Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other $ in Millions	Mar. 31, 2024 USD ($)
Amortized Cost Maturities:
Within one year	$ 490.1
One to five years	1,347.6
Six to ten years	0.4
More than ten years	11.5
Marketable debt securities, Cost	1,849.6
Fair Value Maturities:
Within one year	484.9
One to five years	1,332.9
Six to ten years	0.4
More than ten years	10.4
Fair Value	$ 1,828.6

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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