Investment Securities - Investment Holding Common Equities/ Other Investments/ MediaAlpha (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2021
Common equity securities
Debt and Equity Securities, FV-NI [Line Items]
Cost or Amortized Cost	$ 324.2	$ 236.3
Gross Unrealized Gains	32.7	16.1
Gross Unrealized Losses	(8.7)	0.0
Net Foreign Currency Gains (Losses)	(15.4)	(1.3)
Common equity securities, at fair value	332.8	251.1
Marketing Technology (MediaAlpha)
Debt and Equity Securities, FV-NI [Line Items]
Cost or Amortized Cost	0.0	0.0
Gross Unrealized Gains	148.2	261.6
Gross Unrealized Losses	0.0	0.0
Net Foreign Currency Gains (Losses)	0.0	0.0
Common equity securities, at fair value	148.2	261.6
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Cost or Amortized Cost	1,390.7	1,186.7
Gross Unrealized Gains	345.0	239.0
Gross Unrealized Losses	(90.0)	(44.1)
Net Foreign Currency Gains (Losses)	(23.0)	(3.8)
Common equity securities, at fair value	$ 1,622.7	$ 1,377.8