Bank holding companies with assets greater than $50 billion must develop and maintain a capital plan annually.

No definition available.

Name:	ally_AssetsGreaterThan50Billion
Namespace Prefix:	ally_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Common equity Tier 1 capital conservation buffer

+ References

No definition available.

+ Details

Name:	ally_CommonequityTier1capitalconservationbuffer
Namespace Prefix:	ally_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Common Equity Tier 1 Risk-based Capital required to be well capitalized to risk-weighted assets

+ References

No definition available.

+ Details

Name:	ally_CommonEquityTier1RiskbasedCapitalrequiredtobewellcapitalizedtoriskweightedassets
Namespace Prefix:	ally_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

FRB required reserve balance

+ References

No definition available.

+ Details

Name:	ally_FrbRequiredReserveBalance
Namespace Prefix:	ally_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	ally_RegulatoryMattersLineItems
Namespace Prefix:	ally_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Capital plan must include discussion of how bank holding companies will keep Tier 1 common ratio above 5 percent under certain conditions.

+ References

No definition available.

+ Details

Name:	ally_Tier1CommonRatioAbove5Percent
Namespace Prefix:	ally_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets in accordance with CLMA requirements for Ally Bank.

+ References

No definition available.

+ Details

Name:	ally_Tier1LeverageToAverageAssetsForAllyBank
Namespace Prefix:	ally_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ 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 210.5-02.18)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 12

-Article 7

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 18

-Article 5

+ Details

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

- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents disclosure of the total aggregate cash dividends paid to the entity by consolidated subsidiaries, by unconsolidated subsidiaries, and by 50% or less owned persons accounted for using the equity method.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 3

-Subparagraph (SX 210.12-04(b))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 235

-Section S99

-Paragraph 2

-Subparagraph (SX 210.9-06)

-URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537971-122884

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 06

-Article 9

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph b

-Article 12

+ Details

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

- Definition

Amount of dividends that can be declared or paid without approval of regulatory agency.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(e))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph e

-Article 4

+ Details

Name:	us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApproval
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	ally_U.S.FederalRegulatoryCapitalStandardAxis=ally_BaselIIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ally_U.S.FederalRegulatoryCapitalStandardAxis=ally_BaselIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ally_AllyBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ally_AllyFinancialIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ally_InsuranceOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Regulatory Capital (Regulatory Matters) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Regulatory Matters [Line Items]
assets greater than $50 billion	$ 50,000,000,000ally_AssetsGreaterThan50Billion
Assets	151,828,000,000us-gaap_Assets	151,167,000,000us-gaap_Assets	182,347,000,000us-gaap_Assets
Tier 1 Leverage To Average Assets For Ally Bank	15.00%
Insurance Operations [Member]
Regulatory Matters [Line Items]
Assets	7,190,000,000	7,124,000,000	8,439,000,000
Maximum dividend to be paid without statutory approval	106,000,000
Ally Bank [Member]
Regulatory Matters [Line Items]
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%
Total (to risk-weighted assets), Required minimum	8.00%
Tier 1 (to risk-weighted assets), Required minimum	4.00%
Assets	104,500,000,000	98,700,000,000
Cash Dividends Paid to Parent Company	1,800,000,000
FRB required reserve balance	$ 313,000,000	$ 416,000,000
Tier 1 Leverage To Average Assets For Ally Bank	15.00%
Parent Company [Member]
Regulatory Matters [Line Items]
Tier 1 common ratio above 5 percent	5.00%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%
Total (to risk-weighted assets), Required minimum	8.00%
Tier 1 (to risk-weighted assets), Required minimum	4.00%
Minimum [Member] \| Parent Company [Member]
Regulatory Matters [Line Items]
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	3.00%
Maximum [Member] \| Parent Company [Member]
Regulatory Matters [Line Items]
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%
Basel I [Member]
Regulatory Matters [Line Items]
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%
Total (to risk-weighted assets), Required minimum	8.00%
Tier 1 (to risk-weighted assets), Required minimum	4.00%
Basel I [Member] \| Minimum [Member]
Regulatory Matters [Line Items]
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	3.00%
Basel I [Member] \| Maximum [Member]
Regulatory Matters [Line Items]
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%
Basel III [Member]
Regulatory Matters [Line Items]
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	4.00%
Common equity Tier 1 capital conservation buffer	2.50%
Tier One Common Risk Based Capital	4.50%