Regulatory Capital (Schedule Of Regulatory Capital Amount And Ratios) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
assets greater than $50 billion	$ 50,000,000,000
Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 common (to risk-weighted assets), Ratio	5.00%
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (to risk-weighted assets), Amount	16,227,000,000	15,165,000,000
Tier 1 (to risk-weighted assets), Ratio	12.65%	11.79%
Tier 1 (to risk-weighted assets), Required minimum	4.00%
Tier 1 (to risk-weighted assets), Well-capitalized minimum	6.00%
Total (to risk-weighted assets), Amount	17,275,000,000	16,405,000,000
Total (to risk-weighted assets), Ratio	13.47%	12.76%
Total (to risk-weighted assets), Required minimum	8.00%
Total (to risk-weighted assets), Well-capitalized minimum	10.00%
Tier 1 leverage (to adjusted average assets), Amount	16,227,000,000	15,165,000,000
Tier 1 leverage (to adjusted average assets), Ratio	10.91%	10.23%
Tier 1 common (to risk-weighted assets), Amount	12,427,000,000	11,366,000,000
Tier 1 common (to risk-weighted assets), Ratio	9.69%	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	15,898,000,000	15,159,000,000
Tier 1 (to risk-weighted assets), Ratio	17.32%	16.73%
Tier 1 (to risk-weighted assets), Required minimum	4.00%
Tier 1 (to risk-weighted assets), Well-capitalized minimum	6.00%
Total (to risk-weighted assets), Amount	16,493,000,000	15,809,000,000
Total (to risk-weighted assets), Ratio	17.97%	17.45%
Total (to risk-weighted assets), Required minimum	8.00%
Total (to risk-weighted assets), Well-capitalized minimum	10.00%
Tier 1 leverage (to adjusted average assets), Amount	15,898,000,000	15,159,000,000
Tier 1 leverage (to adjusted average assets), Ratio	15.71%	15.77%
Tier 1 Leverage To Average Assets For Ally Bank	15.00%
Tier 1 leverage (to adjusted average assets), Well-capitalized minimum	5.00%
Tier 1 common (to risk-weighted assets), Amount	$ 15,898,000,000	$ 15,159,000,000
Tier 1 common (to risk-weighted assets), Ratio	17.32%	16.73%