Investments (Fair Value Realized and Unrealized Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	$ (302.1)	$ 735.0	$ 35.8
ITV
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(233.9)	15.3	(217.1)
Pax8
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	79.3	0.0	0.0
Lionsgate
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(69.2)	33.9	4.0
SMAs
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(49.1)	(10.1)	5.2
EdgeConneX
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	43.4	28.9	33.1
Plume Design, Inc. (Plume)
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(34.8)	133.9	29.6
Skillz Inc. (Skillz)
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(34.7)	(100.4)	238.0
TiBiT Communications, Inc. (TiBiT)
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	26.4	0.0	0.0
Lacework
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(26.3)	223.9	1.1
Televisa Univision
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	23.1	301.6	0.0
Aviatrix Systems, Inc. (Aviatrix)
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	0.0	65.4	0.0
Other, net
Net Investment Income [Line Items]
Realized and unrealized gains (losses)	(26.3)	42.6	$ (58.1)
Gain on sale of investment	$ 15.7	$ 12.9