Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Notional maturities for all interest-rate contracts for the remainder of the fiscal year.

+ References

No definition available.

+ Details

Name:	pcar_NotionalAmountOfInterestRateDerivativesMaturingInReminderOfFiscalYear
Namespace Prefix:	pcar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notional maturities for all interest-rate contracts during fiscal year five.

+ References

No definition available.

+ Details

Name:	pcar_NotionalAmountOfInterestRateDerivativesMaturingInYearFive
Namespace Prefix:	pcar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notional maturities for all interest-rate contracts during fiscal year four.

+ References

No definition available.

+ Details

Name:	pcar_NotionalAmountOfInterestRateDerivativesMaturingInYearFour
Namespace Prefix:	pcar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notional maturities for all interest-rate contracts during fiscal year six.

+ References

No definition available.

+ Details

Name:	pcar_NotionalAmountOfInterestRateDerivativesMaturingInYearSix
Namespace Prefix:	pcar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notional maturities for all interest-rate contracts during fiscal year three.

+ References

No definition available.

+ Details

Name:	pcar_NotionalAmountOfInterestRateDerivativesMaturingInYearThree
Namespace Prefix:	pcar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notional maturities for all interest-rate contracts during the next fiscal year (year two).

+ References

No definition available.

+ Details

Name:	pcar_NotionalAmountOfInterestRateDerivativesMaturingInYearTwo
Namespace Prefix:	pcar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notional maturities for all interest-rate contracts maturing thereafter.

+ References

No definition available.

+ Details

Name:	pcar_NotionalAmountOfInterestRateDerivativesMaturingThereafter
Namespace Prefix:	pcar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

+ Details

Name:	us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective fair value hedge that is amortized upon discontinuation of the fair value hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 35
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=82917030&loc=d3e75592-113984

+ Details

Name:	us-gaap_DeferredGainLossOnDiscontinuationOfFairValueHedge
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

+ Details

Name:	us-gaap_DerivativeAssetNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Description of the relevant terms of the derivative. Includes the type of instrument, risk being hedged, notional amount, counterparty, inception date, maturity date, relevant interest rates, strike price, cap price, and floor price.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeDescriptionOfTerms
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=SL51823488-111719

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeInstrumentsGainLossReclassificationFromAccumulatedOCIToIncomeEstimatedNetAmountToBeTransferred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

+ Details

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

+ Details

Name:	us-gaap_MaximumLengthOfTimeHedgedInCashFlowHedge1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_FairValueHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=pcar_FinancialServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	$ 50.0		$ 57.8
Fair Value Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Remaining cumulative basis adjustments on discontinued hedge relationship	$ (2.4)
Cash Flow Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Maximum length of future cash flow hedges	9 years 10 months 24 days
Accumulated net gain on derivative contracts included in accumulated other comprehensive loss expected to be recognized in the Consolidated Statements of Comprehensive Income in the following 12 months, net of tax	$ 2.6
Designated under hedge accounting
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	49.1		57.1
Interest-Rate Contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of outstanding contracts	3,155.6
Notional maturities for interest-rate contracts 2018	906.7
Notional maturities for interest-rate contracts 2019	934.1
Notional maturities for interest-rate contracts 2020	450.2
Notional maturities for interest-rate contracts 2021	634.4
Notional maturities for interest-rate contracts 2022	141.8
Notional maturities for interest-rate contracts 2023	15.8
Notional maturities for interest-rate contracts thereafter	72.6
Reclassification from AOCI	9.3	$ 45.8
(Income) Expense recognized in earnings	0.0	0.0
Interest-Rate Contracts \| Financial Services \| Designated under hedge accounting \| Other Assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	45.7		$ 53.3
Foreign-exchange contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative notional amount outstanding	$ 523.7
Foreign-exchange contracts maturity period	within one year
Reclassification from AOCI	$ 2.5	4.3
(Income) Expense recognized in earnings	(6.3)	(70.1)
Foreign-exchange contracts \| Financial Services \| Cash Flow Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Reclassification from AOCI	$ 0.0	$ 0.0