Contractual Maturities of Marketable Debt Securities (Detail) (Truck, Parts and Other, USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Truck, Parts and Other
Amortized Cost Maturities:
Within one year	$ 534.7
One to five years	729.9
Six to ten years	0.3
Amortized Cost	1,264.9	1,183.5
Fair Value Maturities:
Within one year	535.5
One to five years	731.6
Six to ten years	0.4
Fair Value	$ 1,267.5	$ 1,192.7