Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost Maturities:
Within one year	$ 313.9
One to five years	1,088.6
Six to ten years	5.2
More than ten years	2.0
Amortized Cost	1,409.7	$ 1,154.0
Fair Value Maturities:
Within one year	315.7
One to five years	1,106.1
Six to ten years	5.2
More than ten years	2.0
Fair Value	$ 1,429.0	$ 1,162.1

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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