Amounts Outstanding Including Foreign Finance Affiliates (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Accounts Payable and Accrued Liabilities [Abstract]
Due to PACCAR and affiliates	$ 58.6	$ 21.8
Related Party [Member]
Accounts, Notes, Loans and Financing Receivable, Unclassified [Abstract]
Due from PACCAR and affiliates	1,750.7	1,905.3
Accounts Payable and Accrued Liabilities [Abstract]
Due to PACCAR and affiliates	58.6	21.8
Related Party [Member] | Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable, Unclassified [Abstract]
Loans due from PACCAR/ foreign affiliates	1,016.0	1,261.0
Tax-related receivable due from PACCAR		4.4
Accounts Payable and Accrued Liabilities [Abstract]
Tax-related payable due to PACCAR	1.9
Related Party [Member] | Foreign Finance Affiliates
Accounts, Notes, Loans and Financing Receivable, Unclassified [Abstract]
Loans due from PACCAR/ foreign affiliates	716.0	627.0
Related Party [Member] | Other Affiliates [Member]
Accounts, Notes, Loans and Financing Receivable, Unclassified [Abstract]
Receivables	18.7	12.9
Accounts Payable and Accrued Liabilities [Abstract]
Accounts Payable	$ 56.7	$ 21.8