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Investments Investment Income (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Net Investment Income |  |  |  |  |
Gross Investment Income, Operating |  | $ 501.4 | $ 548.2 | $ 1,623.7 | $ 1,643.5
Less Investment Expenses |  | 21.8 | 17.5 | 64.5 | 48.3
Less Investment Income on PFA Assets |  | 2.8 | 2.9 | 8.5 | 8.8
Net Investment Income |  | 476.8 | 527.8 | 1,550.7 | 1,586.4
Fixed Maturity Securities |  |  |  |  |
Net Investment Income |  |  |  |  |
Gross Investment Income, Operating |  | 419.1 | 465.4 | 1,360.2 | 1,388.5
Derivatives |  |  |  |  |
Net Investment Income |  |  |  |  |
Gross Investment Income, Operating |  | 3.7 | 8.1 | 5.6 | 25.0
Mortgage Loans |  |  |  |  |
Net Investment Income |  |  |  |  |
Gross Investment Income, Operating |  | 22.0 | 22.0 | 65.7 | 66.6
Policy Loans |  |  |  |  |
Net Investment Income |  |  |  |  |
Gross Investment Income, Operating |  | 5.3 | 5.7 | 16.2 | 16.3
Perpetual Preferred Securities |  |  |  |  |
Net Investment Income |  |  |  |  |
Gross Investment Income, Operating |  | (0.1) | 0.0 | 0.7 | 0.3
Private Equity Partnerships |  |  |  |  |
Net Investment Income |  |  |  |  |
Gross Investment Income, Operating | [1] | 21.7 | 19.6 | 65.3 | 72.6
Unrealized Gain (Loss) on Investments |  | 28.8 | 25.3 | 86.4 | 87.6
Management Fee Expense |  | (7.1) | (5.7) | (21.1) | (15.0)
Other Long-term Investments |  |  |  |  |
Net Investment Income |  |  |  |  |
Gross Investment Income, Operating |  | 4.2 | 3.4 | 23.4 | 8.5
Short-term Investments |  |  |  |  |
Net Investment Income |  |  |  |  |
Gross Investment Income, Operating |  | $ 25.5 | $ 24.0 | $ 86.6 | $ 65.7
[1] | The net unrealized gain recognized in net investment income for the three and nine months ended September 30, 2025 related to private equity partnerships still held at September 30, 2025 was $28.8 million and $86.4 million, respectively, reduced by net management fees and partnership expenses of $(7.1) million and $(21.1) million, respectively. The net unrealized gain recognized in net investment income for the three and nine months ended September 30, 2024 related to private equity partnerships still held at September 30, 2024 was $25.3 million and $87.6 million, respectively, reduced by net management fees and partnership expenses of $(5.7) million and $(15.0) million, respectively. See Note 3 for further discussion of private equity partnerships.

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