Investments (Fair Value Realized and Unrealized Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	$ (5.5)	$ (93.4)
ITV
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	45.1	(167.4)
Vodafone
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(37.4)	0.0
Lionsgate
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	34.1	(2.5)
Lacework
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(21.4)	0.0
Plume
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(17.5)	0.2
SMAs
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(14.5)	(8.9)
EdgeConneX
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	11.9	13.5
Other, net
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	$ (5.8)	$ 71.7