Amortized Cost Basis of Finance Receivables by Credit Quality Indicator and Portfolio Class (Detail) - Financial Services - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	$ 1,393.2	$ 2,033.1
Financed Receivables, By Origination Year, Current Fiscal Year	3,020.0	3,752.9
Financing Receivable, Originated One Year before Current Fiscal Year	2,943.2	2,843.0
Financing Receivable, Originated Two Years before Current Fiscal Year	2,138.9	1,736.5
Financing Receivable, Originated Three Years before Current Fiscal Year	1,124.0	840.4
Financing Receivable, Originated Four Years before Current Fiscal Year	496.0	381.5
Financed Receivables, By Origination Year, Prior	261.3	208.8
Finance Receivables, Total	11,376.6	11,796.2
Dealer
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	1,393.2	2,033.1
Financed Receivables, By Origination Year, Current Fiscal Year	335.7	509.4
Financing Receivable, Originated One Year before Current Fiscal Year	375.9	485.4
Financing Receivable, Originated Two Years before Current Fiscal Year	427.3	272.5
Financing Receivable, Originated Three Years before Current Fiscal Year	231.2	181.5
Financing Receivable, Originated Four Years before Current Fiscal Year	153.0	101.6
Financed Receivables, By Origination Year, Prior	138.7	132.0
Finance Receivables, Total	3,055.0	3,715.5
Dealer | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	1,377.1	2,012.4
Finance Receivables, Total	1,377.1	2,012.4
Dealer | Wholesale | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	1,371.8	2,004.5
Finance Receivables, Total	1,371.8	2,004.5
Dealer | Wholesale | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	5.3	7.9
Finance Receivables, Total	5.3	7.9
Dealer | Retail
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	16.1	20.7
Financed Receivables, By Origination Year, Current Fiscal Year	335.7	509.4
Financing Receivable, Originated One Year before Current Fiscal Year	375.9	485.4
Financing Receivable, Originated Two Years before Current Fiscal Year	427.3	272.5
Financing Receivable, Originated Three Years before Current Fiscal Year	231.2	181.5
Financing Receivable, Originated Four Years before Current Fiscal Year	153.0	101.6
Financed Receivables, By Origination Year, Prior	138.7	132.0
Finance Receivables, Total	1,677.9	1,703.1
Dealer | Retail | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	16.1	20.7
Financed Receivables, By Origination Year, Current Fiscal Year	329.8	504.2
Financing Receivable, Originated One Year before Current Fiscal Year	372.1	474.9
Financing Receivable, Originated Two Years before Current Fiscal Year	417.8	268.0
Financing Receivable, Originated Three Years before Current Fiscal Year	226.5	180.1
Financing Receivable, Originated Four Years before Current Fiscal Year	151.8	100.4
Financed Receivables, By Origination Year, Prior	137.5	132.0
Finance Receivables, Total	1,651.6	1,680.3
Dealer | Retail | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	5.9	5.2
Financing Receivable, Originated One Year before Current Fiscal Year	3.8	10.5
Financing Receivable, Originated Two Years before Current Fiscal Year	9.5	4.5
Financing Receivable, Originated Three Years before Current Fiscal Year	4.7	1.4
Financing Receivable, Originated Four Years before Current Fiscal Year	1.2
Finance Receivables, Total	25.1	21.6
Dealer | Retail | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Originated Four Years before Current Fiscal Year		1.2
Financed Receivables, By Origination Year, Prior	1.2
Finance Receivables, Total	1.2	1.2
Customer Retail
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	2,684.3	3,243.5
Financing Receivable, Originated One Year before Current Fiscal Year	2,567.3	2,357.6
Financing Receivable, Originated Two Years before Current Fiscal Year	1,711.6	1,464.0
Financing Receivable, Originated Three Years before Current Fiscal Year	892.8	658.9
Financing Receivable, Originated Four Years before Current Fiscal Year	343.0	279.9
Financed Receivables, By Origination Year, Prior	122.6	76.8
Finance Receivables, Total	8,321.6	8,080.7
Customer Retail | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	2,170.5	2,686.4
Financing Receivable, Originated One Year before Current Fiscal Year	2,135.3	1,976.4
Financing Receivable, Originated Two Years before Current Fiscal Year	1,445.4	1,233.7
Financing Receivable, Originated Three Years before Current Fiscal Year	751.6	551.8
Financing Receivable, Originated Four Years before Current Fiscal Year	292.6	238.1
Financed Receivables, By Origination Year, Prior	110.1	67.2
Finance Receivables, Total	6,905.5	6,753.6
Customer Retail | Fleet | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	2,164.2	2,664.9
Financing Receivable, Originated One Year before Current Fiscal Year	2,123.1	1,921.6
Financing Receivable, Originated Two Years before Current Fiscal Year	1,411.1	1,203.7
Financing Receivable, Originated Three Years before Current Fiscal Year	732.8	533.7
Financing Receivable, Originated Four Years before Current Fiscal Year	286.5	234.2
Financed Receivables, By Origination Year, Prior	109.1	65.2
Finance Receivables, Total	6,826.8	6,623.3
Customer Retail | Fleet | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	1.4	13.5
Financing Receivable, Originated One Year before Current Fiscal Year	5.0	17.8
Financing Receivable, Originated Two Years before Current Fiscal Year	4.6	11.8
Financing Receivable, Originated Three Years before Current Fiscal Year	7.1	5.9
Financing Receivable, Originated Four Years before Current Fiscal Year	0.6	1.5
Financed Receivables, By Origination Year, Prior	0.2	1.2
Finance Receivables, Total	18.9	51.7
Customer Retail | Fleet | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	4.9	8.0
Financing Receivable, Originated One Year before Current Fiscal Year	7.2	37.0
Financing Receivable, Originated Two Years before Current Fiscal Year	29.7	18.2
Financing Receivable, Originated Three Years before Current Fiscal Year	11.7	12.2
Financing Receivable, Originated Four Years before Current Fiscal Year	5.5	2.4
Financed Receivables, By Origination Year, Prior	0.8	0.8
Finance Receivables, Total	59.8	78.6
Customer Retail | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	513.8	557.1
Financing Receivable, Originated One Year before Current Fiscal Year	432.0	381.2
Financing Receivable, Originated Two Years before Current Fiscal Year	266.2	230.3
Financing Receivable, Originated Three Years before Current Fiscal Year	141.2	107.1
Financing Receivable, Originated Four Years before Current Fiscal Year	50.4	41.8
Financed Receivables, By Origination Year, Prior	12.5	9.6
Finance Receivables, Total	1,416.1	1,327.1
Customer Retail | Owner/Operator | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	512.9	554.6
Financing Receivable, Originated One Year before Current Fiscal Year	429.7	376.4
Financing Receivable, Originated Two Years before Current Fiscal Year	262.3	225.1
Financing Receivable, Originated Three Years before Current Fiscal Year	137.9	105.2
Financing Receivable, Originated Four Years before Current Fiscal Year	49.7	41.2
Financed Receivables, By Origination Year, Prior	12.3	9.1
Finance Receivables, Total	1,404.8	1,311.6
Customer Retail | Owner/Operator | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	0.6	1.6
Financing Receivable, Originated One Year before Current Fiscal Year	0.9	2.7
Financing Receivable, Originated Two Years before Current Fiscal Year	2.0	2.0
Financing Receivable, Originated Three Years before Current Fiscal Year	0.8	0.7
Financing Receivable, Originated Four Years before Current Fiscal Year	0.1	0.2
Financed Receivables, By Origination Year, Prior		0.2
Finance Receivables, Total	4.4	7.4
Customer Retail | Owner/Operator | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	0.3	0.9
Financing Receivable, Originated One Year before Current Fiscal Year	1.4	2.1
Financing Receivable, Originated Two Years before Current Fiscal Year	1.9	3.2
Financing Receivable, Originated Three Years before Current Fiscal Year	2.5	1.2
Financing Receivable, Originated Four Years before Current Fiscal Year	0.6	0.4
Financed Receivables, By Origination Year, Prior	0.2	0.3
Finance Receivables, Total	$ 6.9	$ 8.1