Asset-Backed Financing (Narrative) (Detail)	1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2016 CAD	Jun. 26, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 14, 2016 USD ($)
Variable Interest Entity [Line Items]
Company issued secured notes, net of discount and issuance costs			$ 5,714,527,000	$ 5,751,859,000
Financial Services interest expense			180,193,000	173,756,000	$ 161,983,000
Servicing and ancillary fees			1,900,000	1,600,000
Secured Debt
Variable Interest Entity [Line Items]
Company issued secured notes, net of discount and issuance costs			806,860,000	945,613,000
Variable Interest Entity, Primary Beneficiary | Secured Debt
Variable Interest Entity [Line Items]
Financial Services interest expense			$ 7,900,000	$ 13,100,000
Weighted average interest rate at date of issuance			1.53%	1.31%
Variable Interest Entity, Primary Beneficiary | Secured Debt | Secured Notes Issued January 2015
Variable Interest Entity [Line Items]
Company issued secured notes			$ 700,000,000
Weighted average interest rate at date of issuance			0.89%
Variable Interest Entity, Primary Beneficiary | Secured Debt | Term asset-backed securitizations
Variable Interest Entity [Line Items]
Company issued secured notes			$ 500,000,000
Weighted average interest rate at date of issuance			0.88%
Variable Interest Entity, Primary Beneficiary | Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE | Line of Credit
Variable Interest Entity [Line Items]
Financial Services interest expense			$ 7,100,000	$ 1,300,000
Weighted average interest rate at date of issuance			2.33%
Variable Interest Entity, Primary Beneficiary | Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE | U.S. Line of Credit
Variable Interest Entity [Line Items]
Company issued secured notes			$ 383,300,000
Line of credit, maximum borrowing capacity						$ 900,000,000
Borrowings outstanding under conduit facility				0
Debt instrument, term			5 years
Transfers on finance receivables			$ 429,700,000
Variable Interest Entity, Primary Beneficiary | Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE, Facility 1 | U.S. Line of Credit
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity						600,000,000
Variable Interest Entity, Primary Beneficiary | Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE, Facility 2 | U.S. Line of Credit
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity						$ 300,000,000
Unconsolidated VIEs
Variable Interest Entity [Line Items]
Principal balance of finance receivable		$ 301,800,000
Gain on sale of finance receivable		9,300,000
Cash proceeds from sale of financial asset		$ 312,600,000
Unpaid principal balance of the retail motorcycle finance receivables			146,400,000
Unconsolidated VIEs | Secured Debt | Asset-backed Canadian commercial paper conduit facility
Variable Interest Entity [Line Items]
Financial Services interest expense			$ 2,600,000	$ 2,700,000
Weighted average interest rate at date of issuance			1.96%	1.84%
Unconsolidated VIEs | Secured Debt | Asset-backed Canadian commercial paper conduit facility | Foreign Line of Credit
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity | CAD	CAD 220,000,000
Debt instrument, term	5 years
Transfers on finance receivables			$ 105,400,000	$ 71,100,000
Amount transferred, face amount			87,000,000	$ 62,400,000
VIE, maximum loss exposure, amount			$ 35,600,000