Fair Value (Fair Value Option Election) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term Debt, Fair Value	$ 0	$ (830)
Fair Value Option Election, Unpaid Principal Balance [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	2,416	3,766
Consumer mortgage finance receivables and loans, net	0	2,436
Fair Value Option Election, Unpaid Principal Balance [Member] \| Mortgage Loans Held For Sale, Net [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status	47	54
Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due	36	53
Fair Value Option Election, Unpaid Principal Balance [Member] \| Consumer Mortgage Finance Receivables And Loans, Net [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status	0	506
Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due	0	362
Fair Value Option Election, Unpaid Principal Balance [Member] \| On-Balance Sheet Securitization Debt [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term Debt, Fair Value	0	(2,559)
Fair Value Option Election, Unpaid Principal Balance [Member] \| Loan repurchase liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Other Liabilities, Fair Value Disclosure	0	(57)
Fair Value Option Election, Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	2,490	3,919
Consumer mortgage finance receivables and loans, net	0	835
Fair Value Option Election, Fair Value [Member] \| Mortgage Loans Held For Sale, Net [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status	25	27
Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due	19	27
Fair Value Option Election, Fair Value [Member] \| Consumer Mortgage Finance Receivables And Loans, Net [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status	0	209
Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due	0	163
Fair Value Option Election, Fair Value [Member] \| On-Balance Sheet Securitization Debt [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term Debt, Fair Value	0	(830)
Fair Value Option Election, Fair Value [Member] \| Loan repurchase liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Other Liabilities, Fair Value Disclosure	$ 0	$ (29)

Consumer mortgage finance receivables and loans, net

No definition available.

Name:	gjm_ConsumerMortgageFinanceReceivablesAndLoansNetFairValueDisclosure
Namespace Prefix:	gjm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the aggregate fair value of loans held as assets that are 90 days or more past due for which the fair value option has been elected.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 28

-Subparagraph (e)(1)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 159

-Paragraph 18

-Subparagraph e(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the aggregate fair value of loans held as assets that are in nonaccrual status for which the fair value option has been elected, if the entity's policy is to recognize interest income separately from other changes in fair value.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 28

-Subparagraph (e)(2)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 159

-Paragraph 18

-Subparagraph e(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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

- Details

Name:	us-gaap_FairValueOptionQuantitativeDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents mortgage loans held-for-sale as presented on the statement of financial position which are due the Company as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This element represents the fair value of liabilities categorized as other which are not in and of themselves material enough to require separate disclosure.

+ References

No definition available.

+ Details

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