Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions |
Total |
Reclassification out of Accumulated Other Comprehensive Loss [Member] |
Preferred Stock [Member] |
Common Stock [Member] |
Additional Paid-in Capital [Member] |
Net Unrealized Appreciation (Depreciation) on Investments [Member] |
Net Unrealized Appreciation (Depreciation) on Investments [Member]
Reclassification out of Accumulated Other Comprehensive Loss [Member]
|
Defined Benefit Pension and Postretirement Plans [Member] |
Defined Benefit Pension and Postretirement Plans [Member]
Reclassification out of Accumulated Other Comprehensive Loss [Member]
|
Long Duration Insurance Contracts [Member] |
Retained Earnings [Member] |
Retained Earnings [Member]
Adjustment [Member]
|
Retained Earnings [Member]
Adjusted Balance [Member]
|
Accumulated Other Comprehensive Income (Loss), Net of Tax [Member] |
Treasury Stock [Member] |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Balance at beginning of period at Dec. 31, 2024 | $ 0.0 | $ 0.6 | $ 1,973.6 | $ (403.5) | $ (55.2) | $ 2.4 | $ 3,209.6 | $ 1.9 | $ 3,211.5 | $ (1,885.7) | |||||
| Net income | $ 128.2 | $ (15.8) | $ (14.6) | 128.2 | |||||||||||
| Shares purchased at cost | (11.0) | ||||||||||||||
| Employee and director stock-based awards and other | 4.7 | ||||||||||||||
| Net appreciation (depreciation) on available-for-sale securities | 111.2 | 111.2 | |||||||||||||
| Net amount recognized as net periodic benefit cost | $ 1.4 | ||||||||||||||
| Net change in market risk | (1.0) | (1.0) | |||||||||||||
| Dividends to shareholders | (32.9) | ||||||||||||||
| Net shares reissued at cost under employee stock-based compensation plans and other | 0.1 | ||||||||||||||
| Balance at end of period at Mar. 31, 2025 | 3,044.4 | 1,978.3 | (292.3) | (53.8) | 1.4 | 3,306.8 | $ (344.7) | (1,896.6) | |||||||
| Balance at beginning of period at Dec. 31, 2025 | 3,571.5 | $ 0.0 | $ 0.6 | 2,013.5 | (116.3) | (54.3) | (0.8) | 3,741.6 | $ 0.0 | $ 3,741.6 | (2,012.8) | ||||
| Net income | 186.8 | $ (6.1) | $ (4.9) | 186.8 | |||||||||||
| Shares purchased at cost | (87.5) | ||||||||||||||
| Employee and director stock-based awards and other | 2.5 | ||||||||||||||
| Net appreciation (depreciation) on available-for-sale securities | (68.9) | (68.9) | |||||||||||||
| Net amount recognized as net periodic benefit cost | $ 1.4 | ||||||||||||||
| Net change in market risk | 1.0 | 1.0 | |||||||||||||
| Dividends to shareholders | (33.9) | ||||||||||||||
| Net shares reissued at cost under employee stock-based compensation plans and other | (2.5) | ||||||||||||||
| Balance at end of period at Mar. 31, 2026 | $ 3,570.4 | $ 2,016.0 | $ (185.2) | $ (52.9) | $ 0.2 | $ 3,894.5 | $ (237.9) | $ (2,102.8) |
| X | ||||||||||
- Definition Amount of increase to additional paid-in capital (APIC) for recognition of cost for award under share-based payment arrangement. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of paid and unpaid cash dividends declared for classes of stock, for example, but not limited to, common and preferred. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount after tax of income (loss) from continuing operations attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- Definition Amount, after tax and reclassification adjustment, of unrealized gain (loss) from (increase) decrease in liability for future policy benefit from change in discount rate. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount, after tax and adjustment, of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and unrealized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity) from transfer to available-for-sale. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Value, after forfeiture, of shares issued under share-based payment arrangement. Excludes employee stock ownership plan (ESOP). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of equity (deficit) attributable to parent. Excludes temporary equity and equity attributable to noncontrolling interest. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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