Operating Segment and Related Information - Geographic and Operating Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 444.8	$ 449.0
Income (loss) from operations	(26.8)	25.6
Interest expense	(21.3)	(18.8)
Loss from equity investees	2.5	5.9
Other income, net	2.8	3.4
(Loss) income from continuing operations before income taxes	(53.6)	4.3
Income tax benefit (expense)	12.6	(4.0)
Net loss	(101.0)	(6.3)
Net loss attributable to noncontrolling interest and redeemable noncontrolling interest	17.9	3.5
Net loss attributable to HC2 Holdings, Inc.	(83.1)	(2.8)
Less: Preferred dividends, deemed dividends and repurchase gains	0.4	(1.2)
Net loss attributable to common stock and participating preferred stockholders	(83.5)	(1.6)
Depreciation and Amortization	0.6	0.3
Capital Expenditures	6.1	3.3
Less: Loss from discontinued operations, net of tax	(60.0)	(6.6)
(Loss) income from continuing operations	(41.0)	0.3
Revenue	383.4	362.5
Loss on sale of subsidiary	39.3	0.0
Construction
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	176.5	192.1
Revenue	176.5	192.1
Energy
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	10.4	5.1
Revenue	8.7	4.8
Telecommunications
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	186.4	155.5
Revenue	186.4	155.5
Broadcasting
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	10.1	9.8
Revenue	10.1	9.8
Operating Segments | Construction
Revenues from External Customers and Long-Lived Assets [Line Items]
Income (loss) from operations	2.6	5.7
Depreciation and Amortization	2.6	3.9
Capital Expenditures	2.3	2.6
Revenue	176.5	192.1
Operating Segments | Energy
Revenues from External Customers and Long-Lived Assets [Line Items]
Income (loss) from operations	1.7	(0.4)
Depreciation and Amortization	2.1	1.4
Capital Expenditures	1.0	0.1
Revenue	10.4	5.1
Operating Segments | Telecommunications
Revenues from External Customers and Long-Lived Assets [Line Items]
Income (loss) from operations	0.1	0.6
Depreciation and Amortization	0.1	0.1
Revenue	186.4	155.5
Operating Segments | Insurance
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	63.8	88.8
Income (loss) from operations	(12.6)	34.4
Depreciation and Amortization	(5.9)	(6.5)
Capital Expenditures	0.1	0.2
Operating Segments | Life Science [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Income (loss) from operations	(3.2)	(1.8)
Operating Segments | Broadcasting
Revenues from External Customers and Long-Lived Assets [Line Items]
Income (loss) from operations	(2.9)	(3.3)
Depreciation and Amortization	1.7	1.4
Capital Expenditures	2.7	0.4
Revenue	10.1	9.8
Operating Segments | Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Income (loss) from operations	(1.0)	(0.1)
Corporate
Revenues from External Customers and Long-Lived Assets [Line Items]
Income (loss) from operations	(9.1)	(7.2)
Intersegment Eliminations
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	(2.4)	(2.3)
Income (loss) from operations	$ (2.4)	$ (2.3)