Long-Term Debt (Pledged Assets Related to Secured Borrowings And Repurchase Agreement) (Details) (USD $) In Millions, unless otherwise specified	Jun. 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	$ 289	$ 2,864
Pledged Assets, Mortgage assets held for investment	7,958	8,524
Pledged Assets, Investment in operating leases	4,931	5,810
Pledged Assets, Not Separately Reported, Other	0	563
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	69,362	71,957
Secured Debt	47,761	47,594
Short-term borrowings	6,369	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	289	2,864
Pledged Assets, Mortgage assets held for investment	7,958	8,524
Pledged Assets, Investment in operating leases	3,614	3,190
Pledged Assets, Not Separately Reported, Other	0	0
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	45,134	48,159
Secured Debt	26,038	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	10,900	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	3,000	3,200
Secured Debt [Member]
Pledged Assets related to secured borrowings [Line Items]
Short-term borrowings	3,029	5,320
Consumer Loans Auto Financing Receivable [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	35,443	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	13,176	12,332
Commercial Automobile [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	20,741	21,249
Commercial Automobile [Member] | Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	$ 20,097	$ 21,249