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Servicing Activities (Narrative - Automobile Servicing Activities) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Servicing Activities [Abstract]    
Automobile Servicing Fees $ 10ally_AutomobileServicingFees $ 9ally_AutomobileServicingFees