Held for investment mortgage finance receivables interest only mortgage loans.

No definition available.

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

- Definition

Interest-only mortgage loan portfolio principal amortization

+ References

No definition available.

+ Details

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

- 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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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
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- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

+ Details

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

- Definition

Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

+ Details

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Period Type:	instant

Finance Receivables And Loans, Net (Schedule of Accounts, Notes, Loans and Financing Receivables) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derivative, Amount of Hedged Item	$ 537	$ 331
Finance receivables and loans, net	112,653	111,600	$ 105,172
Loans and Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	268	110
Fair Value Option Election, Fair Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net		111,600
Consumer Portfolio Segment [Member] \| Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net	74,365	74,065
Consumer Portfolio Segment [Member] \| Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net	63,281	64,292	60,786
Consumer Portfolio Segment [Member] \| Automobile Loan [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Contract [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derivative, Amount of Hedged Item	88	66
Consumer Portfolio Segment [Member] \| Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net	11,084	9,773	9,211
Consumer Portfolio Segment [Member] \| Mortgage Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net	8,009	6,413
Held For Investment Mortgage Finance Receivables Interest Only Mortgage Loans	$ 38	44
Consumer Portfolio Segment [Member] \| Mortgage Finance [Member] \| Six months or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	5.00%
Consumer Portfolio Segment [Member] \| Mortgage Finance [Member] \| One year six months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	2.00%
Consumer Portfolio Segment [Member] \| Mortgage Finance [Member] \| Two years six months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	0.00%
Consumer Portfolio Segment [Member] \| Mortgage Finance [Member] \| Three years six months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	38.00%
Consumer Portfolio Segment [Member] \| Mortgage Finance [Member] \| Four years six months, or greater [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	38.00%
Consumer Portfolio Segment [Member] \| Mortgage - Legacy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net	$ 3,075	3,360
Held For Investment Mortgage Finance Receivables Interest Only Mortgage Loans	$ 830	941
Consumer Portfolio Segment [Member] \| Mortgage - Legacy [Member] \| Six months or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	22.00%
Consumer Portfolio Segment [Member] \| Mortgage - Legacy [Member] \| One year six months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	22.00%
Consumer Portfolio Segment [Member] \| Mortgage - Legacy [Member] \| Two years six months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	2.00%
Consumer Portfolio Segment [Member] \| Mortgage - Legacy [Member] \| Three years six months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	0.00%
Consumer Portfolio Segment [Member] \| Mortgage - Legacy [Member] \| Four years six months, or greater [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	1.00%
Commercial Portfolio Segment [Member] \| Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net	$ 38,288	37,535	$ 35,175
Commercial Portfolio Segment [Member] \| Commercial And Industrial Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net	31,640	31,469
Commercial Portfolio Segment [Member] \| Commercial And Industrial Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net	3,037	2,640
Commercial Portfolio Segment [Member] \| Commercial Real Estate Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables and loans, net	$ 3,611	$ 3,426