Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost Maturities:
Within one year	$ 291.6
One to five years	806.4
Six to ten years	24.0
More than ten years	32.0
Amortized Cost	1,154.0	$ 1,023.5
Fair Value Maturities:
Within one year	292.1
One to five years	813.9
Six to ten years	24.1
More than ten years	32.0
Fair Value	$ 1,162.1	$ 1,020.4

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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