Contractual Maturities of Debt Securities (Detail) (Truck and Other, USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Truck and Other
Amortized Cost Maturities:
Within one year	$ 326.6
One to five years	615.7
Six to ten years	0.2
More than ten years	1.3
AMORTIZED COST	943.8	900.7
Fair Value Maturities:
Within one year	328.3
One to five years	626.1
Six to ten years	0.2
More than ten years	1.3
FAIR VALUE	$ 955.9	$ 910.1