Discontinued Operations - Narrative (Details) - USD ($) $ in Millions					3 Months Ended					9 Months Ended
	Jul. 01, 2021	Jan. 15, 2021	Oct. 31, 2020	Feb. 28, 2020	Sep. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accumulated other comprehensive income					$ 3.2		$ 396.9			$ 3.2
Cash and cash equivalents					55.5		43.8	$ 28.2		55.5	$ 28.2	$ 23.3
Investments					49.9		55.4			49.9
Gain (loss) on sale of subsidiary										(159.9)	(39.3)
Loss on disposal of subsidiary					334.0			0.0		334.0	(22.1)
Repayments of long-term debt										454.8	155.3
Foreign currency translation adjustment					1.2			0.5		2.4	(3.5)
Infrastructure
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Station license					0.7					$ 0.7
GMSL
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary						$ 1.2	2.4		$ (39.3)
Loss on disposal of subsidiary									$ 31.3
GMSL | Revolving Credit Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt				$ 15.0
GMSL | 11.5% Senior Secured Notes
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, amount redeemed				$ 76.9
Interest rate				11.50%
GMSL | Secured Indenture
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, amount redeemed				$ 76.9
Beyond6 | 11.5% Senior Secured Notes
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt		$ 27.9
Beyond6 | 2020 Revolving Credit Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt		15.0
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary					$ (200.3)			$ 0.0			$ (39.3)
Discontinued Operations | CIG
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beneficial ownership interest					6.60%					6.60%
Gain (loss) on sale of subsidiary	$ (200.8)
Discontinued Operations | CIG | Insurance
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Segment book value	544.0
Accumulated other comprehensive income	344.0
Cash and cash equivalents	62.5
Investments	$ 26.7
Discontinued Operations | GMSL
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary				(39.3)		$ 1.2	$ 2.4
Loss on disposal of subsidiary				31.3
Discontinued Operations | GMSL | Revolving Credit Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt				$ 15.0
Discontinued Operations | ICS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary			$ 0.9
Foreign currency translation adjustment			$ 8.2
Discontinued Operations | Beyond6
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary		$ 39.2			$ 0.5