Long-Duration Insurance Contracts - Policyholder Account Balances (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
Dec. 31, 2025 |
|
| Policyholder Account Balance [Roll Forward] | |||||
| Beginning balance | $ 5,064.1 | ||||
| Interest credited | $ 55.6 | $ 55.7 | 164.0 | $ 161.2 | |
| Ending balance | 5,043.2 | 5,043.2 | $ 5,064.1 | ||
| Indexed Universal Life | |||||
| Policyholder Account Balance [Roll Forward] | |||||
| Beginning balance | 108.0 | 82.3 | 95.5 | 72.9 | 72.9 |
| Premiums received | 7.9 | 5.8 | 22.0 | 16.7 | |
| Surrenders and withdrawals | (0.6) | (0.7) | (2.0) | (1.5) | |
| Benefit payments | 0.0 | 0.0 | (0.4) | 0.0 | |
| Net transfers from (to) separate account | (1.0) | (0.1) | (1.1) | (0.3) | |
| Interest credited | 1.7 | 1.2 | 4.6 | 3.0 | |
| Other | (0.8) | (1.3) | (3.2) | (3.6) | |
| Ending balance | $ 115.3 | $ 87.2 | $ 115.3 | $ 87.2 | 95.5 |
| Weighted-average crediting rate | 6.40% | 5.80% | 6.00% | 5.10% | |
| Net amount at risk | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | |
| Cash surrender value | 90.7 | 66.6 | 90.7 | 66.6 | |
| Experience life | |||||
| Policyholder Account Balance [Roll Forward] | |||||
| Beginning balance | 52.8 | 56.5 | 54.8 | 58.0 | 58.0 |
| Premiums received | (0.2) | (0.2) | (0.6) | (0.6) | |
| Surrenders and withdrawals | (0.8) | (0.9) | (2.8) | (2.7) | |
| Benefit payments | (0.4) | (0.3) | (1.2) | (1.0) | |
| Net transfers from (to) separate account | 0.0 | 0.0 | 0.0 | 0.0 | |
| Interest credited | 0.6 | 0.7 | 1.9 | 2.1 | |
| Other | 0.0 | (0.1) | (0.1) | (0.1) | |
| Ending balance | $ 52.1 | $ 55.7 | $ 52.1 | $ 55.7 | 54.8 |
| Weighted-average crediting rate | 5.00% | 5.10% | 4.90% | 5.00% | |
| Net amount at risk | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | |
| Cash surrender value | 51.5 | 55.1 | 51.5 | 55.1 | |
| Fixed Account Annuities | |||||
| Policyholder Account Balance [Roll Forward] | |||||
| Beginning balance | 4,469.0 | 4,495.1 | 4,486.8 | 4,508.4 | 4,508.4 |
| Premiums received | 55.1 | 61.3 | 131.3 | 151.3 | |
| Surrenders and withdrawals | (80.3) | (77.0) | (242.6) | (247.0) | |
| Benefit payments | (16.8) | (14.9) | (49.0) | (58.1) | |
| Net transfers from (to) separate account | 6.8 | 3.6 | 20.9 | 23.8 | |
| Interest credited | 42.9 | 42.6 | 127.1 | 126.2 | |
| Other | (4.3) | 3.9 | (2.2) | 10.0 | |
| Ending balance | $ 4,472.3 | $ 4,514.6 | $ 4,472.3 | $ 4,514.6 | 4,486.8 |
| Weighted-average crediting rate | 3.90% | 3.90% | 3.90% | 3.80% | |
| Net amount at risk | $ 20.9 | $ 23.9 | $ 20.9 | $ 23.9 | |
| Cash surrender value | 4,411.0 | 4,470.7 | 4,411.0 | 4,470.7 | |
| Fixed Indexed Account Annuities | |||||
| Policyholder Account Balance [Roll Forward] | |||||
| Beginning balance | 360.7 | 388.6 | 373.3 | 409.5 | 409.5 |
| Premiums received | 2.6 | 3.1 | 8.3 | 10.7 | |
| Surrenders and withdrawals | (10.3) | (9.3) | (30.3) | (33.7) | |
| Benefit payments | (1.8) | (0.6) | (3.2) | (3.0) | |
| Net transfers from (to) separate account | (0.3) | (0.2) | (0.6) | (0.8) | |
| Interest credited | 4.8 | 4.0 | 11.9 | 10.2 | |
| Other | (0.9) | (3.3) | (4.5) | (10.6) | |
| Ending balance | $ 354.8 | $ 382.3 | $ 354.8 | $ 382.3 | 373.3 |
| Weighted-average crediting rate | 5.50% | 4.20% | 4.50% | 3.50% | |
| Net amount at risk | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | |
| Cash surrender value | 350.7 | 377.2 | 350.7 | 377.2 | |
| SPIA (non-life contingent) | |||||
| Policyholder Account Balance [Roll Forward] | |||||
| Beginning balance | 25.8 | 27.9 | 26.1 | 28.6 | 28.6 |
| Premiums received | 0.5 | 0.3 | 2.4 | 1.7 | |
| Surrenders and withdrawals | 0.0 | (0.1) | (0.4) | (0.3) | |
| Benefit payments | (1.1) | (0.9) | (3.3) | (3.2) | |
| Net transfers from (to) separate account | 0.0 | 0.0 | 0.0 | 0.0 | |
| Interest credited | 0.2 | 0.2 | 0.6 | 0.7 | |
| Other | 0.0 | 0.0 | 0.0 | (0.1) | |
| Ending balance | $ 25.4 | $ 27.4 | $ 25.4 | $ 27.4 | $ 26.1 |
| Weighted-average crediting rate | 3.30% | 2.90% | 3.30% | 3.60% | |
| Net amount at risk | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | |
| Cash surrender value | $ 25.1 | $ 27.0 | $ 25.1 | $ 27.0 | |