Other Operating Expenses (Details Of Other Operating Expenses) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Expenses [Abstract]
Insurance Commissions	$ 374us-gaap_InsuranceCommissions	$ 370us-gaap_InsuranceCommissions	$ 382us-gaap_InsuranceCommissions
Communications and Information Technology	334	346	317
Lease and loan administration	122ally_LeaseAndLoanAdministration	173ally_LeaseAndLoanAdministration	325ally_LeaseAndLoanAdministration
Marketing and Advertising Expense	111us-gaap_MarketingAndAdvertisingExpense	136us-gaap_MarketingAndAdvertisingExpense	145us-gaap_MarketingAndAdvertisingExpense
Professional Fees	100us-gaap_ProfessionalFees	176us-gaap_ProfessionalFees	149us-gaap_ProfessionalFees
Regulatory and licensing fees	87	116	118
Vehicle remarketing and repossession	83ally_VehicleRemarketingAndRepossession	60ally_VehicleRemarketingAndRepossession	52ally_VehicleRemarketingAndRepossession
Depreciation, Nonproduction	81us-gaap_DepreciationNonproduction	81us-gaap_DepreciationNonproduction	76us-gaap_DepreciationNonproduction
Occupancy, Net	47us-gaap_OccupancyNet	44us-gaap_OccupancyNet	50us-gaap_OccupancyNet
Legal Fees	4us-gaap_LegalFees	105us-gaap_LegalFees	6us-gaap_LegalFees
Mortgage Representation And Warranty, Net	(10)	104	171
Other Cost and Expense, Operating	258us-gaap_OtherCostAndExpenseOperating	270us-gaap_OtherCostAndExpenseOperating	271us-gaap_OtherCostAndExpenseOperating
Total other operating expenses	1,591us-gaap_OtherNoninterestExpense	1,981us-gaap_OtherNoninterestExpense	2,062us-gaap_OtherNoninterestExpense
CFPB Settlement		$ 98ally_CFPBSettlement

CFPB Settlement

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Lease and loan administration.

+ References

No definition available.

+ Details

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Namespace Prefix:	ally_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Mortgage representation and warranty, net.

+ References

No definition available.

+ Details

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Namespace Prefix:	ally_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Vehicle remarketing and repossession.

+ References

No definition available.

+ Details

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Namespace Prefix:	ally_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of expense in the period for communications and data processing expense.

+ References

+ Details

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

- Definition

The expense recognized in the current period that allocates the cost of nonproduction tangible assets over their useful lives.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

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

- Definition

Amount of expense for Federal Deposit Insurance Corporation (FDIC) insurance.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.14)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

The expense incurred by an insurance company to persons or entities for generating or placing insurance or investment contracts with the company, usually determined as a percentage of policy or contract premiums. Excludes advances or draws to be applied against commissions earned.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.7(a))

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of expense provided in the period for legal costs incurred on or before the balance sheet date pertaining to resolved, pending or threatened litigation, including arbitration and mediation proceedings.

+ References

+ Details

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

- Definition

The total expense recognized in the period for promotion, public relations, and brand or product advertising.

+ References

+ Details

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

- Definition

Amount of net occupancy expense that may include items, such as depreciation of facilities and equipment, lease expenses, property taxes and property and casualty insurance expense.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.6)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 30

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.14(b))

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_OperatingExpensesAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of other operating cost and expense items that are associated with the entity's normal revenue producing operation.

+ References

+ Details

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

- Definition

Other noninterest expenses that are not separately presented in any other noninterest expense category.

+ References

+ Details

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

- Definition

A fee charged for services from professionals such as doctors, lawyers and accountants. The term is often expanded to include other professions, for example, pharmacists charging to maintain a medicinal profile of a client or customer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.6-07.2(a),(b),(c),(d))

-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 225

-Section 45

-Paragraph 3

-Subparagraph (k)

-URI http://asc.fasb.org/extlink&oid=6488370&loc=d3e13550-115849

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Balance Type:	debit
Period Type:	duration