Regulatory Capital (Schedule Of Regulatory Capital Amount And Ratios) (Details) - USD ($)	6 Months Ended
	Jun. 30, 2016	Mar. 21, 2016	Dec. 31, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Capital Required for Capital Adequacy 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%
Federal Reserve Bank Stock	$ 435,000,000	$ 435,000,000	$ 0
assets greater than $50 billion	50,000,000,000
Dividends	$ 0.08
Common Stock, Shares, Outstanding	483,753,360		481,980,111
Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred Stock, Notice of Redemption	700,000,000
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred Stock, Notice of Redemption	500,000,000
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Capital Required for Capital Adequacy 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%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%
Common Equity Tier 1 Capital	$ 12,829,000,000		$ 12,507,000,000
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets	9.59%		9.21%
Tier 1 (to risk-weighted assets), Amount	$ 14,959,000,000		$ 15,077,000,000
Tier 1 (to risk-weighted assets), Ratio	11.18%		11.10%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Total (to risk-weighted assets), Amount	$ 17,166,000,000		$ 17,005,000,000
Total (to risk-weighted assets), Ratio	12.83%		12.52%
Total (to risk-weighted assets), Well-capitalized minimum	10.00%
Tier 1 leverage (to adjusted average assets), Amount	$ 14,959,000,000		$ 15,077,000,000
Tier 1 leverage (to adjusted average assets), Ratio	9.63%		9.73%
Ally Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Capital Required for Capital Adequacy 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%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	15.00%
Common Equity Tier 1 Capital	$ 17,209,000,000		$ 16,594,000,000
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets	17.64%		17.05%
Common Equity Tier 1 Capital Required to be Well Capitalized to Risk-weighted Assets	6.50%
Tier 1 (to risk-weighted assets), Amount	$ 17,209,000,000		$ 16,594,000,000
Tier 1 (to risk-weighted assets), Ratio	17.64%		17.05%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%
Total (to risk-weighted assets), Amount	$ 17,712,000,000		$ 17,043,000,000
Total (to risk-weighted assets), Ratio	18.15%		17.51%
Total (to risk-weighted assets), Well-capitalized minimum	10.00%
Tier 1 leverage (to adjusted average assets), Amount	$ 17,209,000,000		$ 16,594,000,000
Tier 1 leverage (to adjusted average assets), Ratio	15.31%		15.38%
Tier 1 leverage (to adjusted average assets), Well-capitalized minimum	5.00%