Investments (Fair Value Realized and Unrealized Losses) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	$ 71.5		$ (2.1)		$ (344.8)	$ (207.4)
Vodafone
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	35.7		0.0		(223.1)	0.0
Lacework
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(31.3)		0.0		(125.9)	0.0
EdgeConneX
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	65.9		16.4		79.9	58.9
Plume
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(4.0)		0.2		(55.2)	0.5
ITV
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(2.6)		(62.6)		(18.9)	(342.2)
Lionsgate
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(2.6)		(12.3)		17.3	(58.4)
Televisa Univision
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	12.1		26.2		4.7	58.0
SMAs
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	20.1		22.7		(1.2)	10.3
Other, net
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	$ (21.8)		$ 7.3		$ (22.4)	$ 65.5
Gain on sale of investment		$ 8.0		$ 12.0