Contingencies and Other Risks	12 Months Ended
Dec. 31, 2018
Loss Contingency [Abstract]
Contingencies Disclosure	Contingencies and Other Risks Concentration with GM and Chrysler While we are continuing to diversify our automotive finance and insurance businesses and to expand into other financial services, General Motors Company (GM) and Fiat Chrysler Automobiles US LLC (Chrysler) dealers and their retail customers continue to constitute a significant portion of our customer base. GM, Chrysler, and their captive finance companies compete vigorously with us and could take further actions that negatively impact the amount of business that we do with GM and Chrysler dealers and their customers. Further, a significant adverse change in GM’s or Chrysler’s business—including, for example, in the production or sale of GM or Chrysler vehicles, the quality or resale value of GM or Chrysler vehicles, GM’s or Chrysler’s relationships with its key suppliers, or the rate or volume of recalls of GM or Chrysler vehicles—could negatively impact our GM and Chrysler dealer and retail customer bases and the value of collateral securing our extensions of credit to them. Any future reductions in GM and Chrysler business that we are not able to offset could adversely affect our business and financial results. Legal Matters Ally and its subsidiaries, including Ally Bank, are or may be subject to potential liability in connection with pending or threatened legal proceedings and other matters. These legal matters may be formal or informal and include litigation and arbitration with one or more identified claimants, certified or purported class actions with yet-to-be-identified claimants, and regulatory or other governmental information-gathering requests, examinations, investigations, and enforcement proceedings. Our legal matters exist in varying stages of adjudication, arbitration, negotiation, or investigation and span our business lines and operations. Claims may be based in law or equity—such as those arising under contracts or in tort and those involving banking, consumer-protection, securities, tax, employment, and other laws—and some can present novel legal theories and allege substantial or indeterminate damages. We accrue for a legal matter when a loss becomes probable and the amount of loss can be reasonably estimated. Accruals are evaluated each quarter and may be adjusted, upward or downward, based on our best judgment after consultation with counsel. No assurance exists that our accruals will not need to be adjusted in the future. When a probable or reasonably possible loss on a legal matter could be material to our consolidated financial condition, results of operations, or cash flows, we provide disclosure in this note as prescribed by ASC 450, Contingencies. The course and outcome of legal matters are inherently unpredictable. This is especially so when a matter is still in its early stages, the damages sought are indeterminate or unsupported, significant facts are unclear or disputed, novel questions of law or other meaningful legal uncertainties exist, a request to certify a proceeding as a class action is outstanding or granted, multiple parties are named, or regulatory or other governmental entities are involved. As a result, we often are unable to determine how or when threatened or pending legal matters will be resolved and what losses may be incurred. Actual losses may be higher or lower than any amounts accrued or estimated for those matters, possibly to a significant degree. Descriptions of our material legal matters follow. We do not believe, however, that an estimate of reasonably possible losses or a range of reasonably possible losses—whether in excess of any related accrual or where no accrual exists—can be made for any of these matters for some or all of the reasons identified in the preceding paragraph. Securities Litigation In October 2016, a purported class action—Bucks County Employees Retirement Fund v. Ally Financial Inc. et al.—was filed in the Circuit Court for Wayne County in the State of Michigan (Case No. 16-013616-CZ). The complaint alleged material misstatements and omissions in connection with Ally’s initial public offering in April 2014, including a failure to adequately disclose the severity of rising subprime automotive loan delinquency rates, deficient underwriting measures employed in the origination of subprime automotive loans, and aggressive tactics used with low-income borrowers. The request for relief included an indeterminate amount of damages, fees, and costs and other remedies. In January 2017, another purported class action—National Shopmen Pension Fund v. Ally Financial Inc. et al.—was filed in the Circuit Court for Oakland County in the State of Michigan (Case No. 2017-156719-CB). In March 2017, a third purported class action—James McIntire v. Ally Financial Inc. et al.—was filed in the Circuit Court for Wayne County in the State of Michigan (Case No. 17-003811-CZ). The allegations and requested relief in the National Shopmen Pension Fund and James McIntire complaints were substantially similar to those included in the complaint filed by Bucks County Employees Retirement Fund. All three matters were initially removed to the U.S. District Court for the Eastern District of Michigan, were then remanded back to the state circuit courts, and were consolidated for discovery in Wayne County Circuit Court as In re Ally Financial, Inc. Securities Litigation (Case No. 16-013616-CB). In November 2017, the plaintiffs filed a consolidated amended complaint. In January 2019, the Wayne County Circuit Court entered an order granting a motion by the defendants to dismiss the complaint. The order was not appealed, and the case has been closed. Other Contingencies Ally and its subsidiaries, including Ally Bank, are or may be subject to potential liability under various other contingent exposures, including indemnification, tax, self-insurance, and other miscellaneous contingencies. We accrue for a contingent exposure when a loss becomes probable and the amount of loss can be reasonably estimated. Accruals are evaluated each quarter and may be adjusted, upward or downward, based on our best judgment. No assurance exists that our accruals will not need to be adjusted in the future, and actual losses may be higher or lower than any amounts accrued or estimated for those exposures, possibly to a significant degree. On the basis of information currently available, we do not believe that these other contingent exposures will be material to our consolidated financial condition, results of operations, or cash flows. Refer to Note 1 for additional information related to our policy for establishing reserves for legal and regulatory matters.

Contingencies and Other Risks

Concentration with GM and Chrysler

While we are continuing to diversify our automotive finance and insurance businesses and to expand into other financial services, General Motors Company (GM) and Fiat Chrysler Automobiles US LLC (Chrysler) dealers and their retail customers continue to constitute a significant portion of our customer base. GM, Chrysler, and their captive finance companies compete vigorously with us and could take further actions that negatively impact the amount of business that we do with GM and Chrysler dealers and their customers. Further, a significant adverse change in GM’s or Chrysler’s business—including, for example, in the production or sale of GM or Chrysler vehicles, the quality or resale value of GM or Chrysler vehicles, GM’s or Chrysler’s relationships with its key suppliers, or the rate or volume of recalls of GM or Chrysler vehicles—could negatively impact our GM and Chrysler dealer and retail customer bases and the value of collateral securing our extensions of credit to them. Any future reductions in GM and Chrysler business that we are not able to offset could adversely affect our business and financial results.

Legal Matters

Ally and its subsidiaries, including Ally Bank, are or may be subject to potential liability in connection with pending or threatened legal proceedings and other matters. These legal matters may be formal or informal and include litigation and arbitration with one or more identified claimants, certified or purported class actions with yet-to-be-identified claimants, and regulatory or other governmental information-gathering requests, examinations, investigations, and enforcement proceedings. Our legal matters exist in varying stages of adjudication, arbitration, negotiation, or investigation and span our business lines and operations. Claims may be based in law or equity—such as those arising under contracts or in tort and those involving banking, consumer-protection, securities, tax, employment, and other laws—and some can present novel legal theories and allege substantial or indeterminate damages.

We accrue for a legal matter when a loss becomes probable and the amount of loss can be reasonably estimated. Accruals are evaluated each quarter and may be adjusted, upward or downward, based on our best judgment after consultation with counsel. No assurance exists that our accruals will not need to be adjusted in the future. When a probable or reasonably possible loss on a legal matter could be material to our consolidated financial condition, results of operations, or cash flows, we provide disclosure in this note as prescribed by ASC 450, Contingencies.

The course and outcome of legal matters are inherently unpredictable. This is especially so when a matter is still in its early stages, the damages sought are indeterminate or unsupported, significant facts are unclear or disputed, novel questions of law or other meaningful legal uncertainties exist, a request to certify a proceeding as a class action is outstanding or granted, multiple parties are named, or regulatory or other governmental entities are involved. As a result, we often are unable to determine how or when threatened or pending legal matters will be resolved and what losses may be incurred. Actual losses may be higher or lower than any amounts accrued or estimated for those matters, possibly to a significant degree.

Descriptions of our material legal matters follow. We do not believe, however, that an estimate of reasonably possible losses or a range of reasonably possible losses—whether in excess of any related accrual or where no accrual exists—can be made for any of these matters for some or all of the reasons identified in the preceding paragraph.

Securities Litigation

In October 2016, a purported class action—Bucks County Employees Retirement Fund v. Ally Financial Inc. et al.—was filed in the Circuit Court for Wayne County in the State of Michigan (Case No. 16-013616-CZ). The complaint alleged material misstatements and omissions in connection with Ally’s initial public offering in April 2014, including a failure to adequately disclose the severity of rising subprime automotive loan delinquency rates, deficient underwriting measures employed in the origination of subprime automotive loans, and aggressive tactics used with low-income borrowers. The request for relief included an indeterminate amount of damages, fees, and costs and other remedies. In January 2017, another purported class action—National Shopmen Pension Fund v. Ally Financial Inc. et al.—was filed in the Circuit Court for Oakland County in the State of Michigan (Case No. 2017-156719-CB). In March 2017, a third purported class action—James McIntire v. Ally Financial Inc. et al.—was filed in the Circuit Court for Wayne County in the State of Michigan (Case No. 17-003811-CZ). The allegations and requested relief in the National Shopmen Pension Fund and James McIntire complaints were substantially similar to those included in the complaint filed by Bucks County Employees Retirement Fund. All three matters were initially removed to the U.S. District Court for the Eastern District of Michigan, were then remanded back to the state circuit courts, and were consolidated for discovery in Wayne County Circuit Court as In re Ally Financial, Inc. Securities Litigation (Case No. 16-013616-CB). In November 2017, the plaintiffs filed a consolidated amended complaint. In January 2019, the Wayne County Circuit Court entered an order granting a motion by the defendants to dismiss the complaint. The order was not appealed, and the case has been closed.

Other Contingencies

Ally and its subsidiaries, including Ally Bank, are or may be subject to potential liability under various other contingent exposures, including indemnification, tax, self-insurance, and other miscellaneous contingencies. We accrue for a contingent exposure when a loss becomes probable and the amount of loss can be reasonably estimated. Accruals are evaluated each quarter and may be adjusted, upward or downward, based on our best judgment. No assurance exists that our accruals will not need to be adjusted in the future, and actual losses may be higher or lower than any amounts accrued or estimated for those exposures, possibly to a significant degree. On the basis of information currently available, we do not believe that these other contingent exposures will be material to our consolidated financial condition, results of operations, or cash flows. Refer to Note 1 for additional information related to our policy for establishing reserves for legal and regulatory matters.