Marketable Securities Held in Trusts - Maturity Dates and Realized Gain and Loss (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
Dec. 31, 2025 |
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| Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity | |||||
| Debt Securities, Available-for-sale | $ 721.0 | $ 721.0 | $ 743.3 | ||
| Debt securities | |||||
| Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity | |||||
| Available-for-sale debt maturities due within one year, fair value | 18.7 | 18.7 | |||
| Available-for-sale debt maturities, after 1 but within 5 years, fair value | 225.6 | 225.6 | |||
| Available-for-sale debt maturities, after 5 but within 10 years, fair value | 413.9 | 413.9 | |||
| Available-for-sale debt maturities, after 10 years, fair value | 57.4 | 57.4 | |||
| Debt Securities, Available-for-sale | 715.6 | 715.6 | |||
| Debt Securities, Available-for-sale, Realized Gain | 0.1 | $ 0.6 | 0.8 | $ 1.3 | |
| Debt Securities, Available-for-sale, Realized Loss | $ 11.7 | $ 0.8 | $ 15.4 | $ 8.6 | |
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- Definition Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- References No definition available.
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- Definition Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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). Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Details
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