Long-Term Debt Long-Term Debt (Narrative - Trust Preferred Securities) (Details) $ / shares in Units, $ in Billions	Jun. 30, 2016 USD ($) $ / shares
Narrative - Trust Preferred Securities [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	8.125%
Preferred Stock, Liquidation Preference Per Share \| $ / shares	$ 25
From and including February 15, 2016, to but excluding February 15, 2040, distributions will be payable at an annual rate equal to three-month London interbank offer rate plus:	5.785%
Ally has the right to defer payments of interest for a period not exceeding consecutive quarters of:	20
Percent of principle debt, plus accrued and unpaid interest is the redemption price if Ally redeems the Series 2 TRUPS on or after February 15, 2016.	100.00%
Fixed Income Interest Rate [Member]
Narrative - Trust Preferred Securities [Line Items]
Trust preferred securities \| $	$ 2.6

Ally has the right to defer payments of interest for a period not exceeding consecutive quarters of

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From and including February 15, 2016, to but excluding February 15, 2040, distributions will be payable at an annual rate equal to three-month London interbank offer rate plus:

+ References

No definition available.

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- Definition

[Line Items] for Narrative - Trust Preferred Securities [Table]

+ References

No definition available.

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Percent of principle debt, plus accrued and unpaid interest is the redemption price if Ally redeems the Series 2 TRUPS on or after February 15, 2016.

+ References

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- Definition

Trust preferred securities

+ References

No definition available.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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The per share liquidation preference (or restrictions) of nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(d)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29
-Article 5

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