Finance Receivables Summary by those Evaluated Collectively and Individually (Detail) (Financial Services, USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually	$ 72.0	$ 71.1
Allowance for impaired finance receivables determined individually	14.8	13.0
Recorded investment for finance receivables evaluated collectively	8,193.8	8,245.2
Allowance for finance receivables determined collectively	111.4	111.4
Dealer wholesale financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually	3.7	3.6
Allowance for impaired finance receivables determined individually	2.2	2.2
Recorded investment for finance receivables evaluated collectively	1,522.3	1,537.4
Allowance for finance receivables determined collectively	9.6	9.6
Retail | Customer
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment for impaired finance receivables evaluated individually	68.3	67.4
Allowance for impaired finance receivables determined individually	12.6	10.8
Recorded investment for finance receivables evaluated collectively	5,283.5	5,278.2
Allowance for finance receivables determined collectively	89.3	88.4
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	1,388.0	1,429.6
Allowance for finance receivables determined collectively	$ 12.5	$ 13.4