Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 25, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Registrant Name	PACCAR INC
Trading Symbol	PCAR
Entity Central Index Key	0000075362
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		345,873,618
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity File Number	001-14817
Entity Tax Identification Number	91-0351110
Entity Address, Address Line One	777 - 106th Ave. N.E.
Entity Address, City or Town	Bellevue
Entity Address, State or Province	WA
Entity Address, Postal Zip Code	98004
City Area Code	(425)
Local Phone Number	468-7400
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false
Title of Each Class	Common stock, $1 par value
Name of Each Exchange on Which Registered	NASDAQ