Amortized Cost Basis of Finance Receivables by Credit Quality Indicator and Portfolio Class (Detail) - Financial Services - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	$ 1,836.6	$ 2,033.1
Financed Receivables, By Origination Year, Current Fiscal Year	2,195.7	3,752.9
Financing Receivable, Originated One Year before Current Fiscal Year	3,216.7	2,843.0
Financing Receivable, Originated Two Years before Current Fiscal Year	2,368.9	1,736.5
Financing Receivable, Originated Three Years before Current Fiscal Year	1,316.3	840.4
Financing Receivable, Originated Four Years before Current Fiscal Year	600.2	381.5
Financed Receivables, By Origination Year, Prior	338.3	208.8
Finance Receivables, Total	11,872.7	11,796.2
Dealer
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	1,836.6	2,033.1
Financed Receivables, By Origination Year, Current Fiscal Year	269.7	509.4
Financing Receivable, Originated One Year before Current Fiscal Year	388.0	485.4
Financing Receivable, Originated Two Years before Current Fiscal Year	434.2	272.5
Financing Receivable, Originated Three Years before Current Fiscal Year	236.5	181.5
Financing Receivable, Originated Four Years before Current Fiscal Year	158.7	101.6
Financed Receivables, By Origination Year, Prior	161.4	132.0
Finance Receivables, Total	3,485.1	3,715.5
Dealer | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	1,818.3	2,012.4
Finance Receivables, Total	1,818.3	2,012.4
Dealer | Wholesale | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	1,811.1	2,004.5
Finance Receivables, Total	1,811.1	2,004.5
Dealer | Wholesale | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	7.2	7.9
Finance Receivables, Total	7.2	7.9
Dealer | Retail
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	18.3	20.7
Financed Receivables, By Origination Year, Current Fiscal Year	269.7	509.4
Financing Receivable, Originated One Year before Current Fiscal Year	388.0	485.4
Financing Receivable, Originated Two Years before Current Fiscal Year	434.2	272.5
Financing Receivable, Originated Three Years before Current Fiscal Year	236.5	181.5
Financing Receivable, Originated Four Years before Current Fiscal Year	158.7	101.6
Financed Receivables, By Origination Year, Prior	161.4	132.0
Finance Receivables, Total	1,666.8	1,703.1
Dealer | Retail | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	18.3	20.7
Financed Receivables, By Origination Year, Current Fiscal Year	266.7	504.2
Financing Receivable, Originated One Year before Current Fiscal Year	384.1	474.9
Financing Receivable, Originated Two Years before Current Fiscal Year	424.4	268.0
Financing Receivable, Originated Three Years before Current Fiscal Year	232.5	180.1
Financing Receivable, Originated Four Years before Current Fiscal Year	157.4	100.4
Financed Receivables, By Origination Year, Prior	160.1	132.0
Finance Receivables, Total	1,643.5	1,680.3
Dealer | Retail | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	3.0	5.2
Financing Receivable, Originated One Year before Current Fiscal Year	3.9	10.5
Financing Receivable, Originated Two Years before Current Fiscal Year	9.8	4.5
Financing Receivable, Originated Three Years before Current Fiscal Year	4.0	1.4
Financing Receivable, Originated Four Years before Current Fiscal Year	1.3
Finance Receivables, Total	22.0	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	1.3
Finance Receivables, Total	1.3	1.2
Customer Retail
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	1,926.0	3,243.5
Financing Receivable, Originated One Year before Current Fiscal Year	2,828.7	2,357.6
Financing Receivable, Originated Two Years before Current Fiscal Year	1,934.7	1,464.0
Financing Receivable, Originated Three Years before Current Fiscal Year	1,079.8	658.9
Financing Receivable, Originated Four Years before Current Fiscal Year	441.5	279.9
Financed Receivables, By Origination Year, Prior	176.9	76.8
Finance Receivables, Total	8,387.6	8,080.7
Customer Retail | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	1,549.2	2,686.4
Financing Receivable, Originated One Year before Current Fiscal Year	2,349.5	1,976.4
Financing Receivable, Originated Two Years before Current Fiscal Year	1,625.9	1,233.7
Financing Receivable, Originated Three Years before Current Fiscal Year	908.4	551.8
Financing Receivable, Originated Four Years before Current Fiscal Year	371.1	238.1
Financed Receivables, By Origination Year, Prior	152.3	67.2
Finance Receivables, Total	6,956.4	6,753.6
Customer Retail | Fleet | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	1,542.7	2,664.9
Financing Receivable, Originated One Year before Current Fiscal Year	2,332.3	1,921.6
Financing Receivable, Originated Two Years before Current Fiscal Year	1,584.7	1,203.7
Financing Receivable, Originated Three Years before Current Fiscal Year	889.0	533.7
Financing Receivable, Originated Four Years before Current Fiscal Year	362.9	234.2
Financed Receivables, By Origination Year, Prior	150.2	65.2
Finance Receivables, Total	6,861.8	6,623.3
Customer Retail | Fleet | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	1.5	13.5
Financing Receivable, Originated One Year before Current Fiscal Year	8.1	17.8
Financing Receivable, Originated Two Years before Current Fiscal Year	11.1	11.8
Financing Receivable, Originated Three Years before Current Fiscal Year	6.7	5.9
Financing Receivable, Originated Four Years before Current Fiscal Year	1.8	1.5
Financed Receivables, By Origination Year, Prior	1.2	1.2
Finance Receivables, Total	30.4	51.7
Customer Retail | Fleet | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	5.0	8.0
Financing Receivable, Originated One Year before Current Fiscal Year	9.1	37.0
Financing Receivable, Originated Two Years before Current Fiscal Year	30.1	18.2
Financing Receivable, Originated Three Years before Current Fiscal Year	12.7	12.2
Financing Receivable, Originated Four Years before Current Fiscal Year	6.4	2.4
Financed Receivables, By Origination Year, Prior	0.9	0.8
Finance Receivables, Total	64.2	78.6
Customer Retail | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	376.8	557.1
Financing Receivable, Originated One Year before Current Fiscal Year	479.2	381.2
Financing Receivable, Originated Two Years before Current Fiscal Year	308.8	230.3
Financing Receivable, Originated Three Years before Current Fiscal Year	171.4	107.1
Financing Receivable, Originated Four Years before Current Fiscal Year	70.4	41.8
Financed Receivables, By Origination Year, Prior	24.6	9.6
Finance Receivables, Total	1,431.2	1,327.1
Customer Retail | Owner/Operator | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	376.5	554.6
Financing Receivable, Originated One Year before Current Fiscal Year	475.7	376.4
Financing Receivable, Originated Two Years before Current Fiscal Year	305.2	225.1
Financing Receivable, Originated Three Years before Current Fiscal Year	167.8	105.2
Financing Receivable, Originated Four Years before Current Fiscal Year	68.9	41.2
Financed Receivables, By Origination Year, Prior	24.2	9.1
Finance Receivables, Total	1,418.3	1,311.6
Customer Retail | Owner/Operator | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	0.2	1.6
Financing Receivable, Originated One Year before Current Fiscal Year	2.5	2.7
Financing Receivable, Originated Two Years before Current Fiscal Year	1.8	2.0
Financing Receivable, Originated Three Years before Current Fiscal Year	1.0	0.7
Financing Receivable, Originated Four Years before Current Fiscal Year	0.5	0.2
Financed Receivables, By Origination Year, Prior	0.1	0.2
Finance Receivables, Total	6.1	7.4
Customer Retail | Owner/Operator | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	0.1	0.9
Financing Receivable, Originated One Year before Current Fiscal Year	1.0	2.1
Financing Receivable, Originated Two Years before Current Fiscal Year	1.8	3.2
Financing Receivable, Originated Three Years before Current Fiscal Year	2.6	1.2
Financing Receivable, Originated Four Years before Current Fiscal Year	1.0	0.4
Financed Receivables, By Origination Year, Prior	0.3	0.3
Finance Receivables, Total	$ 6.8	$ 8.1