Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other $ in Millions	Sep. 30, 2021 USD ($)
Amortized Cost Maturities:
Within one year	$ 432.9
One to five years	1,083.7
Six to ten years	10.8
More than ten years	11.7
Marketable debt securities, Cost	1,539.1
Fair Value Maturities:
Within one year	434.7
One to five years	1,089.1
Six to ten years	10.8
More than ten years	11.6
Fair Value	$ 1,546.2

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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