Servicing Activities (Schedule Of Servicing Assets at Fair Value) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Servicing Activities [Abstract]
Estimated fair value, Beginning Balance	$ 0us-gaap_ServicingAssetAtFairValueAmount	$ 952us-gaap_ServicingAssetAtFairValueAmount
Servicing Asset at Fair Value, Additions	0	60
Servicing Asset at Fair Value, Changes in Fair Value Resulting from Changes in Valuation Inputs or Changes in Assumptions	0	(32)
Servicing Asset at Fair Value, Other Changes in Fair Value	0	(69)
Servicing Asset at Fair Value, Disposals	0	(911)
Estimated fair value, Ending Balance	$ 0us-gaap_ServicingAssetAtFairValueAmount	$ 0us-gaap_ServicingAssetAtFairValueAmount

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Namespace Prefix:	ally_
Data Type:	xbrli:stringItemType
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Period Type:	duration

The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

+ Details

Name:	us-gaap_ServicingAssetAtFairValueAdditions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The net Increase or Decrease in fair value as a result of changes in the inputs, assumptions, or model used to calculate the fair value of servicing assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(4)(i)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

+ Details

Name:	us-gaap_ServicingAssetAtFairValueChangesInFairValueResultingFromChangesInValuationInputsOrChangesInAssumptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Decrease in servicing assets subsequently measured at fair value resulting from conveyance of servicing rights to unrelated parties.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net Increase or Decrease in fair value as a result of other changes that are not additions, disposals, or a result of change in the inputs, assumptions, or model used to calculate the fair value of servicing assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(4)(ii)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

+ Details

Name:	us-gaap_ServicingAssetAtFairValueOtherChangesInFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration