Securitizations and Variable Interest Entities (Schedule of Variable Interest Entities) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale, Gain (Loss) on Sale	$ 2	$ 0	$ (3)
Assets of nonconsolidated variable interest entities	1,964	2,899
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	2,791	3,574
Carrying value of assets for VIEs for which we have continuing involvement	30,776	37,631
Carrying value of liabilities for VIEs for which we have continuing involvement	10,483	13,490
Commercial Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	592	460
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	248	169
Assets of nonconsolidated variable interest entities	0	0
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	790	651
Automobile Loan [Member] \| Consumer Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	17,597	20,869
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	7,677	8,557
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	37	24
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0	0
Assets of nonconsolidated variable interest entities	1,964	2,899
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	2,001	2,923
Automobile Loan [Member] \| Consumer Portfolio Segment [Member] \| Held-to-maturity Securities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	36
Automobile Loan [Member] \| Consumer Portfolio Segment [Member] \| Other Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	1
Automobile Loan [Member] \| Commercial Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	12,550	16,278
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	2,558	4,764
Unencumbered [Member] \| Automobile Loan [Member] \| Consumer Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	8,527	9,600
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ 29	$ 50

Assets of nonconsolidated variable interest entities

No definition available.

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- Definition

The carrying amount of the assets in the reporting entity's statement of financial position that relate to consolidated and nonconsolidated Variable Interest Entities.

+ References

No definition available.

+ Details

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- Definition

Carrying value of liabilities for VIEs for which we have continuing involvement

+ References

No definition available.

+ Details

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- Definition

Reflects, by transferred financial asset type, the amount of sales proceeds in excess of or deficient from the sum of the carrying amounts of transferred financial assets plus transaction costs, including those transactions in which the seller/transferor has continuing involvement with the financial assets that have been transferred.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107207-111719

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 10
-Section 40
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=65892426&loc=d3e96813-111708

+ Details

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- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5710-111685

+ Details

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- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

+ Details

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- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5728-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5747-111685

+ Details

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- 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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- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

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- Definition

Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

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- Details

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- Details

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