Securitizations And Variable Interest Entities (Schedule Of Cash Flow Received and Paid To Nonconsolidated Securitization Entities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Consumer Loans Auto Financing Receivable [Member]
Cash Flow Received and Paid to Nonconsolidated Securitization Entities [Line Items]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale, Gain (Loss) on Sale	$ 0	$ 0
Cash Flows Between Transferor and Transferee, Servicing Fees	7	2
Representations and warranties obligations		0
US Government-sponsored Enterprises [Member]
Cash Flow Received and Paid to Nonconsolidated Securitization Entities [Line Items]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale, Gain (Loss) on Sale	0	0
Cash Flows Between Transferor and Transferee, Servicing Fees	0	0
Representations and warranties obligations		$ 1

Cash Flow Between Transferee and Transferor representations and warranties obligations.

No definition available.

Name:	ally_CashFlowBetweenTransfereeAndTransferorRepresentationsAndWarrantiesObligations
Namespace Prefix:	ally_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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

- Definition

Cash Flows between a transferee and a transferor attributable to servicing fees related to a securitization, asset-backed financing arrangement, or similar transfer in which the transferor has continuing involvement with the transferred financial assets underlying the transaction (including, but not limited to, servicing, recourse, and restrictions on transferor's interests in the transferred financial assets).

+ References

+ Details

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

- 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=13989330&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=45353237&loc=d3e96813-111708

+ Details

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

- Details

Name:	us-gaap_ProductOrServiceAxis=ally_UsGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=us-gaap_ConsumerLoansAutoFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: