Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	[1]
Amortized Cost Maturities:
Within one year	$ 342.2
One to five years	1,056.6
Six to ten years	5.6
More than ten years	4.0
Amortized Cost	1,408.4	$ 1,409.7
Fair Value Maturities:
Within one year	343.9
One to five years	1,067.6
Six to ten years	5.6
More than ten years	4.0
Fair Value	$ 1,421.1	$ 1,429.0

[1] The December 31, 2020 consolidated balance sheet has been derived from audited financial statements.