Investments - Available-for-Sale Debt Securities in Unrealized Loss Position (Details) - USD ($) $ in Millions |
Mar. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Fair Value | ||
| Less than 12 months | $ 757.5 | $ 1,022.3 |
| 12 months or longer | 168.5 | 423.1 |
| Total | 926.0 | 1,445.4 |
| Gross Unrealized Losses | ||
| Less than 12 months | (1.1) | (3.5) |
| 12 months or longer | (0.1) | (0.5) |
| Total | (1.2) | (4.0) |
| U.S. government and agency securities | ||
| Fair Value | ||
| Less than 12 months | 708.6 | 947.3 |
| 12 months or longer | 146.5 | 341.1 |
| Total | 855.1 | 1,288.4 |
| Gross Unrealized Losses | ||
| Less than 12 months | (1.0) | (3.3) |
| 12 months or longer | (0.1) | (0.2) |
| Total | (1.1) | (3.5) |
| Corporate debt securities | ||
| Fair Value | ||
| Less than 12 months | 48.9 | 75.0 |
| 12 months or longer | 22.0 | 82.0 |
| Total | 70.9 | 157.0 |
| Gross Unrealized Losses | ||
| Less than 12 months | (0.1) | (0.2) |
| 12 months or longer | 0.0 | (0.3) |
| Total | $ (0.1) | $ (0.5) |
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- References No definition available.
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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- Definition Debt Securities, Available-For-Sale, Unrealized Loss Position, Fair Value No definition available.
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