Investment Securities - Investment Holding Common Equities/ Other Investments/ MediaAlpha (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2022	Dec. 31, 2021
Common equity securities
Debt and Equity Securities, FV-NI [Line Items]
Cost or Amortized Cost	$ 274.3	$ 236.3
Gross Unrealized Gains	20.8	16.1
Gross Unrealized Losses	(1.9)	0.0
Net Foreign Currency Gains (Losses)	(3.1)	(1.3)
Common equity securities, at fair value	290.1	251.1
Marketing Technology (MediaAlpha)
Debt and Equity Securities, FV-NI [Line Items]
Cost or Amortized Cost	0.0	0.0
Gross Unrealized Gains	280.4	261.6
Gross Unrealized Losses	0.0	0.0
Net Foreign Currency Gains (Losses)	0.0	0.0
Common equity securities, at fair value	280.4	261.6
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Cost or Amortized Cost	1,187.0	1,186.7
Gross Unrealized Gains	291.6	239.0
Gross Unrealized Losses	(52.8)	(44.1)
Net Foreign Currency Gains (Losses)	2.7	(3.8)
Common equity securities, at fair value	$ 1,428.5	$ 1,377.8

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117546-209714

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