Investment Securities - Cost or Amortized Cost, Gross Unrealized Investment Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
MediaAlpha
Investment securities
Cost or Amortized Cost	$ 0.0	$ 0.0
Gross Unrealized Gains	802.2	180.0
Gross Unrealized Losses	0.0	0.0
Net Foreign Currency Gains	0.0	0.0
Common equity securities, at fair value	802.2	180.0
Common equity securities
Investment securities
Cost or Amortized Cost	0.0	553.3
Gross Unrealized Gains	0.0	130.6
Gross Unrealized Losses	0.0	0.0
Net Foreign Currency Gains	0.0	0.0
Common equity securities, at fair value	0.0	683.9
Other long-term investments
Investment securities
Cost or Amortized Cost	767.4	667.4
Gross Unrealized Gains	95.8	75.2
Gross Unrealized Losses	(78.1)	(64.1)
Net Foreign Currency Gains	1.7	(2.2)
Common equity securities, at fair value	$ 786.8	$ 676.3

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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Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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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=120269885&loc=SL75117546-209714

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

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Equity Securities, FV-NI, Foreign Currency Losses

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