Contractual Maturities of Marketable Debt Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost Maturities:
Within one year	$ 273.5
One to five years	769.2
Six to ten years	20.0
More than ten years	36.6
Amortized Cost	1,099.3	$ 1,023.5
Fair Value Maturities:
Within one year	273.8
One to five years	777.4
Six to ten years	20.0
More than ten years	36.6
Fair Value	$ 1,107.8	$ 1,020.4	[1]

[1] The December 31, 2018 consolidated balance sheet has been derived from audited financial statements.