Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Amortized Cost Maturities:
Within one year	$ 333.7
One to five years	694.1
More than ten years	24.4
Amortized Cost	1,052.2	$ 1,370.2
Fair Value Maturities:
Within one year	333.2
One to five years	688.9
More than ten years	24.4
Fair Value	$ 1,046.5	$ 1,367.1	[1]

[1] The December 31, 2017 consolidated balance sheet has been derived from audited financial statements.