v3.25.4
Fair Value Measurements - Fair Value using NAV and Unfunded Commitment by Asset Class (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Unfunded commitments, equity method limited liability investments $ 97.5 $ 91.3
Unfunded commitments, other equity interests at fair value 152.5 130.6
Fair value using NAV, equity securities at modified cost 21.7 22.5
Unfunded commitments, equity securities at modified cost 0.1 0.0
Unfunded commitments, investments in limited liability companies and limited partnerships 250.1 221.9
Mezzanine Debt    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Unfunded commitments, equity method limited liability investments 38.8 40.8
Unfunded commitments, other equity interests at fair value 82.3 67.0
Real Estate    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Unfunded commitments, equity method limited liability investments 0.0 0.0
Unfunded commitments, other equity interests at fair value 0.0 0.0
Senior Debt    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Unfunded commitments, equity method limited liability investments 56.9 48.2
Unfunded commitments, other equity interests at fair value 6.1 8.4
Leveraged Buyout    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Unfunded commitments, equity method limited liability investments 0.1 0.6
Unfunded commitments, other equity interests at fair value 41.0 30.4
Secondary Transactions    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Unfunded commitments, equity method limited liability investments 1.6 1.6
Unfunded commitments, other equity interests at fair value 1.0 1.6
Distressed Debt    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Unfunded commitments, equity method limited liability investments 0.0 0.0
Unfunded commitments, other equity interests at fair value 16.1 15.0
Growth Equity    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Unfunded commitments, other equity interests at fair value 5.7 8.0
Other    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Unfunded commitments, equity method limited liability investments 0.1 0.1
Unfunded commitments, other equity interests at fair value 0.3 0.2
Fair Value Measured at Net Asset Value Per Share    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Fair value using NAV, equity method limited liability investments 176.0 186.3
Fair value using NAV, other equity interests at fair value 210.3 183.6
Fair value using NAV, equity securities at modified cost 1.8 1.8
Total 388.1 371.7
Fair Value Measured at Net Asset Value Per Share | Mezzanine Debt    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Fair value using NAV, equity method limited liability investments 115.5 116.7
Fair value using NAV, other equity interests at fair value 115.8 116.9
Fair Value Measured at Net Asset Value Per Share | Real Estate    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Fair value using NAV, equity method limited liability investments 24.1 27.3
Fair value using NAV, other equity interests at fair value 0.1 0.0
Fair Value Measured at Net Asset Value Per Share | Senior Debt    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Fair value using NAV, equity method limited liability investments 21.1 19.1
Fair value using NAV, other equity interests at fair value 25.5 26.3
Fair Value Measured at Net Asset Value Per Share | Leveraged Buyout    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Fair value using NAV, equity method limited liability investments 6.5 7.5
Fair value using NAV, other equity interests at fair value 40.5 19.2
Fair Value Measured at Net Asset Value Per Share | Secondary Transactions    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Fair value using NAV, equity method limited liability investments 1.9 5.5
Fair value using NAV, other equity interests at fair value 1.3 2.4
Fair Value Measured at Net Asset Value Per Share | Distressed Debt    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Fair value using NAV, equity method limited liability investments 1.4 4.4
Fair value using NAV, other equity interests at fair value 10.8 11.7
Fair Value Measured at Net Asset Value Per Share | Growth Equity    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Fair value using NAV, other equity interests at fair value 10.7 7.0
Fair Value Measured at Net Asset Value Per Share | Other    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Fair value using NAV, equity method limited liability investments 5.5 5.8
Fair value using NAV, other equity interests at fair value $ 5.6 $ 0.1