Fair Value (Fair Value of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale, net	$ 1,559us-gaap_LoansReceivableHeldForSaleNet	$ 2,003us-gaap_LoansReceivableHeldForSaleNet
Total finance receivables and loans, net	98,924	98,971
Nonmarketable equity securities	213ally_NonMarketableEquitySecurities	271ally_NonMarketableEquitySecurities
Deposit liabilities	60,875us-gaap_Deposits	58,222us-gaap_Deposits
Short-term borrowings	6,447us-gaap_ShortTermBorrowings	7,062us-gaap_ShortTermBorrowings
Long-term debt	65,760us-gaap_LongTermDebt	66,558us-gaap_LongTermDebt
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale, net	0	0
Total finance receivables and loans, net	0	0
Nonmarketable equity securities	0	0
Deposit liabilities	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale, net	0	485
Total finance receivables and loans, net	0	0
Nonmarketable equity securities	188	246
Deposit liabilities	0	0
Short-term borrowings	0	0
Long-term debt	24,376	25,224
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale, net	1,561	1,554
Total finance receivables and loans, net	99,781	99,430
Nonmarketable equity securities	32	33
Deposit liabilities	61,504	58,777
Short-term borrowings	6,447	7,063
Long-term debt	43,889	44,084
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale, net	1,559	2,003
Total finance receivables and loans, net	98,924	98,971
Nonmarketable equity securities	213	271
Deposit liabilities	60,875	58,222
Short-term borrowings	6,447	7,062
Long-term debt	65,760	66,558
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale, net	1,561	2,039
Total finance receivables and loans, net	99,781	99,430
Nonmarketable equity securities	220	279
Deposit liabilities	61,504	58,777
Short-term borrowings	6,447	7,063
Long-term debt	$ 68,265	$ 69,308

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- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

+ References

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Amount classified as loans attributable to disposal group held for sale or disposed of. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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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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