Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Amortized Cost Maturities:
Within one year	$ 394.0
One to five years	1,000.0
Six to ten years	0.1
Amortized Cost	1,394.1	$ 1,264.8
Fair Value Maturities:
Within one year	394.6
One to five years	1,004.1
Six to ten years	0.1
Fair Value	$ 1,398.8	$ 1,272.0	[1]

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