Contractual Maturities of Marketable Debt Securities (Detail) (Truck, Parts and Other, USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Truck, Parts and Other
Amortized Cost Maturities:
Within one year	$ 530.0
One to five years	667.1
Six to ten years	0.1
More than ten years	0.4
Amortized Cost	1,197.6	1,183.5
Fair Value Maturities:
Within one year	531.1
One to five years	669.5
Six to ten years	0.1
More than ten years	0.4
Fair Value	$ 1,201.1	$ 1,192.7	[1]

[1] The December 31, 2012 consolidated balance sheet has been derived from audited financial statements.