Contractual Maturities on Marketable Debt Securities (Detail) - Truck, Parts and Other $ in Millions	Mar. 31, 2025 USD ($)
Amortized Cost Maturities:
Within one year	$ 525.9
One to five years	2,275.0
Six to ten years	1.0
More than ten years	5.0
Marketable debt securities, Cost	2,806.9
Fair Value Maturities:
Within one year	526.0
One to five years	2,288.3
Six to ten years	1.0
More than ten years	4.5
Fair Value	$ 2,819.8

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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