Finance Receivables Summary by those Evaluated Collectively and Individually (Detail) (Financial Services, USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually	$ 58.5	$ 71.1
Allowance for impaired finance receivables determined individually	9.1	13.0
Recorded investment for finance receivables evaluated collectively	8,649.2	8,245.2
Allowance for finance receivables determined collectively	113.9	111.4
Dealer wholesale financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually	9.1	3.6
Allowance for impaired finance receivables determined individually	1.5	2.2
Recorded investment for finance receivables evaluated collectively	1,727.1	1,537.4
Allowance for finance receivables determined collectively	9.4	9.6
Retail | Dealer
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually		0.1
Recorded investment for finance receivables evaluated collectively	1,403.3	1,429.6
Allowance for finance receivables determined collectively	12.6	13.4
Retail | Customer
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually	49.4	67.4
Allowance for impaired finance receivables determined individually	7.6	10.8
Recorded investment for finance receivables evaluated collectively	5,518.8	5,278.2
Allowance for finance receivables determined collectively	$ 91.9	$ 88.4