Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Amortized Cost Maturities:
Within one year	$ 308.2
One to five years	886.6
Six to ten years	0.1
More than ten years	9.1
Amortized Cost	1,204.0	$ 1,141.9
Fair Value Maturities:
Within one year	308.4
One to five years	888.8
Six to ten years	0.1
More than ten years	9.1
Fair Value	$ 1,206.4	$ 1,140.9	[1]

[1] The December 31, 2016 consolidated balance sheet has been derived from audited financial statements.