obtaining right-of-use assets	6.7	15.0
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Transfers of evaluation units and equipment from inventory to property and equipment	6.2	6.5
Liability for purchase of property and equipment	$ 25.1	$ 27.6

Transfers of Evaluation Units from Inventory to Property and Equipment

No definition available.

Name:	ftnt_TransfersofEvaluationUnitsfromInventorytoPropertyandEquipment
Namespace Prefix:	ftnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.