Contractual Maturities of Marketable Debt Securities (Detail) (Truck, Parts and Other, USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Truck, Parts and Other
Amortized Cost Maturities:
Within one year	$ 474.2
One to five years	839.0
More than ten years	0.1
Amortized Cost	1,313.3	1,264.9
Fair Value Maturities:
Within one year	474.8
One to five years	845.7
More than ten years	0.1
Fair Value	$ 1,320.6	$ 1,267.5	[1]

[1] The December 31, 2013 consolidated balance sheet has been derived from audited financial statements.