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Equity Method Eligible Investments - Carrying Value and Ownership Percentages (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	May 07, 2020	May 06, 2020	May 31, 2019
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	$ 1,488.0	$ 1,377.8
Kudu
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	695.9	669.5
MediaAlpha
Investments in and Advances to Affiliates [Line Items]
Common equity securities, at fair value	168.6	261.6
PassportCard/DavidShield
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	135.0	120.0
Elementum Holdings, L.P.
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	30.0	45.0
Other Investment Sector
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	84.4	109.3
Equity Method Investments
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	$ 0.0	$ 17.8
Kudu's Participation Contracts \| Minimum
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	4.10%	3.20%
Kudu's Participation Contracts \| Maximum
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	30.00%	32.00%
MediaAlpha
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	27.10%	28.00%
PassportCard/DavidShield
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	53.80%	53.80%	53.80%	50.00%
Elementum Holdings, L.P.
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	29.70%	29.70%			30.00%