Regulatory Capital (Schedule Of Regulatory Capital Amount And Ratios) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Leverage To Average Assets For Ally Bank	15.00%
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (to risk-weighted assets), Amount	$ 16,389	$ 15,165
Tier 1 (to risk-weighted assets), Ratio	12.55%	11.79%
Tier 1 (to risk-weighted assets), Required minimum	4.00%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Total (to risk-weighted assets), Amount	17,294	16,405
Total (to risk-weighted assets), Ratio	13.24%	12.76%
Total (to risk-weighted assets), Required minimum	8.00%
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%
Tier 1 leverage (to adjusted average assets), Amount	16,389	15,165
Tier One Leverage Capital to Average Assets	10.94%	10.23%
Tier 1 common (to risk-weighted assets), Amount	12,588	11,366
Tier 1 common (to risk-weighted assets), Ratio	9.64%	8.84%
Parent Company [Member] \| Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	3.00%
Parent Company [Member] \| Maximum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%
Ally Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (to risk-weighted assets), Amount	16,022	15,159
Tier 1 (to risk-weighted assets), Ratio	16.89%	16.73%
Tier 1 (to risk-weighted assets), Required minimum	4.00%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Total (to risk-weighted assets), Amount	16,468	15,809
Total (to risk-weighted assets), Ratio	17.36%	17.45%
Total (to risk-weighted assets), Required minimum	8.00%
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%
Tier 1 leverage (to adjusted average assets), Amount	16,022	15,159
Tier One Leverage Capital to Average Assets	15.44%	15.77%
Tier 1 Leverage To Average Assets For Ally Bank	15.00%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%
Tier 1 common (to risk-weighted assets), Amount	$ 16,022	$ 15,159
Tier 1 common (to risk-weighted assets), Ratio	16.89%	16.73%
Basel I [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (to risk-weighted assets), Required minimum	4.00%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Total (to risk-weighted assets), Required minimum	8.00%
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%
Basel I [Member] \| Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	3.00%
Basel I [Member] \| Maximum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%

Percentage Of Tier One Common Risk Based Capital to Risk Weighted Assets

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets in accordance with CLMA requirements for Ally Bank.

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Tier One Common Risk Based Capital

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- Definition

The amount of total capital as defined in the regulations.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Total Capital divided by risk weighted assets as defined in the regulations.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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