Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Amortized Cost Maturities:
Within one year	$ 404.4
One to five years	800.9
More than ten years	9.1
Amortized Cost	1,214.4	$ 1,141.9
Fair Value Maturities:
Within one year	404.6
One to five years	802.3
More than ten years	9.1
Fair Value	$ 1,216.0	$ 1,140.9	[1]

[1] The December 31, 2016 consolidated balance sheet has been derived from audited financial statements.