Debt (Narrative - Trust Preferred Securities) (Details) - USD ($) $ / shares in Units, $ in Billions	Jun. 30, 2019	Dec. 31, 2018
Narrative - Trust Preferred Securities [Line Items]
Trust preferred securities	$ 2.6	$ 2.6
Trust preferred securities, fixed rate, floating rate, percentage	8.125%
Preferred stock, liquidation amount per share	$ 25
Distribution payable in addition to annual rate equal to three-month London interbank offer rate, percentage	5.785%
Period of consecutive quarters for which Ally has right to defer interest payments, maximum	20
Redemption price, percentage of principal debt, plus accrued and unpaid interest	100.00%
Fixed income interest rate
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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- Definition

Distributions will be payable at an annual rate equal to three-month London interbank offer rate plus:

+ References

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- Definition

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

+ References

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- Definition

Percent of principal debt, plus accrued and unpaid interest is the redemption price if Ally redeems the Series 2 TRUPS at anytime on or before February 15, 2040.

+ References

No definition available.

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- Definition

Trust preferred securities

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No definition available.

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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- Definition

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
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-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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-Section S99
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-Subparagraph (SX 210.4-08(d)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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