Regulatory Capital (Schedule Of Regulatory Capital Amount And Ratios) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Apr. 23, 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%
Total (to risk-weighted assets), Required minimum		8.00%
Common equity Tier 1 capital conservation buffer		2.50%
Tier 1 (to risk-weighted assets), Well-capitalized minimum		6.00%
assets greater than $50 billion		$ 50,000,000,000
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		14,240,000,000	12,588,000,000
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets		10.94%	9.64%
Common Equity Tier 1 Capital Required for Capital Adequacy to Risk-weighted Assets		4.50%
Tier 1 (to risk-weighted assets), Amount		17,131,000,000	16,389,000,000
Tier 1 (to risk-weighted assets), Ratio		13.16%	12.55%
Total (to risk-weighted assets), Amount		18,365,000,000	17,294,000,000
Total (to risk-weighted assets), Ratio		14.11%	13.24%
Tier 1 leverage (to adjusted average assets), Amount		17,131,000,000	16,389,000,000
Tier 1 leverage (to adjusted average assets), Ratio		11.43%	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		16,185,000,000	16,022,000,000
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets		17.49%	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		16,185,000,000	16,022,000,000
Tier 1 (to risk-weighted assets), Ratio		17.49%	16.89%
Tier 1 (to risk-weighted assets), Well-capitalized minimum		8.00%
Total (to risk-weighted assets), Amount		16,574,000,000	16,468,000,000
Total (to risk-weighted assets), Ratio		17.91%	17.36%
Total (to risk-weighted assets), Well-capitalized minimum		10.00%
Tier 1 leverage (to adjusted average assets), Amount		16,185,000,000	16,022,000,000
Tier 1 leverage (to adjusted average assets), Ratio		15.61%	15.44%
Tier 1 leverage (to adjusted average assets), Well-capitalized minimum		5.00%
Series G Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Payments for Repurchase of Redeemable Preferred Stock	$ 1,300,000,000
Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased				13
Stock Repurchase Program, Repurchase Price per Share				$ 26.65
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%