Borrowings and Credit Arrangements - Additional Information (Detail) In Millions, unless otherwise specified	12 Months Ended				12 Months Ended			12 Months Ended		1 Months Ended	12 Months Ended												1 Months Ended	12 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2014 Syndicated revolving loan facility USD ($)	Dec. 31, 2014 PACCAR Mexico Medium-term Notes MXN	Apr. 30, 2011 PACCAR Mexico Medium-term Notes MXN	Apr. 30, 2011 PACCAR Mexico Commercial Papers MXN	Dec. 31, 2014 Parent Company Medium-term Notes	Feb. 28, 2014 Parent Company Medium-term Notes USD ($)	Feb. 28, 2014 Parent Company Medium-term Notes Manufacturing Debt USD ($)	Dec. 31, 2014 PACCAR Financial Corp. (PFC) Medium-term Notes USD ($)	Dec. 31, 2014 PACCAR's European finance subsidiary Medium-term Notes EUR (€)	Dec. 31, 2014 Truck, Parts and Other USD ($)	Dec. 31, 2013 Truck, Parts and Other USD ($)	Dec. 31, 2012 Truck, Parts and Other USD ($)	Dec. 31, 2013 Truck, Parts and Other Notes 6.90 Percent Due 2014 USD ($)	Dec. 31, 2014 Financial Services USD ($)	Dec. 31, 2013 Financial Services USD ($)	Dec. 31, 2014 Financial Services Medium-term Notes	Dec. 31, 2013 Financial Services Medium-term Notes	Dec. 31, 2014 Financial Services Commercial Papers	Dec. 31, 2013 Financial Services Commercial Papers	Apr. 30, 2011 Maximum PACCAR Mexico Commercial Papers	Dec. 31, 2014 Matures in June 2015 Syndicated revolving loan facility USD ($)	Dec. 31, 2014 Matures in June 2018 Syndicated revolving loan facility USD ($)	Dec. 31, 2014 Matures in June 2019 Syndicated revolving loan facility USD ($)
Debt Disclosure [Line Items]
Notes payable, Non-current																$ 150.0
Interest rate																6.90%	1.30%	1.70%	5.00%	5.00%	0.80%	1.20%
Maturity month and year																2014-02
Commercial paper and term notes																	8,094.7	8,032.1
Fair value hedges and unamortized discounts, net																	(1.0)	1.5
Interest paid on borrowings	136.3	149.3	149.9
Capitalized interest													1.3	10.3	10.3
Debt outstanding									500.0		4,150.0
Repayment of debt										150.0
Registration expiration					Expires in 2016			Fourth quarter of 2014			November 2015
Debt, unused borrowing capacity					8,000.0							366.9
Debt, borrowing capacity						10,000.0						1,500.0
Debt, renewal period												Second quarter of 2014
Commercial paper expiration period																							1 year
Maximum limit of borrowing capacity							5,000.0
Line of credit, maximum capacity	3,503.9			3,000.0																				1,000.0	1,000.0	1,000.0
Line of credit, unused borrowing capacity	$ 3,368.0
Line of credit, maturity date																								2015-06	2018-06	2019-06