Investment Securities - Cost or Amortized Cost, Gross Unrealized Investment Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Common equity securities
Investment securities
Cost or Amortized Cost	$ 660.6	$ 236.3
Gross Unrealized Gains	26.7	16.1
Gross Unrealized Losses	(8.4)	0.0
Net Foreign Currency Gains (Losses)	(10.5)	(1.3)
Common equity securities, at fair value	668.4	251.1
MediaAlpha
Investment securities
Cost or Amortized Cost	0.0	0.0
Gross Unrealized Gains	168.6	261.6
Gross Unrealized Losses	0.0	0.0
Net Foreign Currency Gains (Losses)	0.0	0.0
Common equity securities, at fair value	168.6	261.6
Other long-term investments
Investment securities
Cost or Amortized Cost	1,340.8	1,186.7
Gross Unrealized Gains	271.1	239.0
Gross Unrealized Losses	(107.1)	(44.1)
Net Foreign Currency Gains (Losses)	(16.8)	(3.8)
Common equity securities, at fair value	$ 1,488.0	$ 1,377.8