Computation of Weighted Average Basic and Diluted Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Income (loss) from operations	$ 11.4	$ (1.8)	$ 9.1	$ (15.0)
Less: loss attributable to noncontrolling interest	(0.3)	(0.3)	(0.4)	(0.7)
Net income (loss) attributable to GlassBridge Enterprises, Inc.	$ 11.7	$ (1.5)	$ 9.5	$ (14.3)
Weighted average number of common shares outstanding during the period - basic and diluted (in thousands)	25.2	25.2	25.2	25.2
Net income (loss)	$ 464.29	$ (59.37)	$ 376.98	$ (567.06)
Anti-dilutive shares excluded from calculation	0.0	0.0	0.0	0.0