Marketable Securities Held in Trusts - Continuous Loss Position (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 436.6	$ 337.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4.0	0.7
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	61.2	88.5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(3.4)	(3.9)
Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	74.1	17.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.9	0.2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	35.8	48.3
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2.5)	(2.7)
Municipal bonds
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	49.5	14.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.8	0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	25.4	40.2
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(0.9)	(1.2)
U.S. government bonds
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	313.0	306.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 2.3	$ 0.5

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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.

+ References

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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.

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