Carrying Amount and Fair Value for Fixed-Rate Loans and Debt (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets:
Due from PACCAR	$ 1,618.7	$ 1,581.3	[1]
Due from foreign finance affiliates	703.5	697.5
Carrying Amount
Assets:
Due from PACCAR	859.0	821.0
Due from foreign finance affiliates	472.0	472.0
Fixed rate loans	3,315.3	3,239.5
Liabilities:
Fixed rate debt	4,445.8	4,394.4
Fair Value
Assets:
Due from PACCAR	859.3	815.2
Due from foreign finance affiliates	477.0	474.2
Fixed rate loans	3,330.6	3,234.4
Liabilities:
Fixed rate debt	$ 4,444.1	$ 4,363.2

[1] The December 31, 2018 balance sheet has been derived from audited financial statements.