Loss Per Share - Calculation of Basic and Diluted Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Jul. 31, 2023	Apr. 30, 2023	Jan. 31, 2023	Jul. 31, 2022	Apr. 30, 2022	Jan. 31, 2022	Jul. 31, 2023	Jul. 31, 2022	Oct. 31, 2022
Numerator
Net loss attributable to FuelCell Energy, Inc.	$ (24,279)			$ (29,414)			$ (77,204)	$ (100,255)
Series B preferred stock dividends	(800)	$ (800)	$ (800)	(800)	$ (800)	$ (800)	(2,400)	(2,400)
Net loss attributable to common stockholders	$ (25,079)			$ (30,214)			$ (79,604)	$ (102,655)
Denominator
Weighted average common shares outstanding - basic	415,867,594			387,465,758			409,361,826	375,638,293
Weighted average common shares outstanding - diluted	415,867,594			387,465,758			409,361,826	375,638,293	375,638,293
Net loss to common stockholders per share - basic	$ (0.06)			$ (0.08)			$ (0.19)	$ (0.27)
Net loss to common stockholders per share - diluted	$ (0.06)			$ (0.08)			$ (0.19)	$ (0.27)	$ (0.27)
Series B Preferred Stock
Numerator
Series B preferred stock dividends	$ (800)			$ (800)			$ (2,400)	$ (2,400)