Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies	9 Months Ended
Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block]	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, or we, us, or our) is a leading digital financial-services company. As a customer-centric company with passionate customer service and innovative financial solutions, we are relentlessly focused on “Doing It Right” and being a trusted financial-services provider to our consumer, commercial, and corporate customers. We are one of the largest full-service automotive finance operations in the country and offer a wide range of financial services and insurance products to dealerships and consumers. Our award-winning online bank (Ally Bank, Member Federal Deposit Insurance Corporation and Equal Housing Lender) offers mortgage-lending services and a variety of deposit and other banking products, including savings, money-market, and checking accounts, certificates of deposit (CDs), and individual retirement accounts (IRAs). Additionally, we offer securities-brokerage and investment-advisory services through Ally Invest. Our robust corporate finance business offers capital for equity sponsors and middle-market companies. We are a Delaware corporation and are registered as a bank holding company (BHC) under the Bank Holding Company Act of 1956, as amended, and a financial holding company (FHC) under the Gramm-Leach-Bliley Act of 1999, as amended. Our accounting and reporting policies conform to accounting principles generally accepted in the United States of America (GAAP). Additionally, where applicable, the policies conform to the accounting and reporting guidelines prescribed by bank regulatory authorities. 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 September 30, 2019, and for the three months and nine months ended September 30, 2019, and 2018, 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, 2018, as filed on February 20, 2019, with the U.S. Securities and Exchange Commission (SEC). Significant Accounting Policies Lease Accounting At contract inception, we determine whether the contract is or contains a lease based on the terms and conditions of the contract. Lease contracts are recognized on our Condensed Consolidated Balance Sheet as right-of-use (ROU) assets and lease liabilities; however, we have elected not to recognize ROU assets and lease liabilities on real estate leases with terms of one year or less. Lease liabilities and their corresponding ROU assets are recorded based on the present value of the future lease payments over the expected lease term. As the interest rate implicit in the lease contract is typically not readily determinable, we utilize our incremental borrowing rate, which is the rate we would incur to borrow on a collateralized basis over a similar term on an amount equal to the lease payments in a similar economic environment. The ROU asset also includes initial direct costs paid less lease incentives received from the lessor. Our lease contracts are generally classified as operating and, as a result, we recognize a single lease cost within other operating expenses on the income statement on a straight-line basis over the lease term. This update to our accounting policy resulted from our adoption of Accounting Standards Update (ASU) 2016-02 on January 1, 2019, as further described within the section below titled Recently Adopted Accounting Standards. Investments Premiums on debt securities that have noncontingent call features that are callable at fixed prices on preset dates are amortized to the earliest call date as an adjustment to investment yield. All other premiums and discounts on debt securities are amortized over the stated maturity of the security as an adjustment to investment yield. This method of amortization differs from that described in Note 1 to the Consolidated Financial Statements in our 2018 Annual Report on Form 10-K, which describes our full accounting policy for Investments. This update to our amortization methodology resulted from the adoption of ASU 2017-08 on January 1, 2019, as further described within the section below titled Recently Adopted Accounting Standards. Income Taxes In calculating the provision for interim income taxes, in accordance with Accounting Standards Codification (ASC) Topic 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 2018 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 2018 Annual Report on Form 10-K regarding additional significant accounting policies. Recently Adopted Accounting Standards Leases (ASU 2016-02) In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02. The amendments in this update primarily replaced the existing accounting requirements for operating leases for lessees. Lessee accounting requirements for finance leases (previously referred to as capital leases) and lessor accounting requirements for operating leases and sales type and direct financing leases were largely unchanged. The amendments require the lessee of an operating lease to record a balance sheet gross-up upon lease commencement by recognizing a ROU asset and lease liability equal to the present value of the lease payments. The ROU asset and lease liability should be derecognized in a manner that effectively yields a straight line lease expense over the lease term. In addition to the changes to the lessee operating lease accounting requirements, the amendments also changed the types of costs that can be capitalized related to a lease agreement for both lessees and lessors. The amendments also require additional disclosures for all lease types for both lessees and lessors. The FASB issued additional ASUs to clarify the guidance and provide certain practical expedients and an additional transition option. We adopted ASU 2016-02 and the subsequent ASUs that modified ASU 2016-02 (collectively, the amendments) on January 1, 2019. This includes the early adoption of ASU 2019-01, which was issued in March 2019 to amend certain provisions included in ASU 2016-02. We adopted this guidance using the modified retrospective approach on January 1, 2019, and have not adjusted prior period comparative information and will continue to disclose prior period financial information in accordance with the previous lease accounting guidance. We have elected certain practical expedients permitted within the amendments that allowed us to not reassess (i) current lease classifications, (ii) whether existing contracts meet the definition of a lease under the amendments to the lease guidance, and (iii) whether current initial direct costs meet the new criteria for capitalization, for all existing leases as of the adoption date. We made an accounting policy election to calculate the impact of adoption using the remaining minimum lease payments and remaining lease term for each contract that was identified as a lease, discounted at our incremental borrowing rate as of the adoption date. The adoption of the amendments resulted in a ROU asset of approximately $161 million from operating leases for our various corporate facilities, a $29 million reduction to accrued expenses and other liabilities for accrued rent and unamortized tenant improvement allowances, and a lease liability of approximately $190 million. The adoption did not change our previously reported Condensed Consolidated Statements of Comprehensive Income and did not result in a cumulative catch-up adjustment to opening retained earnings. Receivables—Nonrefundable Fees and Other Costs: Premium Amortization on Purchased Callable Debt Securities (ASU 2017-08) In March 2017, the FASB issued ASU 2017-08. The amendments in this update require premiums on purchased callable debt securities to be amortized to the security’s earliest call date. Prior to this ASU, premiums and discounts on purchased callable debt securities were generally required to be amortized to the security’s maturity date. The amendments do not require an accounting change for securities held at a discount. We adopted the amendments on January 1, 2019, on a modified retrospective basis, which resulted in an increase to our accumulated deficit of $10 million, net of income taxes, partially offset by an $8 million decrease to accumulated other comprehensive loss, net of income taxes. Recently Issued Accounting Standards Financial Instruments—Credit Losses (ASU 2016-13) In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (CECL). The amendments in this update introduce a new accounting model to measure credit losses for financial assets measured at amortized cost. The FASB has also issued additional ASUs to clarify the scope and provide additional guidance for ASU 2016-13. Credit losses for financial assets measured at amortized cost should be determined based on the total current expected credit losses over the life of the financial asset or group of financial assets. In effect, the financial asset or group of financial assets should be presented at the net amount expected to be collected. Credit losses will no longer be recorded under the current incurred loss model for financial assets measured at amortized cost. The amendments also modify the accounting for available-for-sale debt securities whereby credit losses will be recorded through an allowance for credit losses rather than a write-down to the security’s cost basis, which allows for reversals of credit losses when estimated credit losses decline. Credit losses for available-for-sale debt securities should be measured in a manner similar to current GAAP. The amendments are effective on January 1, 2020, and must be applied using a modified retrospective approach with a cumulative-effect adjustment through retained earnings as of the beginning of the fiscal year upon adoption as required. While the standard modifies the measurement of the allowance for credit losses, it does not alter the credit risk of our loan portfolios. Management has continued to utilize a cross-functional working group to govern the implementation of these amendments, including consideration of model development, data integrity, technology, reporting and disclosure requirements, key accounting interpretations, control environment, and corporate governance. We are in the process of finalizing the allowance for credit loss models, implementing changes to our internal processes and internal control structure, and updating our policies and documentation related to the allowance for credit losses. During the third quarter of 2019, we performed parallel testing, which included enhanced analytics, continued refinement of our qualitative allowance framework, and the execution of parallel processes for governance and documentation, and we expect to complete our implementation efforts by December 31, 2019. Based on forecasted economic conditions and portfolio balances as of September 30, 2019, preliminary assessments indicate that the adoption of CECL could result in an overall increase to our allowance for loan losses on finance receivables and loans of between 105% to 115%. The increase is driven by our consumer automotive loan portfolio and is primarily related to the difference between loss emergence periods currently utilized, as compared to estimating lifetime credit losses as required by the CECL standard. Additionally, there was no material impact to the allowance for loan losses from our other loan portfolios. Our estimation techniques under CECL are impacted by forecasted economic conditions. Our modeling processes utilize a 12 month reasonable and supportable forecast period for all portfolio segments. After the forecast period, we revert to a longer term historical mean over a 24 month period. Additionally, the adoption of CECL is not expected to result in a material impact to our held-to-maturity securities portfolio, which is primarily composed of agency-backed mortgage securities, and is also not expected to have a material impact on our available-for-sale debt securities portfolio. The actual impact of adopting this standard will depend upon a number of factors at the adoption date, including the composition and credit quality of our financing receivables and loan portfolios and investment securities portfolios, economic conditions and forecasts, the allowance for credit loss models that are used, the data that is included in the models, the associated qualitative allowance framework, and our estimation techniques. Additionally, under CECL, changes in these factors after the adoption date may lead to increased volatility in our future provisions for loan losses. The impact of the adoption will be reflected as an adjustment to beginning retained earnings, net of income taxes. Additionally, we currently expect to phase in the day-one impact of CECL into regulatory capital as prescribed by regulatory capital rules which permit us to phase in 25 percent of the capital impact of CECL in 2020 and an additional 25 percent each subsequent year until fully-phased in by the first quarter of 2023.

Ally Financial Inc. (together with its consolidated subsidiaries unless the context otherwise requires, Ally, the Company, or we, us, or our) is a leading digital financial-services company. As a customer-centric company with passionate customer service and innovative financial solutions, we are relentlessly focused on “Doing It Right” and being a trusted financial-services provider to our consumer, commercial, and corporate customers. We are one of the largest full-service automotive finance operations in the country and offer a wide range of financial services and insurance products to dealerships and consumers. Our award-winning online bank (Ally Bank, Member Federal Deposit Insurance Corporation and Equal Housing Lender) offers mortgage-lending services and a variety of deposit and other banking products, including savings, money-market, and checking accounts, certificates of deposit (CDs), and individual retirement accounts (IRAs). Additionally, we offer securities-brokerage and investment-advisory services through Ally Invest. Our robust corporate finance business offers capital for equity sponsors and middle-market companies. We are a Delaware corporation and are registered as a bank holding company (BHC) under the Bank Holding Company Act of 1956, as amended, and a financial holding company (FHC) under the Gramm-Leach-Bliley Act of 1999, as amended.

Our accounting and reporting policies conform to accounting principles generally accepted in the United States of America (GAAP). Additionally, where applicable, the policies conform to the accounting and reporting guidelines prescribed by bank regulatory authorities. 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 September 30, 2019, and for the three months and nine months ended September 30, 2019, and 2018, 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, 2018, as filed on February 20, 2019, with the U.S. Securities and Exchange Commission (SEC).

At contract inception, we determine whether the contract is or contains a lease based on the terms and conditions of the contract. Lease contracts are recognized on our Condensed Consolidated Balance Sheet as right-of-use (ROU) assets and lease liabilities; however, we have elected not to recognize ROU assets and lease liabilities on real estate leases with terms of one year or less. Lease liabilities and their corresponding ROU assets are recorded based on the present value of the future lease payments over the expected lease term. As the interest rate implicit in the lease contract is typically not readily determinable, we utilize our incremental borrowing rate, which is the rate we would incur to borrow on a collateralized basis over a similar term on an amount equal to the lease payments in a similar economic environment. The ROU asset also includes initial direct costs paid less lease incentives received from the lessor. Our lease contracts are generally classified as operating and, as a result, we recognize a single lease cost within other operating expenses on the income statement on a straight-line basis over the lease term. This update to our accounting policy resulted from our adoption of Accounting Standards Update (ASU) 2016-02 on January 1, 2019, as further described within the section below titled Recently Adopted Accounting Standards.

Premiums on debt securities that have noncontingent call features that are callable at fixed prices on preset dates are amortized to the earliest call date as an adjustment to investment yield. All other premiums and discounts on debt securities are amortized over the stated maturity of the security as an adjustment to investment yield. This method of amortization differs from that described in Note 1 to the Consolidated Financial Statements in our 2018 Annual Report on Form 10-K, which describes our full accounting policy for Investments. This update to our amortization methodology resulted from the adoption of ASU 2017-08 on January 1, 2019, as further described within the section below titled Recently Adopted Accounting Standards.

In calculating the provision for interim income taxes, in accordance with Accounting Standards Codification (ASC) Topic 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 2018 Annual Report on Form 10-K, which describes our annual significant income tax accounting policy and related methodology.

In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02. The amendments in this update primarily replaced the existing accounting requirements for operating leases for lessees. Lessee accounting requirements for finance leases (previously referred to as capital leases) and lessor accounting requirements for operating leases and sales type and direct financing leases were largely unchanged. The amendments require the lessee of an operating lease to record a balance sheet gross-up upon lease commencement by recognizing a ROU asset and lease liability equal to the present value of the lease payments. The ROU asset and lease liability should be derecognized in a manner that effectively yields a straight line lease expense over the lease term. In addition to the changes to the lessee operating lease accounting requirements, the amendments also changed the types of costs that can be capitalized related to a lease agreement for both lessees and lessors. The amendments also require additional disclosures for all lease types for both lessees and lessors. The FASB issued additional ASUs to clarify the guidance and provide certain practical expedients and an additional transition option. We adopted ASU 2016-02 and the subsequent ASUs that modified ASU 2016-02 (collectively, the amendments) on January 1, 2019. This includes the early adoption of ASU 2019-01, which was issued in March 2019 to amend certain provisions included in ASU 2016-02.

We adopted this guidance using the modified retrospective approach on January 1, 2019, and have not adjusted prior period comparative information and will continue to disclose prior period financial information in accordance with the previous lease accounting guidance. We have elected certain practical expedients permitted within the amendments that allowed us to not reassess (i) current lease classifications, (ii) whether existing contracts meet the definition of a lease under the amendments to the lease guidance, and (iii) whether current initial direct costs meet the new criteria for capitalization, for all existing leases as of the adoption date. We made an accounting policy election to calculate the impact of adoption using the remaining minimum lease payments and remaining lease term for each contract that was identified as a lease, discounted at our incremental borrowing rate as of the adoption date. The adoption of the amendments resulted in a ROU asset of approximately $161 million from operating leases for our various corporate facilities, a $29 million reduction to accrued expenses and other liabilities for accrued rent and unamortized tenant improvement allowances, and a lease liability of approximately $190 million. The adoption did not change our previously reported Condensed Consolidated Statements of Comprehensive Income and did not result in a cumulative catch-up adjustment to opening retained earnings.

In March 2017, the FASB issued ASU 2017-08. The amendments in this update require premiums on purchased callable debt securities to be amortized to the security’s earliest call date. Prior to this ASU, premiums and discounts on purchased callable debt securities were generally required to be amortized to the security’s maturity date. The amendments do not require an accounting change for securities held at a discount. We adopted the amendments on January 1, 2019, on a modified retrospective basis, which resulted in an increase to our accumulated deficit of $10 million, net of income taxes, partially offset by an $8 million decrease to accumulated other comprehensive loss, net of income taxes.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (CECL). The amendments in this update introduce a new accounting model to measure credit losses for financial assets measured at amortized cost. The FASB has also issued additional ASUs to clarify the scope and provide additional guidance for ASU 2016-13. Credit losses for financial assets measured at amortized cost should be determined based on the total current expected credit losses over the life of the financial asset or group of financial assets. In effect, the financial asset or group of financial assets should be presented at the net amount expected to be collected. Credit losses will no longer be recorded under the current incurred loss model for financial assets measured at amortized cost. The amendments also modify the accounting for available-for-sale debt securities whereby credit losses will be recorded through an allowance for credit losses rather than a write-down to the security’s cost basis, which allows for reversals of credit losses when estimated credit losses decline. Credit losses for available-for-sale debt securities should be measured in a manner similar to current GAAP. The amendments are effective on January 1, 2020, and must be applied using a modified retrospective approach with a cumulative-effect adjustment through retained earnings as of the beginning of the fiscal year upon adoption as required. While the standard modifies the measurement of the allowance for credit losses, it does not alter the credit risk of our loan portfolios.

Management has continued to utilize a cross-functional working group to govern the implementation of these amendments, including consideration of model development, data integrity, technology, reporting and disclosure requirements, key accounting interpretations, control environment, and corporate governance. We are in the process of finalizing the allowance for credit loss models, implementing changes to our internal processes and internal control structure, and updating our policies and documentation related to the allowance for credit losses. During the third quarter of 2019, we performed parallel testing, which included enhanced analytics, continued refinement of our qualitative allowance framework, and the execution of parallel processes for governance and documentation, and we expect to complete our implementation efforts by December 31, 2019. Based on forecasted economic conditions and portfolio balances as of September 30, 2019, preliminary assessments indicate that the adoption of CECL could result in an overall increase to our allowance for loan losses on finance receivables and loans of between 105% to 115%. The increase is driven by our consumer automotive loan portfolio and is primarily related to the difference between loss emergence periods currently utilized, as compared to estimating lifetime credit losses as required by the CECL standard. Additionally, there was no material impact to the allowance for loan losses from our other loan portfolios. Our estimation techniques

under CECL are impacted by forecasted economic conditions. Our modeling processes utilize a 12 month reasonable and supportable forecast period for all portfolio segments. After the forecast period, we revert to a longer term historical mean over a 24 month period. Additionally, the adoption of CECL is not expected to result in a material impact to our held-to-maturity securities portfolio, which is primarily composed of agency-backed mortgage securities, and is also not expected to have a material impact on our available-for-sale debt securities portfolio.

The actual impact of adopting this standard will depend upon a number of factors at the adoption date, including the composition and credit quality of our financing receivables and loan portfolios and investment securities portfolios, economic conditions and forecasts, the allowance for credit loss models that are used, the data that is included in the models, the associated qualitative allowance framework, and our estimation techniques. Additionally, under CECL, changes in these factors after the adoption date may lead to increased volatility in our future provisions for loan losses. The impact of the adoption will be reflected as an adjustment to beginning retained earnings, net of income taxes. Additionally, we currently expect to phase in the day-one impact of CECL into regulatory capital as prescribed by regulatory capital rules which permit us to phase in 25 percent of the capital impact of CECL in 2020 and an additional 25 percent each subsequent year until fully-phased in by the first quarter of 2023.