Product Support Liabilities - Additional Information (Detail) $ in Millions	Dec. 31, 2020 USD ($)
Product Warranties Disclosures [Abstract]
Deferred revenues on extended warranties and R&M recognize, in 2021	$ 272.3
Deferred revenues on extended warranties and R&M recognize, in 2022	251.8
Deferred revenues on extended warranties and R&M recognize, in 2023	162.3
Deferred revenues on extended warranties and R&M recognize, in 2024	74.6
Deferred revenues on extended warranties and R&M recognize, in 2025	25.4
Deferred revenues on extended warranties and R&M recognize, thereafter	$ 9.4

Deferred revenue extended warranties and repair and maintenance recognize thereafter.

No definition available.

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

Deferred revenue extended warranties and repair and maintenance recognize year five.

No definition available.

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

Deferred revenue extended warranties and repair and maintenance recognize year four.

No definition available.

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

Deferred revenue extended warranties and repair and maintenance recognize year one.

No definition available.

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

Deferred revenue extended warranties and repair and maintenance recognize year three.

No definition available.

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

Deferred revenue extended warranties and repair and maintenance recognize year two.

No definition available.

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

No definition available.

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