Operating Segment and Related Information - Operating Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 243.8	$ 181.8	$ 415.6	$ 368.4
Total revenue	243.8	181.8	415.6	368.4
Income (loss) from operations	(7.7)	(8.9)	(18.6)	(22.5)
Interest expense	(12.4)	(19.1)	(33.8)	(38.3)
Loss on early extinguishment or restructuring of debt	(1.6)	(3.4)	(12.4)	(9.2)
Income (loss) from equity investees	0.2	(0.2)	(1.9)	(2.7)
Other income	0.4	64.6	3.8	66.1
(Loss) income from continuing operations before income taxes	(21.1)	33.0	(62.9)	(6.6)
Income tax expense	(2.6)	(12.0)	(3.7)	(2.3)
(Loss) income from continuing operations	(23.7)	21.0	(66.6)	(8.9)
(Loss) income from discontinued operations (including gain on disposal of $40.4 million and loss on disposal of $39.3 million for the six months ended June 30, 2021 and 2020, respectively)	(1.5)	7.5	50.4	(63.6)
Net (loss) income	(25.2)	28.5	(16.2)	(72.5)
Net income (loss) attributable to noncontrolling interest and redeemable noncontrolling interest	1.7	(15.4)	5.3	2.5
Net (loss) income attributable to HC2 Holdings, Inc.	(23.5)	13.1	(10.9)	(70.0)
Less: Preferred dividends and deemed dividends from conversions	0.2	0.4	0.6	0.8
Net (loss) income attributable to common stock and participating preferred stockholders	(23.7)	12.7	(11.5)	(70.8)
Depreciation and Amortization	4.8	4.5	8.7	8.8
Depreciation expense with cost of revenue	2.8	2.3	5.0	4.6
Total depreciation and amortization	7.6	6.8	13.7	13.4
Capital Expenditures	4.8	5.0	8.0	10.0
Gain (loss) on sale of subsidiary			40.4	(39.3)
Infrastructure
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	232.0	171.7	393.3	348.2
Total revenue	232.0	172.3	393.3	348.8
Life Sciences
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	1.2	0.0	1.2	0.0
Spectrum
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	10.6	9.5	21.1	19.6
Operating Segments | Infrastructure
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	232.0	172.3	393.3	348.8
Income (loss) from operations	2.2	4.5	4.4	7.1
Depreciation and Amortization	3.3	2.7	5.7	5.3
Capital Expenditures	3.9	1.1	5.5	3.4
Operating Segments | Life Sciences
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	1.2	0.0	1.2	0.0
Income (loss) from operations	(4.5)	(3.5)	(9.3)	(6.7)
Depreciation and Amortization	0.1	0.1	0.1	0.1
Capital Expenditures	0.3	0.1	0.5	0.1
Operating Segments | Spectrum
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	10.6	9.5	21.1	19.6
Income (loss) from operations	1.4	(1.2)	0.2	(4.1)
Depreciation and Amortization	1.4	1.7	2.9	3.4
Capital Expenditures	0.6	3.7	2.0	6.4
Operating Segments | Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Income (loss) from operations	(0.2)	(0.7)	(0.6)	(1.7)
Non-operating Corporate
Revenues from External Customers and Long-Lived Assets [Line Items]
Income (loss) from operations	(6.6)	(8.0)	(13.3)	(17.1)
Capital Expenditures	$ 0.0	$ 0.1	$ 0.0	$ 0.1