Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost Maturities:
Within one year	$ 316.5
One to five years	851.9
Six to ten years	5.2
More than ten years	0.2
Amortized Cost	1,173.8	$ 1,154.0	[1]
Fair Value Maturities:
Within one year	319.1
One to five years	869.8
Six to ten years	5.2
More than ten years	0.2
Fair Value	$ 1,194.3	$ 1,162.1

[1] The December 31, 2019 consolidated balance sheet has been derived from audited financial statements.