Carrying Amount and Fair Value for Fixed-Rate Loans and Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets:
Due from PACCAR and affiliates	$ 1,750.7	$ 1,905.3
Carrying Amount
Assets:
Fixed rate loans	5,380.4	4,779.4
Liabilities:
Fixed rate debt	6,084.5	5,826.1
Carrying Amount | Related Party
Assets:
Due from PACCAR and affiliates	956.0	1,101.0
Carrying Amount | Foreign Finance Affiliates
Assets:
Due from PACCAR and affiliates	559.0	554.0
Fair Value
Assets:
Fixed rate loans	5,324.4	4,566.4
Liabilities:
Fixed rate debt	6,005.8	5,559.0
Fair Value | Related Party
Assets:
Due from PACCAR and affiliates	941.7	1,048.2
Fair Value | Foreign Finance Affiliates
Assets:
Due from PACCAR and affiliates	$ 536.5	$ 516.6