Fair Value Measurements - Reconciliation for Assets and Liabilities Measured at Fair Value on a Recurring basis (Details) - Recurring Fair Value Measurements - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, net derivative assets (liabilities) | $ 23.3 | $ (13.1) | $ 17.9 | $ 13.5 |
| Total realized/unrealized gains (losses) included in net income, net derivative assets (liabilities) | $ (19.5) | $ 18.3 | $ (15.3) | $ (9.5) |
| Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative |
| Net purchases, sales, issuances and settlements, net derivative assets (liabilities) | $ 1.4 | $ (0.3) | $ 2.6 | $ 0.9 |
| Ending balance, net derivative assets (liabilities) | 5.2 | 4.9 | 5.2 | 4.9 |
| Investment and universal life contracts | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, liabilities | (2,142.5) | (863.7) | (1,410.2) | (578.4) |
| Total realized/unrealized gains (losses) included in net income, liabilities | $ (156.6) | $ (222.2) | $ (679.5) | $ (221.2) |
| Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative |
| Net purchases, sales, issuances and settlements, liabilities | $ (133.5) | $ (142.9) | $ (342.9) | $ (429.2) |
| Ending balance, liabilities | (2,432.6) | (1,228.8) | (2,432.6) | (1,228.8) |
| Funds withheld payable embedded derivative | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, liabilities | 2,706.4 | 2,825.2 | 2,633.4 | 3,014.5 |
| Total realized/unrealized gains (losses) included in net income, liabilities | $ 818.2 | $ (266.0) | $ 891.2 | $ (455.3) |
| Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative |
| Ending balance, liabilities | $ 3,524.6 | $ 2,559.2 | $ 3,524.6 | $ 2,559.2 |
| Fixed maturities | Available-for-sale | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, assets | 4,050.8 | 4,327.8 | 4,304.2 | 3,898.2 |
| Total realized/unrealized gains (losses) included in net income, assets | $ (16.5) | $ (21.5) | $ (50.6) | $ (5.5) |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative |
| Total realized/unrealized gains (losses) included in other comprehensive income, assets | $ (61.9) | $ 7.2 | $ (55.8) | $ 11.6 |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax |
| Net purchases, sales, issuances and settlements, assets | $ 95.0 | $ (2.0) | $ (97.9) | $ 310.5 |
| Transfers into Level 3, assets | 78.2 | 163.4 | 121.5 | |
| Transfers out of Level 3, assets | (31.9) | (94.2) | (149.6) | (119.0) |
| Ending balance, assets | 4,113.7 | 4,217.3 | 4,113.7 | 4,217.3 |
| States and political subdivisions | Available-for-sale | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, assets | 99.8 | 67.8 | 68.4 | 66.8 |
| Total realized/unrealized gains (losses) included in other comprehensive income, assets | $ (3.9) | $ 0.9 | $ (4.1) | $ 2.8 |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax |
| Net purchases, sales, issuances and settlements, assets | $ (0.4) | $ (0.5) | $ (1.4) | $ (1.4) |
| Transfers into Level 3, assets | 32.6 | |||
| Transfers out of Level 3, assets | (31.9) | (31.9) | ||
| Ending balance, assets | 63.6 | 68.2 | 63.6 | 68.2 |
| Corporate debt securities | Available-for-sale | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, assets | 2,516.8 | 2,444.0 | 2,477.7 | 2,350.4 |
| Total realized/unrealized gains (losses) included in net income, assets | $ (14.8) | $ (21.5) | $ (46.8) | $ (5.6) |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative |
| Total realized/unrealized gains (losses) included in other comprehensive income, assets | $ (52.3) | $ 3.8 | $ (46.0) | $ (4.1) |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax |
| Net purchases, sales, issuances and settlements, assets | $ 46.3 | $ (10.9) | $ 111.1 | $ 74.7 |
| Transfers into Level 3, assets | 76.0 | 76.0 | ||
| Ending balance, assets | 2,572.0 | 2,415.4 | 2,572.0 | 2,415.4 |
| Commercial mortgage-backed securities | Available-for-sale | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, assets | 2.2 | 2.6 | 2.4 | 2.7 |
| Total realized/unrealized gains (losses) included in net income, assets | (1.7) | (1.7) | ||
| Total realized/unrealized gains (losses) included in other comprehensive income, assets | 0.1 | |||
| Net purchases, sales, issuances and settlements, assets | (0.1) | (0.1) | (0.3) | (0.3) |
| Transfers into Level 3, assets | 2.2 | 2.2 | ||
| Ending balance, assets | 2.6 | 2.5 | 2.6 | 2.5 |
| Other debt obligations | Available-for-sale | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, assets | 1,432.0 | 1,813.4 | 1,755.7 | 1,478.3 |
| Total realized/unrealized gains (losses) included in net income, assets | $ (2.1) | $ 0.1 | ||
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | ||
| Total realized/unrealized gains (losses) included in other comprehensive income, assets | $ (5.7) | $ 2.5 | $ (5.7) | $ 12.8 |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | Other Comprehensive Income Available for Sale Securities Period Increase Decrease Net of Tax, Other Comprehensive Income Derivatives Period Increase (Decrease), Net of Tax | |
| Net purchases, sales, issuances and settlements, assets | $ 49.2 | $ 9.5 | (207.3) | $ 237.5 |
| Transfers into Level 3, assets | 52.6 | 121.5 | ||
| Transfers out of Level 3, assets | (94.2) | (117.7) | (119.0) | |
| Ending balance, assets | 1,475.5 | 1,731.2 | 1,475.5 | 1,731.2 |
| Fixed maturities, trading | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, assets | 404.5 | 491.9 | 457.4 | 562.6 |
| Total realized/unrealized gains (losses) included in net income, assets | $ (6.5) | $ (3.4) | $ (18.5) | $ (15.3) |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative |
| Net purchases, sales, issuances and settlements, assets | $ 47.2 | $ 11.9 | $ 6.3 | $ (42.1) |
| Transfers out of Level 3, assets | (4.8) | |||
| Ending balance, assets | 445.2 | 500.4 | 445.2 | 500.4 |
| Mortgage loans | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, assets | 140.6 | |||
| Net purchases, sales, issuances and settlements, assets | (140.6) | |||
| Other investments | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, assets | 88.2 | 119.3 | 167.2 | 131.2 |
| Total realized/unrealized gains (losses) included in net income, assets | $ (3.5) | $ (2.5) | $ (10.6) | $ (2.7) |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative |
| Net purchases, sales, issuances and settlements, assets | $ (22.4) | $ 19.7 | $ (94.3) | $ 8.0 |
| Ending balance, assets | 62.3 | 136.5 | 62.3 | 136.5 |
| Separate account assets | ||||
| Changes in Level 3 fair value measurements rollforward, assets and liabilities | ||||
| Beginning balance, assets | 760.4 | 741.4 | 742.5 | 726.7 |
| Total realized/unrealized gains (losses) included in net income, assets | $ 3.7 | $ 2.0 | $ 21.6 | $ 16.7 |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative | Gain (Loss) on Investments, Change In Fair Value Of Funds Withheld Embedded Derivative |
| Net purchases, sales, issuances and settlements, assets | $ 1.5 | $ 1.5 | ||
| Ending balance, assets | $ 765.6 | $ 743.4 | $ 765.6 | $ 743.4 |