Contingencies and Other Risks	6 Months Ended
Jun. 30, 2018
Loss Contingency [Abstract]
Contingencies Disclosure [Text Block]	Contingencies and Other Risks 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). This matter was removed to the U.S. District Court for the Eastern District of Michigan on November 18, 2016. The complaint alleges 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 includes 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). This matter was removed to the U.S. District Court for the Eastern District of Michigan on January 30, 2017. 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). This matter was removed to the U.S. District Court for the Eastern District of Michigan on March 15, 2017. The allegations and requested relief in the National Shopmen Pension Fund and James McIntire complaints are substantially similar to those included in the complaint filed by Bucks County Employees Retirement Fund. All three matters were remanded from the U.S. District Court for the Eastern District of Michigan to the state circuit courts on May 26, 2017, and have been 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 April 2018, the court entered a scheduling order setting deadlines for briefing of defendants’ joint motion for summary disposition. We intend to vigorously defend against each of these actions. Automotive Subprime Matters In October 2014, we received a document request from the SEC in connection with its investigation related to subprime automotive finance and related securitization activities. Separately, in December 2014, we received a subpoena from the U.S. Department of Justice requesting similar information. In May 2015 and December 2016, we received information requests from the New York Department of Financial Services requesting similar information. We responded timely to each of the requests. 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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for additional information related to our policy for establishing reserves for legal and regulatory matters.

Contingencies and Other Risks

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). This matter was removed to the U.S. District Court for the Eastern District of Michigan on November 18, 2016. The complaint alleges 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 includes 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). This matter was removed to the U.S. District Court for the Eastern District of Michigan on January 30, 2017. 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). This matter was removed to the U.S. District Court for the Eastern District of Michigan on March 15, 2017. The allegations and requested relief in the National Shopmen Pension Fund and James McIntire complaints are substantially similar to those included in the complaint filed by Bucks County Employees Retirement Fund. All three matters were remanded from the U.S. District Court for the Eastern District of Michigan to the state circuit courts on May 26, 2017, and have been 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 April 2018, the court entered a scheduling order setting deadlines for briefing of defendants’ joint motion for summary disposition. We intend to vigorously defend against each of these actions.

Automotive Subprime Matters

In October 2014, we received a document request from the SEC in connection with its investigation related to subprime automotive finance and related securitization activities. Separately, in December 2014, we received a subpoena from the U.S. Department of Justice requesting similar information. In May 2015 and December 2016, we received information requests from the New York Department of Financial Services requesting similar information. We responded timely to each of the requests.

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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for additional information related to our policy for establishing reserves for legal and regulatory matters.