Long-Term Debt (Pledged Assets Related to Secured Borrowings And Repurchase Agreement) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Pledged Assets related to secured borrowings [Line Items]
Trading Securities Pledged as Collateral	$ 0	$ 27
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	401	780
Pledged Financial Instruments, Not Separately Reported, Loans Receivable Pledged as Collateral	0	805
Pledged Assets, Mortgage assets held for investment	10,025	12,197
Pledged Assets, Investment in operating leases	5,909	4,555
Pledged Assets, Mortgage servicing rights	902	1,920
Pledged Assets, Not Separately Reported, Other	2,719	3,973
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	78,154	78,500
Secured Debt	52,525	52,965
Short-term borrowings	5,877	7,680
Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Trading Securities Pledged as Collateral	0	0
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	401	780
Pledged Financial Instruments, Not Separately Reported, Loans Receivable Pledged as Collateral	0	0
Pledged Assets, Mortgage assets held for investment	10,025	11,188
Pledged Assets, Investment in operating leases	1,818	431
Pledged Assets, Mortgage servicing rights	902	1,286
Pledged Assets, Not Separately Reported, Other	2,068	1,816
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	48,800	47,702
Secured Debt	27,882	25,533
Pledged assets for Federal Home Loan Bank and 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	9,300	11,800
Pledged assets for Federal Home Loan Bank under blanket-lien [Member] | Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	8,400	7,300
Secured Debt [Member]
Pledged Assets related to secured borrowings [Line Items]
Short-term borrowings	1,914	3,165
Consumer Portfolio Segment [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	36,488	33,888
Consumer Portfolio Segment [Member] | Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	16,970	17,320
Commercial Portfolio Segment [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	21,710	20,355
Commercial Portfolio Segment [Member] | Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	$ 16,616	$ 14,881