Net Income Per Share , Calculation of Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Earnings Per Share [Line Items]
Net income including non-controlling interests	$ 247.7	$ 138.3
Net loss attributable to non-controlling interests	0.0	(0.1)
Net income	$ 247.7	$ 138.4
Basic shares:
Weighted-average common shares outstanding-basic (in shares)	783.2	803.4
Diluted shares:
Weighted-average common shares outstanding-basic (in shares)	783.2	803.4
Effect of potentially dilutive securities:
Weighted-average shares used to compute diluted net income per share (in shares)	793.4	820.8
Net income per share attributable to Fortinet, Inc.:
Basic (in dollars per share)	$ 0.32	$ 0.17
Diluted (in dollars per share)	$ 0.31	$ 0.17
RSUs
Effect of potentially dilutive securities:
RSUs and stock options (in shares)	3.6	8.6
Stock options
Effect of potentially dilutive securities:
RSUs and stock options (in shares)	6.6	8.8