Basic and Diluted Income Per Common Share - Basic Income (Loss) Per Common Share to Diluted Income (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
(Loss) income from continuing operations	$ (41.0)	$ 0.3
Net loss attributable to noncontrolling interest and redeemable noncontrolling interest	2.6	2.4
Net loss attributable to noncontrolling interest and redeemable noncontrolling interest	(38.4)	2.7
Less: Preferred dividends, deemed dividends and repurchase gains	0.4	(1.2)
(Loss) income from continuing operations attributable to HC2 common stockholders	(38.8)	3.9
Loss from discontinued operations	(60.0)	(6.6)
Net loss attributable to noncontrolling interest and redeemable noncontrolling interest	15.3	1.1
Loss from discontinued operations, net of tax and noncontrolling interest	(44.7)	(5.5)
Net loss attributable to common stock and participating preferred stockholders	$ (83.5)	$ (1.6)
Participating shares at end of period:
Weighted-average Common stock outstanding (in shares)	45.9	44.8
Unvested restricted stock (in shares)	0.0	0.4
Preferred stock (as-converted basis) (in shares)	0.0	2.2
Total (in shares)	45.9	47.4
Percentage of (loss) income allocated to:
Common stock	100.00%	94.50%
Unvested restricted stock	0.00%	0.80%
Preferred stock	0.00%	4.60%
Earnings allocable to common shares, diluted:
Effect of assumed shares under treasury stock method for stock options and restricted shares and if-converted method for convertible instruments	$ 0.0	$ (1.6)
Net (loss) income from continuing operations attributable to common stock, diluted	(38.8)	2.1
Net (loss) income from discontinued operations attributable to common stock, diluted	(44.7)	(5.2)
Net loss attributable to common stock and participating preferred stockholders, diluted	$ (83.5)	$ (3.1)
Denominator for basic and dilutive earnings per share:
Weighted-average Common stock outstanding (in shares)	45.9	44.8
Effect of assumed shares under treasury stock method for stock options and restricted shares and if-converted method for convertible instruments (in shares)	0.0	14.9
Diluted (in shares)	45.9	59.7
Net (loss) income from continuing operations attributable to common stock, basic	$ (38.8)	$ 3.7
Net loss from discontinued operations attributable to common stock, basic and diluted	(44.7)	(5.2)
Net loss attributable to common stock and participating preferred stockholders, basic and diluted	$ (83.5)	$ (1.5)
(Loss) income per share - continuing operations
Net (loss) income attributable to continuing operations - basic (in usd per share)	$ (0.85)	$ 0.08
Net (loss) income attributable to participating security holders - diluted (in dollars per share)	(0.85)	0.04
Loss per share - discontinued operations
Basic (in usd per share)	(0.97)	(0.12)
Diluted (in usd per share)	(0.97)	(0.09)
Loss per share - Net loss attributable to common stock and participating preferred stockholders
Basic (in usd per share)	(1.82)	(0.03)
Diluted (in usd per share)	$ (1.82)	$ (0.05)
Loss on sale of subsidiary	$ (39.3)	$ 0.0