Fair Value Fair Value (Summary of Fair Value and Carrying Value of Company Financial Instruments) (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 24, 2017
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Finance receivables, net	$ 7,394,684	$ 7,021,549	$ 7,159,632
Fair Value \| Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Short-term Debt, Fair Value	1,373,859	1,273,482	834,875
Fair Value \| Medium-term notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	4,386,030	4,189,092	4,612,083
Fair Value \| Senior unsecured notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	707,252	784,433	774,693
Fair Value \| Secured Debt \| Asset-Backed U.S. Commercial Paper Conduit Facility VIE
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	265,044	279,457	280,308
Fair Value \| Secured Debt \| Asset-backed Canadian commercial paper conduit facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	149,418	174,779	122,130
Fair Value \| Secured Debt \| Asset-backed securitization debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	127,906	351,767	430,038
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Finance receivables, net	7,303,562	6,965,086	7,101,025
Reported Value Measurement [Member] \| Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Short-term Debt, Fair Value	1,373,859	1,273,482	834,875
Reported Value Measurement [Member] \| Medium-term notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	4,437,279	4,165,706	4,564,124
Reported Value Measurement [Member] \| Senior unsecured notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	742,458	741,961	741,797
Reported Value Measurement [Member] \| Secured Debt \| Asset-Backed U.S. Commercial Paper Conduit Facility VIE
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	265,044	279,457	280,308
Reported Value Measurement [Member] \| Secured Debt \| Asset-backed Canadian commercial paper conduit facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	149,418	174,779	122,130
Reported Value Measurement [Member] \| Secured Debt \| Asset-backed securitization debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	$ 128,474	$ 352,624	$ 429,833

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13476-108611

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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- Details

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- Details

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