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Investments Investment Income (Detail) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2023 | Mar. 31, 2022
Net Investment Income |  |  |
Gross Investment Income, Operating |  | $ 526.5 | $ 539.8
Less Investment Expenses |  | 14.7 | 9.6
Less Investment Income on PFA Assets |  | 3.0 | 3.0
Net Investment Income |  | 508.8 | 527.2
Fixed Maturity Securities |  |  |
Net Investment Income |  |  |
Gross Investment Income, Operating |  | 455.1 | 455.5
Derivatives |  |  |
Net Investment Income |  |  |
Gross Investment Income, Operating |  | 11.9 | 14.4
Mortgage Loans |  |  |
Net Investment Income |  |  |
Gross Investment Income, Operating |  | 23.4 | 27.0
Policy Loans |  |  |
Net Investment Income |  |  |
Gross Investment Income, Operating |  | 5.0 | 4.7
Perpetual Preferred Securities |  |  |
Net Investment Income |  |  |
Gross Investment Income, Operating | [1] | 0.9 | 2.9
Private Equity Partnerships |  |  |
Net Investment Income |  |  |
Gross Investment Income, Operating | [2] | 14.3 | 32.4
Other Long-term Investments |  |  |
Net Investment Income |  |  |
Gross Investment Income, Operating |  | 1.8 | 2.1
Short-term Investments |  |  |
Net Investment Income |  |  |
Gross Investment Income, Operating |  | $ 14.1 | $ 0.8
[1] | The net unrealized gain (loss) recognized in net investment income for the three months ended March 31, 2023 related to perpetual preferred securities still held at March 31, 2023 was $0.7 million. The net unrealized gain (loss) recognized in net investment income for the three months ended March 31, 2022 related to perpetual preferred securities still held at March 31, 2022 was $2.4 million.
[2] | The net unrealized gain (loss) recognized in net investment income for the three months ended March 31, 2023 related to private equity partnerships still held at March 31, 2023 was $17.8 million, reduced by net management fees and partnership expenses of $(3.5) million. The net unrealized gain (loss) recognized in net investment income for the three months ended March 31, 2022 related to private equity partnerships still held at March 31, 2022 was $36.2 million, reduced by net management fees and partnership expense of $(3.8) million. See Note 3 for further discussion of private equity partnerships.

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