Pre-Tax Effects of Gain (Loss) on Cash Flow Hedges Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 33.7	$ 55.7
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	0.3	70.6
Truck, Parts and Other \| Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	2.1	70.6
Financial Services \| Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	33.7	$ 55.7
Financial Services \| Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ (1.8)

Amount before tax and reclassification adjustments of other comprehensive income (loss).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 45
-Paragraph 20
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 45
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118261656&loc=d3e32136-110900

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580

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