Significant Accounting Policies - Additional Information (Detail) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) Segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jan. 01, 2017 USD ($)
Accounting Policies [Abstract]
Reportable segments | Segment									3
Liquid investments maturity period									90 days
Goodwill	$ 103.0				$ 105.6				$ 103.0	$ 105.6
Goodwill, impairment charges									0.0	0.0	$ 0.0
Derivative assets	118.4				137.3				118.4	137.3
Subsequent Event | Accounting Standards Update 2016-16
Accounting Policies [Abstract]
New accounting pronouncement, cumulative effect of change on prepaid income taxes and retained earnings												$ (20.0)
Trade Receivables
Accounting Policies [Abstract]
Trade and other receivables, net	734.6				739.2				734.6	739.2
Other Receivables
Accounting Policies [Abstract]
Trade and other receivables, net	127.6				139.8				$ 127.6	139.8
Engines manufactured by PACCAR
Accounting Policies [Abstract]
Warranty period									2 years
Designated under hedge accounting
Accounting Policies [Abstract]
Derivative assets	113.6				136.1				$ 113.6	136.1
Minimum
Accounting Policies [Abstract]
Lease and guarantee periods (in years)									3 years
Estimated useful life of equipment (in years)									4 years
Warranty period									1 year
Maximum
Accounting Policies [Abstract]
Lease and guarantee periods (in years)									5 years
Estimated useful life of equipment (in years)									9 years
Warranty period									5 years
Truck, Parts and Other
Accounting Policies [Abstract]
Trade and other receivables, net	862.2				879.0				$ 862.2	$ 879.0
Trade receivable days outstanding considered past due									30 days	30 days	30 days
Allowance for credit losses for Truck, Parts and Other	1.7				1.3				$ 1.7	$ 1.3
Net charge-offs									0.1	0.3	$ 0.2
Financial Services
Accounting Policies [Abstract]
Lease rental revenue									760.5	728.5	741.6
Depreciation and other expenses	165.3	$ 162.6	$ 156.4	$ 150.9	144.9	$ 152.5	$ 145.9	$ 140.4	$ 635.2	$ 583.7	588.5
Months contractual terms extended									4 months	7 months
Financial Services | Designated under hedge accounting | Interest-Rate Contracts | Other Assets
Accounting Policies [Abstract]
Derivative assets	$ 109.7				$ 132.2				$ 109.7	$ 132.2
Financial Services | Minimum | Loans And Leases
Accounting Policies [Abstract]
Receivable, collection period									36 months
Financial Services | Minimum | Loans Receivable
Accounting Policies [Abstract]
Origination cost, amortization period									36 months
Financial Services | Maximum | Loans And Leases
Accounting Policies [Abstract]
Receivable, collection period									60 months
Financial Services | Maximum | Loans Receivable
Accounting Policies [Abstract]
Origination cost, amortization period									60 months
Financial Services | Operating Lease
Accounting Policies [Abstract]
Lease rental revenue									$ 698.9	668.6	681.5
Depreciation and other expenses									$ 581.7	$ 536.2	$ 544.0