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Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

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Borrowings and Credit Arrangements - Additional Information (Detail) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2016 MXN ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Feb. 19, 2021 USD ($)	Dec. 31, 2020 EUR (€)	Dec. 31, 2020 MXN ($)
Debt Disclosure [Line Items]
Interest paid on borrowings		$ 164.5	$ 203.8	$ 166.5
Line of credit, maximum capacity		3,523.1
Line of credit, unused borrowing capacity		3,292.2
Syndicated loan facility
Debt Disclosure [Line Items]
Line of credit, maximum capacity		3,000.0
Line of credit, outstanding amount		0.0
Expires in June 2019 \| Syndicated loan facility
Debt Disclosure [Line Items]
Line of credit, maximum capacity		$ 1,000.0
Line of credit, expiry date		2021-06
Expires in June 2022 \| Syndicated loan facility
Debt Disclosure [Line Items]
Line of credit, maximum capacity		$ 1,000.0
Line of credit, expiry date		2023-06
Expires in June 2023 \| Syndicated loan facility
Debt Disclosure [Line Items]
Line of credit, maximum capacity		$ 1,000.0
Line of credit, expiry date		2024-06
PACCAR's U.S. finance subsidiary \| Medium-term Notes
Debt Disclosure [Line Items]
Debt outstanding		$ 6,000.0
Registration expiration		2021-11
PACCAR's U.S. finance subsidiary \| Subsequent Event \| Medium-term Notes
Debt Disclosure [Line Items]
Debt outstanding					$ 400.0
PACCAR's European finance subsidiary \| Medium-term Notes
Debt Disclosure [Line Items]
Debt, unused borrowing capacity \| €						€ 1,600,000,000.0
Debt, borrowing capacity \| €						€ 2,500,000,000.0
Debt, renewal period		This program replaced an expiring program in the second quarter of 2020 and is renewable annually through the filing of a new listing.
PACCAR's Mexico finance subsidiary \| Commercial Paper
Debt Disclosure [Line Items]
Maximum limit of borrowing capacity	$ 5,000,000,000.0
PACCAR's Mexico finance subsidiary \| Commercial Paper \| Maximum
Debt Disclosure [Line Items]
Commercial paper expiration period	1 year
PACCAR's Mexico finance subsidiary \| Medium-term Notes
Debt Disclosure [Line Items]
Registration expiration		2021-04
Debt, unused borrowing capacity							$ 6,842,700,000
PACCAR's Mexico finance subsidiary \| Medium-term Notes \| Commercial Paper
Debt Disclosure [Line Items]
Debt, borrowing capacity	$ 10,000,000,000.0
PACCAR's Australian subsidiary \| Medium-term Notes
Debt Disclosure [Line Items]
Debt outstanding		$ 450.0
Financial Services
Debt Disclosure [Line Items]
Commercial paper and term notes borrowings		10,622.4	10,909.7
Fair value hedges and unamortized discounts, net		$ (12.7)	$ (20.5)