Investments - Available-for-Sale Debt Securities in Unrealized Loss Position (Details) - USD ($) $ in Millions |
Jun. 30, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Fair Value | ||
| Less than 12 months | $ 1,092.4 | $ 1,022.3 |
| 12 months or longer | 11.6 | 423.1 |
| Total | 1,104.0 | 1,445.4 |
| Gross Unrealized Losses | ||
| Less than 12 months | (0.8) | (3.5) |
| 12 months or longer | 0.0 | (0.5) |
| Total | (0.8) | (4.0) |
| U.S. government and agency securities | ||
| Fair Value | ||
| Less than 12 months | 1,050.5 | 947.3 |
| 12 months or longer | 8.6 | 341.1 |
| Total | 1,059.1 | 1,288.4 |
| Gross Unrealized Losses | ||
| Less than 12 months | (0.8) | (3.3) |
| 12 months or longer | 0.0 | (0.2) |
| Total | (0.8) | (3.5) |
| Corporate debt securities | ||
| Fair Value | ||
| Less than 12 months | 41.9 | 75.0 |
| 12 months or longer | 3.0 | 82.0 |
| Total | 44.9 | 157.0 |
| Gross Unrealized Losses | ||
| Less than 12 months | 0.0 | (0.2) |
| 12 months or longer | 0.0 | (0.3) |
| Total | $ 0.0 | $ (0.5) |
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- 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
|
| X | ||||||||||
- 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
|
| X | ||||||||||
- 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
|
| X | ||||||||||
- 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
|
| X | ||||||||||
- 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
|
| X | ||||||||||
- 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
|
| X | ||||||||||
- Definition Debt Securities, Available-For-Sale, Unrealized Loss Position, Fair Value No definition available.
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|