Long-Term Debt (Pledged Assets Related to Secured Borrowings And Repurchase Agreement) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Pledged Assets related to secured borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	$ 786	$ 2,864
Pledged Assets, Mortgage assets held for investment	7,541	8,524
Pledged Assets, Investment in operating leases	6,820	5,810
Pledged Assets, Not Separately Reported, Other	0	563
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	69,190	71,957
Secured Debt	47,867us-gaap_SecuredDebt	47,594us-gaap_SecuredDebt
Short-term borrowings	7,062us-gaap_ShortTermBorrowings	8,545us-gaap_ShortTermBorrowings
Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	786	2,864
Pledged Assets, Mortgage assets held for investment	7,541	8,524
Pledged Assets, Investment in operating leases	4,672	3,190
Pledged Assets, Not Separately Reported, Other	0	0
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	44,345	48,159
Secured Debt	27,134	27,818
Pledged assets for Federal Home Loan Bank [Member] \| Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	10,700	12,700
Pledged assets for Federal Reserve Bank [Member] \| Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	3,200	3,200
Secured Debt [Member]
Pledged Assets related to secured borrowings [Line Items]
Short-term borrowings	3,724	5,320
Consumer Loans Auto Financing Receivable [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	33,438	32,947
Consumer Loans Auto Financing Receivable [Member] \| Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	11,263	12,332
Commercial Automobile [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	20,605	21,249
Commercial Automobile [Member] \| Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	$ 20,083	$ 21,249

Pledged Assets, Investment in operating leases

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- Definition

Pledged Assets, Mortgage assets held for investment

+ References

No definition available.

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- Definition

The carrying amount, as of the date of the latest financial statement presented, of finance receivables which are owned but transferred to serve as collateral for the payment of the related debt obligation, primarily a secured borrowing or repurchase agreement, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)

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- Definition

The carrying amount, as of the date of the latest financial statement presented, of all assets that are pledged as collateral for the payment of the related debt obligation primarily arising from secured borrowings, repurchase agreements or other current or potential obligations, where the secured party does not have the right by contract or custom to sell or re-pledge the collateral and therefore are not reclassified and separately reported in the statement of financial position.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

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- Definition

The carrying amount, as of the date of the latest financial statement presented, of other assets which are owned but transferred to serve as collateral for the payment of the related debt obligation, primarily a secured borrowing or repurchase agreement, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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-Paragraph 1A

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- Definition

The carrying amount as of the date of the latest financial statement presented of other securities classified as available for sale or held for investment which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

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-Name Accounting Standards Codification

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-Section 50

-Paragraph 1A

-Subparagraph (b)(1)(i)

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- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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-Article 9

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-Name Regulation S-X (SX)

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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-Subparagraph a

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-Subparagraph (SX 210.9-03.13)

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-Number 210

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-Subparagraph 2, 3

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