Fair Value Measurements - Fair Value Disclosure of Asset and Liability Not Measured at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	$ 18.6	$ 21.7
Unfunded Commitments	0.0	0.1
Reported Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	107.3	97.5
Unfunded Commitments	0.0	0.1
Unfunded Commitments	266.1	250.1
Mezzanine Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	39.4	38.8
Unfunded Commitments	83.5	82.3
Real Estate Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.0	0.0
Senior Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	54.2	56.9
Unfunded Commitments	7.3	6.1
Leveraged Buyout
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	11.9	0.1
Unfunded Commitments	41.9	41.0
Distressed Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	17.5	16.1
Equity Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	4.7	5.7
Other
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	1.8	1.7
Unfunded Commitments	3.9	1.3
Measured at NAV
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	1.6	1.8
Measured at NAV \| Reported Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	183.0	176.0
Fair Value Using NAV	221.5	210.3
Unfunded Commitments	158.8	152.5
Fair Value Using NAV	1.6	1.8
Fair Value Using NAV	406.1	388.1
Measured at NAV \| Mezzanine Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	118.8	115.5
Fair Value Using NAV	120.1	115.8
Measured at NAV \| Real Estate Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	26.0	24.1
Measured at NAV \| Senior Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	21.2	21.1
Fair Value Using NAV	24.5	25.5
Measured at NAV \| Leveraged Buyout
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	7.1	6.5
Fair Value Using NAV	44.0	40.5
Measured at NAV \| Distressed Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	9.5	10.8
Measured at NAV \| Equity Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	11.9	10.7
Measured at NAV \| Other
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	9.9	8.8
Fair Value Using NAV	$ 11.5	$ 7.0

Fair Value, Alternative Investments, Entities That Calculate Net Asset Value, Unfunded Commitments

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Fair Value, Equity Method Investments, Entities That Calculate Net Asset Value, Unfunded Commitments

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Fair Value, Equity Securities FV-NI, Entities That Calculate Net Asset Value, Unfunded Commitments

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Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

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Fair value portion of investments accounted under the equity method.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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