Regulatory Capital (Schedule Of Regulatory Capital Amount And Ratios) (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Minimum [Member]	Sep. 30, 2012 Maximum [Member]	Sep. 30, 2012 Parent Company [Member]	Dec. 31, 2011 Parent Company [Member]	Sep. 30, 2012 Ally Bank [Member]	Dec. 31, 2011 Ally Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital Required for Capital Adequacy to Average Assets		3.00%	4.00%
Tier 1 Leverage To Average Assets For Ally Bank						15.00%
Tier 1 (to risk-weighted assets), Amount				$ 20,503,000,000	$ 21,158,000,000	$ 13,812,000,000	$ 12,953,000,000
Tier 1 (to risk-weighted assets), Ratio				13.64%	13.71%	16.98%	17.42%
Tier 1 (to risk-weighted assets), Required minimum				4.00%		4.00%
Tier 1 (to risk-weighted assets), Well-capitalized minimum				6.00%		6.00%
Total (to risk-weighted assets), Amount				21,994,000,000	22,755,000,000	14,640,000,000	13,675,000,000
Total (to risk-weighted assets), Ratio				14.63%	14.75%	18.00%	18.40%
Total (to risk-weighted assets), Required minimum				8.00%		8.00%
Total (to risk-weighted assets), Well-capitalized minimum				10.00%		10.00%
Tier 1 leverage (to adjusted average assets), Amount				20,503,000,000	21,158,000,000	13,812,000,000	12,953,000,000
Tier 1 leverage (to adjusted average assets), Ratio				11.29%	11.50%	15.47%	15.50%
Tier 1 leverage (to adjusted average assets), Well-capitalized minimum						5.00%
assets greater than $50 billion	50,000,000,000
Tier 1 common ration above 5 percent	5.00%
Tier 1 common (to risk-weighted assets), Amount				$ 11,020,000,000	$ 11,676,000,000
Tier 1 common (to risk-weighted assets), Ratio				7.33%	7.57%