Regulatory Capital (Schedule Of Regulatory Capital Amount And Ratios) (Details) - USD ($) shares in Millions, $ in Millions	Mar. 31, 2016	Dec. 31, 2015
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
Federal Reserve Bank Stock	$ 435	$ 0
Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred Stock, Notice of Redemption	700
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred Stock, Notice of Redemption	500
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	$ 12,656	$ 12,507
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets	9.47%	9.21%
Common Equity Tier 1 Capital Required for Capital Adequacy to Risk-weighted Assets	4.50%
Tier 1 (to risk-weighted assets), Amount	$ 15,462	$ 15,077
Tier 1 (to risk-weighted assets), Ratio	11.57%	11.10%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Total (to risk-weighted assets), Amount	$ 17,363	$ 17,005
Total (to risk-weighted assets), Ratio	13.00%	12.52%
Total (to risk-weighted assets), Well-capitalized minimum	10.00%
Tier 1 leverage (to adjusted average assets), Amount	$ 15,462	$ 15,077
Tier 1 leverage (to adjusted average assets), Ratio	9.87%	9.73%
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	$ 16,871	$ 16,594
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets	17.61%	17.05%
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	$ 16,871	$ 16,594
Tier 1 (to risk-weighted assets), Ratio	17.61%	17.05%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%
Total (to risk-weighted assets), Amount	$ 17,344	$ 17,043
Total (to risk-weighted assets), Ratio	18.11%	17.51%
Total (to risk-weighted assets), Well-capitalized minimum	10.00%
Tier 1 leverage (to adjusted average assets), Amount	$ 16,871	$ 16,594
Tier 1 leverage (to adjusted average assets), Ratio	15.25%	15.38%
Tier 1 leverage (to adjusted average assets), Well-capitalized minimum	5.00%