Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies	6 Months Ended
	Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies	Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies Ally Financial Inc. (together with its consolidated subsidiaries unless the context otherwise requires, Ally, the Company, we, us, or our) is a digital financial-services company committed to its promise to “Do It Right” for its consumer, commercial, and corporate customers. Ally is composed of an industry-leading independent automotive finance and insurance operation, an award-winning digital direct bank (Ally Bank, Member FDIC and Equal Housing Lender, which offers mortgage lending, point-of-sale personal lending, and a variety of deposit and other banking products), a corporate finance business for equity sponsors and middle-market companies, and securities brokerage and investment advisory services. A relentless ally for all things money, Ally helps people save well and earn well, so they can spend for what matters. We are a Delaware corporation and are registered as a BHC under the BHC Act, and an FHC under the GLB Act. Our accounting and reporting policies conform to U.S. GAAP. Additionally, where applicable, the policies conform to the accounting and reporting guidelines prescribed by bank regulatory authorities. Certain reclassifications may have been made to the prior periods’ financial statements and notes to conform to the current period’s presentation, which did not have a material impact on our Condensed Consolidated Financial Statements. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and that affect income and expenses during the reporting period and related disclosures. In developing the estimates and assumptions, management uses all available evidence; however, actual results could differ because of uncertainties associated with estimating the amounts, timing, and likelihood of possible outcomes. Our most significant estimates pertain to the allowance for loan losses, valuations of automotive lease assets and residuals, fair value of financial instruments, and the determination of the provision for income taxes. The Condensed Consolidated Financial Statements at June 30, 2021, and for the three months and six months ended June 30, 2021, and 2020, are unaudited but reflect all adjustments that are, in management’s opinion, necessary for the fair presentation of the results for the interim periods presented. All such adjustments are of a normal recurring nature. These unaudited Condensed Consolidated Financial Statements should be read in conjunction with the audited Consolidated Financial Statements (and the related Notes) included in our Annual Report on Form 10-K for the year ended December 31, 2020, as filed on February 24, 2021, with the SEC. Significant Accounting Policies Income Taxes In calculating the provision for interim income taxes, in accordance with ASC 740, Income Taxes, we apply an estimated annual effective tax rate to year-to-date ordinary income. At the end of each interim period, we estimate the effective tax rate expected to be applicable for the full fiscal year. This method differs from that described in Note 1 to the Consolidated Financial Statements in our 2020 Annual Report on Form 10-K, which describes our annual significant income tax accounting policy and related methodology. Refer to Note 1 to the Consolidated Financial Statements in our 2020 Annual Report on Form 10-K regarding additional significant accounting policies. Recently Adopted Accounting Standards Reference Rate Reform (ASU 2021-01) In January 2021, the FASB issued ASU 2021-01, Reference Rate Reform (Topic 848): Scope, which clarified the scope of ASU 2020-04, Reference Rate Reform: Facilitation of the Effects of Reference Rate Reform on Financial Reporting, indicating that certain optional expedients and exceptions included in ASU 2020-04 are applicable to derivative instruments affected by the market-wide change in interest rates used for discounting, margining, or contract price alignment. We adopted the amendments in this ASU immediately upon issuance in January 2021 on a prospective basis and will apply this guidance, along with the guidance from ASU 2020-04, as contracts are modified through December 2022. The adoption did not have an immediate direct impact on our financial statements. We do not expect there to be a material impact to our financial statements.