Investments - Net Unrealized Gains and Losses on Available-for-Sale Securities and Derivative Instruments (Details) - USD ($) $ in Millions |
Jun. 30, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Net Unrealized Gains and Losses on Available-for-Sale Securities and Derivative Instruments | ||
| Net unrealized gains (losses) on fixed maturities, available-for-sale | $ (4,900.5) | $ (5,942.5) |
| Net unrealized gains (losses) on derivative instruments | (124.6) | 66.1 |
| Adjustments for assumed changes in amortization patterns | 4.7 | 5.1 |
| Adjustments for assumed changes in policyholder liabilities | 27.9 | 12.2 |
| Net unrealized gains (losses) on other investments and noncontrolling interest adjustments | (47.2) | (52.5) |
| Provision for deferred income tax benefits (taxes) | 1,086.3 | 1,270.5 |
| Net unrealized gains (losses) on available-for-sale securities and derivative instruments | $ (3,953.4) | $ (4,641.1) |