Long-Term Debt (Pledged Assets Related to Secured Borrowings And Repurchase Agreement) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 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	$ 584	$ 2,864
Pledged Assets, Mortgage assets held for investment	7,708	8,524
Pledged Assets, Investment in operating leases	4,925	5,810
Pledged Assets, Not Separately Reported, Other	0	563
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	66,252	71,957
Secured Debt	45,127	47,594
Short-term borrowings	5,255	8,545
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	584	2,864
Pledged Assets, Mortgage assets held for investment	7,708	8,524
Pledged Assets, Investment in operating leases	3,967	3,190
Pledged Assets, Not Separately Reported, Other	0	0
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	43,076	48,159
Secured Debt	24,420	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	3,300	3,200
Secured Debt [Member]
Pledged Assets related to secured borrowings [Line Items]
Short-term borrowings	1,879	5,320
Consumer Loans Auto Financing Receivable [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	33,749	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	12,047	12,332
Commercial Automobile [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	19,286	21,249
Commercial Automobile [Member] | Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	$ 18,770	$ 21,249