Long-Term Debt (Pledged Assets Related to Secured Borrowings And Repurchase Agreement) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Pledged Assets related to secured borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	$ 500	$ 1,911
Pledged Assets, Mortgage assets held for investment	9,715	9,866
Pledged Assets, Investment in operating leases	6,872	6,058
Pledged Assets, Not Separately Reported, Other	973	999
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	60,587	67,997
Secured Debt	38,790	45,111
Short-term borrowings	7,618	7,461
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	500	1,911
Pledged Assets, Mortgage assets held for investment	9,715	9,866
Pledged Assets, Investment in operating leases	2,966	1,691
Pledged Assets, Not Separately Reported, Other	252	272
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	44,680	48,179
Secured Debt	25,864	29,162
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	12,500	12,600
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	3,100	1,900
Secured Debt [Member]
Pledged Assets related to secured borrowings [Line Items]
Short-term borrowings	4,382	4,200
Consumer Loans Auto Financing Receivable [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	23,953	29,557
Consumer Loans Auto Financing Receivable [Member] \| Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	12,673	14,833
Commercial Automobile [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	18,574	19,606
Commercial Automobile [Member] \| Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	$ 18,574	$ 19,606

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.

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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.

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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.

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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.

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