Summary of Cumulative Effect of the Changes Made for the Adoption of ASU 2016-02 (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	[1]
Truck, Parts and Other
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other noncurrent assets, net	$ 810.5	$ 692.8	$ 651.9
Accounts payable, accrued expenses and other	3,539.8	3,040.3	3,027.7
Other liabilities	1,372.0	1,174.2	1,145.7
Financial Services
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other assets	867.5	552.9	547.1
Accounts payable, accrued expenses and other	637.5	524.5	523.2
Deferred taxes and other liabilities	$ 753.7	709.2	$ 704.9
ASU 2016-02 | Truck, Parts and Other | Adjustments
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other noncurrent assets, net		40.9
Accounts payable, accrued expenses and other		12.6
Other liabilities		28.5
ASU 2016-02 | Financial Services | Adjustments
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other assets		5.8
Accounts payable, accrued expenses and other		1.3
Deferred taxes and other liabilities		$ 4.3

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