Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Amortized Cost Maturities:
Within one year	$ 319.1
One to five years	740.7
Six to ten years	3.7
More than ten years	15.0
Amortized Cost	1,078.5	$ 1,023.5
Fair Value Maturities:
Within one year	318.8
One to five years	744.1
Six to ten years	3.7
More than ten years	15.0
Fair Value	$ 1,081.6	$ 1,020.4	[1]

[1] The December 31, 2018 consolidated balance sheet has been derived from audited financial statements.