Finance Receivables and Loans, Net (Finance receivables and loans redefaulted during the period) (Details) - Consumer portfolio segment $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Consumer loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, subsequent default, number of loans	2,466	2,223	7,218	6,356
Financing receivable, modifications, subsequent default, gross carrying value	$ 27	$ 25	$ 84	$ 75
Financing receivables, impaired, troubled debt restructuring, charge-off amount	$ 19	$ 18	$ 54	$ 51
Automobile loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, subsequent default, number of loans	2,466	2,222	7,217	6,354
Financing receivable, modifications, subsequent default, gross carrying value	$ 27	$ 25	$ 84	$ 74
Financing receivables, impaired, troubled debt restructuring, charge-off amount	$ 19	$ 18	$ 54	$ 51
Mortgage Finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, subsequent default, number of loans	0	0	0	1
Financing receivable, modifications, subsequent default, gross carrying value	$ 0	$ 0	$ 0	$ 1
Financing receivables, impaired, troubled debt restructuring, charge-off amount	$ 0	$ 0	$ 0	$ 0
Mortgage - Legacy
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, subsequent default, number of loans	0	1	1	1
Financing receivable, modifications, subsequent default, gross carrying value	$ 0	$ 0	$ 0	$ 0
Financing receivables, impaired, troubled debt restructuring, charge-off amount	$ 0	$ 0	$ 0	$ 0

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

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- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
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