Contractual Maturities of Marketable Debt Securities (Detail) (Truck, Parts and Other, USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Truck, Parts and Other
Amortized Cost Maturities:
Within one year	$ 337.9
One to five years	881.8
Amortized Cost	1,219.7	1,264.8
Fair Value Maturities:
Within one year	338.5
One to five years	888.7
Fair Value	$ 1,227.2	$ 1,272.0	[1]

[1] The December 31, 2014 consolidated balance sheet has been derived from audited financial statements.