Finance Receivables Summary by those Evaluated Collectively and Individually (Detail) (Financial Services, USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually	$ 86.2	$ 114.4
Allowance for impaired finance receivables determined individually	21.5	27.9
Recorded investment for finance receivables evaluated collectively	8,074.4	7,173.3
Allowance for finance receivables determined collectively	111.5	102.3
Dealer wholesale financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually	3.3	18.4
Allowance for impaired finance receivables determined individually	2.2	2.2
Recorded investment for finance receivables evaluated collectively	1,699.1	1,498.7
Allowance for finance receivables determined collectively	10.2	9.5
Retail
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually	82.9	96.0
Allowance for impaired finance receivables determined individually	19.3	25.7
Recorded investment for finance receivables evaluated collectively	6,375.3	5,674.6
Allowance for finance receivables determined collectively	$ 101.3	$ 92.8