Marketable Debt Securities (Detail) (Truck, Parts and Other, USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,246.6	$ 1,264.9
Unrealized Gains	4.3	3.6
Unrealized Losses	0.5	1.0
Fair Value	1,250.4	1,267.5	[1]
U.S. tax-exempt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	218.0	214.9
Unrealized Gains	1.2	1.2
Unrealized Losses	0.1
Fair Value	219.1	216.1
U.S. corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	56.5	78.2
Unrealized Gains	0.1	0.1
Unrealized Losses		0.1
Fair Value	56.6	78.2
U.S. government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5.5	5.5
Fair Value	5.5	5.5
Non-U.S. corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	683.5	608.5
Unrealized Gains	2.0	1.2
Unrealized Losses	0.1	0.4
Fair Value	685.4	609.3
Non-U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	183.5	217.3
Unrealized Gains	0.9	0.7
Unrealized Losses	0.3	0.5
Fair Value	184.1	217.5
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99.6	140.5
Unrealized Gains	0.1	0.4
Fair Value	$ 99.7	$ 140.9

[1] The December 31, 2013 consolidated balance sheet has been derived from audited financial statements.