Amortized Cost Basis of Finance Receivables by Credit Quality Indicator and Portfolio Class (Detail) - Financial Services - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	$ 1,958.8	$ 2,033.1
Financed Receivables, By Origination Year, Current Fiscal Year	955.4	3,752.9
Financing Receivable, Originated One Year before Current Fiscal Year	3,477.9	2,843.0
Financing Receivable, Originated Two Years before Current Fiscal Year	2,606.0	1,736.5
Financing Receivable, Originated Three Years before Current Fiscal Year	1,531.1	840.4
Financing Receivable, Originated Four Years before Current Fiscal Year	712.3	381.5
Financed Receivables, By Origination Year, Prior	463.3	208.8
Finance Receivables, Total	11,704.8	11,796.2
Dealer
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	1,958.8	2,033.1
Financed Receivables, By Origination Year, Current Fiscal Year	65.7	509.4
Financing Receivable, Originated One Year before Current Fiscal Year	431.3	485.4
Financing Receivable, Originated Two Years before Current Fiscal Year	479.8	272.5
Financing Receivable, Originated Three Years before Current Fiscal Year	270.6	181.5
Financing Receivable, Originated Four Years before Current Fiscal Year	176.9	101.6
Financed Receivables, By Origination Year, Prior	211.0	132.0
Finance Receivables, Total	3,594.1	3,715.5
Dealer | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	1,939.8	2,012.4
Finance Receivables, Total	1,939.8	2,012.4
Dealer | Wholesale | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	1,933.7	2,004.5
Finance Receivables, Total	1,933.7	2,004.5
Dealer | Wholesale | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	6.1	7.9
Finance Receivables, Total	6.1	7.9
Dealer | Retail
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	19.0	20.7
Financed Receivables, By Origination Year, Current Fiscal Year	65.7	509.4
Financing Receivable, Originated One Year before Current Fiscal Year	431.3	485.4
Financing Receivable, Originated Two Years before Current Fiscal Year	479.8	272.5
Financing Receivable, Originated Three Years before Current Fiscal Year	270.6	181.5
Financing Receivable, Originated Four Years before Current Fiscal Year	176.9	101.6
Financed Receivables, By Origination Year, Prior	211.0	132.0
Finance Receivables, Total	1,654.3	1,703.1
Dealer | Retail | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Loans	19.0	20.7
Financed Receivables, By Origination Year, Current Fiscal Year	65.3	504.2
Financing Receivable, Originated One Year before Current Fiscal Year	427.1	474.9
Financing Receivable, Originated Two Years before Current Fiscal Year	469.6	268.0
Financing Receivable, Originated Three Years before Current Fiscal Year	265.5	180.1
Financing Receivable, Originated Four Years before Current Fiscal Year	175.6	100.4
Financed Receivables, By Origination Year, Prior	209.9	132.0
Finance Receivables, Total	1,632.0	1,680.3
Dealer | Retail | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	0.4	5.2
Financing Receivable, Originated One Year before Current Fiscal Year	4.2	10.5
Financing Receivable, Originated Two Years before Current Fiscal Year	10.2	4.5
Financing Receivable, Originated Three Years before Current Fiscal Year	5.1	1.4
Financing Receivable, Originated Four Years before Current Fiscal Year	1.3
Finance Receivables, Total	21.2	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	1.1
Finance Receivables, Total	1.1	1.2
Customer Retail
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	889.7	3,243.5
Financing Receivable, Originated One Year before Current Fiscal Year	3,046.6	2,357.6
Financing Receivable, Originated Two Years before Current Fiscal Year	2,126.2	1,464.0
Financing Receivable, Originated Three Years before Current Fiscal Year	1,260.5	658.9
Financing Receivable, Originated Four Years before Current Fiscal Year	535.4	279.9
Financed Receivables, By Origination Year, Prior	252.3	76.8
Finance Receivables, Total	8,110.7	8,080.7
Customer Retail | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	711.4	2,686.4
Financing Receivable, Originated One Year before Current Fiscal Year	2,528.8	1,976.4
Financing Receivable, Originated Two Years before Current Fiscal Year	1,784.4	1,233.7
Financing Receivable, Originated Three Years before Current Fiscal Year	1,062.2	551.8
Financing Receivable, Originated Four Years before Current Fiscal Year	449.5	238.1
Financed Receivables, By Origination Year, Prior	217.8	67.2
Finance Receivables, Total	6,754.1	6,753.6
Customer Retail | Fleet | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	705.8	2,664.9
Financing Receivable, Originated One Year before Current Fiscal Year	2,505.8	1,921.6
Financing Receivable, Originated Two Years before Current Fiscal Year	1,736.6	1,203.7
Financing Receivable, Originated Three Years before Current Fiscal Year	1,037.6	533.7
Financing Receivable, Originated Four Years before Current Fiscal Year	439.1	234.2
Financed Receivables, By Origination Year, Prior	214.3	65.2
Finance Receivables, Total	6,639.2	6,623.3
Customer Retail | Fleet | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	1.6	13.5
Financing Receivable, Originated One Year before Current Fiscal Year	14.6	17.8
Financing Receivable, Originated Two Years before Current Fiscal Year	15.2	11.8
Financing Receivable, Originated Three Years before Current Fiscal Year	9.1	5.9
Financing Receivable, Originated Four Years before Current Fiscal Year	2.5	1.5
Financed Receivables, By Origination Year, Prior	1.5	1.2
Finance Receivables, Total	44.5	51.7
Customer Retail | Fleet | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	4.0	8.0
Financing Receivable, Originated One Year before Current Fiscal Year	8.4	37.0
Financing Receivable, Originated Two Years before Current Fiscal Year	32.6	18.2
Financing Receivable, Originated Three Years before Current Fiscal Year	15.5	12.2
Financing Receivable, Originated Four Years before Current Fiscal Year	7.9	2.4
Financed Receivables, By Origination Year, Prior	2.0	0.8
Finance Receivables, Total	70.4	78.6
Customer Retail | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	178.3	557.1
Financing Receivable, Originated One Year before Current Fiscal Year	517.8	381.2
Financing Receivable, Originated Two Years before Current Fiscal Year	341.8	230.3
Financing Receivable, Originated Three Years before Current Fiscal Year	198.3	107.1
Financing Receivable, Originated Four Years before Current Fiscal Year	85.9	41.8
Financed Receivables, By Origination Year, Prior	34.5	9.6
Finance Receivables, Total	1,356.6	1,327.1
Customer Retail | Owner/Operator | Performing
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year	178.2	554.6
Financing Receivable, Originated One Year before Current Fiscal Year	514.7	376.4
Financing Receivable, Originated Two Years before Current Fiscal Year	337.8	225.1
Financing Receivable, Originated Three Years before Current Fiscal Year	194.1	105.2
Financing Receivable, Originated Four Years before Current Fiscal Year	84.0	41.2
Financed Receivables, By Origination Year, Prior	33.9	9.1
Finance Receivables, Total	1,342.7	1,311.6
Customer Retail | Owner/Operator | Watch
Financing Receivable, Recorded Investment [Line Items]
Financed Receivables, By Origination Year, Current Fiscal Year		1.6
Financing Receivable, Originated One Year before Current Fiscal Year	2.4	2.7
Financing Receivable, Originated Two Years before Current Fiscal Year	2.1	2.0
Financing Receivable, Originated Three Years before Current Fiscal Year	1.4	0.7
Financing Receivable, Originated Four Years before Current Fiscal Year	0.5	0.2
Financed Receivables, By Origination Year, Prior	0.2	0.2
Finance Receivables, Total	6.6	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	0.7	2.1
Financing Receivable, Originated Two Years before Current Fiscal Year	1.9	3.2
Financing Receivable, Originated Three Years before Current Fiscal Year	2.8	1.2
Financing Receivable, Originated Four Years before Current Fiscal Year	1.4	0.4
Financed Receivables, By Origination Year, Prior	0.4	0.3
Finance Receivables, Total	$ 7.3	$ 8.1