Regulatory Capital (Schedule Of Regulatory Capital Amount And Ratios) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Risk-based Capital required to be well capitalized to risk-weighted assets	4.50%
Tier 1 (to risk-weighted assets), Required minimum	6.00%
Total (to risk-weighted assets), Required minimum	8.00%
Common equity Tier 1 capital conservation buffer	2.50%
assets greater than $50 billion	$ 50,000
Series G Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred Stock Redemption, Aggregate Liquidation Preference	1,288
Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred Stock Repurchase, Aggregate Liquidation Preference	$ 325
Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Percentage Of Tier One Common Risk Based Capital to Risk Weighted Assets	5.00%
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (to risk-weighted assets), Required minimum	6.00%
Total (to risk-weighted assets), Required minimum	8.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%
Common Equity Tier 1 Capital	$ 13,181	$ 12,588
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets	9.83%	9.64%
Common Equity Tier 1 Capital Required for Capital Adequacy to Risk-weighted Assets	4.50%
Tier 1 (to risk-weighted assets), Amount	$ 15,734	$ 16,389
Tier 1 (to risk-weighted assets), Ratio	11.74%	12.55%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Total (to risk-weighted assets), Amount	$ 16,926	$ 17,294
Total (to risk-weighted assets), Ratio	12.63%	13.24%
Total (to risk-weighted assets), Well-capitalized minimum	10.00%
Tier 1 leverage (to adjusted average assets), Amount	$ 15,734	$ 16,389
Tier 1 leverage (to adjusted average assets), Ratio	10.35%	10.94%
Ally Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (to risk-weighted assets), Required minimum	6.00%
Total (to risk-weighted assets), Required minimum	8.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	15.00%
Common Equity Tier 1 Capital	$ 16,055	$ 16,022
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets	17.32%	16.89%
Common Equity Tier 1 Capital Required for Capital Adequacy to Risk-weighted Assets	4.50%
Common Equity Tier 1 Capital Required to be Well Capitalized to Risk-weighted Assets	6.50%
Tier 1 (to risk-weighted assets), Amount	$ 16,055	$ 16,022
Tier 1 (to risk-weighted assets), Ratio	17.32%	16.89%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%
Total (to risk-weighted assets), Amount	$ 16,448	$ 16,468
Total (to risk-weighted assets), Ratio	17.74%	17.36%
Total (to risk-weighted assets), Well-capitalized minimum	10.00%
Tier 1 leverage (to adjusted average assets), Amount	$ 16,055	$ 16,022
Tier 1 leverage (to adjusted average assets), Ratio	15.42%	15.44%
Tier 1 leverage (to adjusted average assets), Well-capitalized minimum	5.00%