Investment Securities - Cost or Amortized Cost, Gross Unrealized Investment Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Common equity securities
Investment securities
Cost or Amortized Cost	$ 236.3
Gross Unrealized Gains	16.1
Gross Unrealized Losses	0.0
Net Foreign Currency Gains (Losses)	(1.3)
Common equity securities, at fair value	251.1
MediaAlpha
Investment securities
Cost or Amortized Cost	0.0	$ 0.0
Gross Unrealized Gains	261.6	802.2
Gross Unrealized Losses	0.0	0.0
Net Foreign Currency Gains (Losses)	0.0	0.0
Common equity securities, at fair value	261.6	802.2
Other long-term investments
Investment securities
Cost or Amortized Cost	1,186.7	767.4
Gross Unrealized Gains	239.0	95.8
Gross Unrealized Losses	(44.1)	(78.1)
Net Foreign Currency Gains (Losses)	(3.8)	1.7
Common equity securities, at fair value	$ 1,377.8	$ 786.8

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

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=123594786&loc=SL75136599-209740

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

+ References

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=123583765&loc=SL75117546-209714

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