Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	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 U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the related disclosure, including those of contingent assets and liabilities at the date of the financial statements. It also includes estimates related to the income and expenses during the reporting period and the 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, the valuations of automotive operating lease assets and residuals, the fair value of financial instruments, and the determination of the provision for income taxes.
Income Taxes	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 2024 Annual Report on Form 10-K, which describes our annual significant income tax accounting policy and related methodology.
Recently Issued Accounting Standards	Recently Issued Accounting Standards Improvements to Income Tax Disclosures (ASU 2023-09) In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. The purpose of this guidance is to enhance the rate reconciliation and income taxes paid disclosures. This ASU requires that an entity disclose, on an annual basis, specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. For the state and local income tax category of the rate reconciliation, entities must disclose a qualitative description of the states and local jurisdictions that make up the majority (greater than 50 percent) of the category. For the income taxes paid disclosures, entities will be required to disclose, on an annual basis, the amount of income taxes paid (net of refunds received) disaggregated by federal, state, and foreign taxes. The amendments are effective on January 1, 2025, for annual reporting and will be included in our 2025 Annual Report on Form 10-K. The amendments must be applied using either a prospective or retrospective approach. Management does not expect the impact of these amendments to be material. Expense Disaggregation Disclosures (ASU 2024-03) In November 2024, the FASB issued ASU 2024-03, Income Statement - Reporting Comprehensive Income (Subtopic 220-40): Expense Disaggregation Disclosures. The purpose of this ASU is to provide additional disclosure that will allow investors to better understand an entity’s performance, better assess an entity’s prospects for future cash flows, and more easily compare an entity’s performance over time and in relation to other similar entities. This ASU requires that an entity disclose, on an interim and annual basis, a disaggregation in the notes to the financial statements of certain income statement line items if the line item includes any of the five required expense categories, which are defined as (1) purchases of inventory, (2) employee compensation, (3) depreciation (including amortization of a finance ROU asset and leasehold improvements), (4) intangible asset amortization, and (5) depletion expense. For the “employee compensation” category, banking entities may continue to present compensation expense on the face of the income statement in accordance with Regulation S-X Rule 210.9-04. The disclosure should include a qualitative description of other expenses included within the income statement line item that are otherwise not disaggregated. This ASU also requires entities to disclose their total selling expenses for each reporting period. Selling expenses are not defined within the ASU, which will require entities to determine and disclose how they define selling expenses on an annual basis. The amendments are effective on January 1, 2027, for annual reporting, and for interim reporting thereafter, with early adoption permitted. The amendments must be applied using either a prospective or retrospective approach. Management does not expect the impact of these amendments to be material.
Fair Value Measurements	The following are descriptions of the valuation methodologies used to measure material assets and liabilities at fair value and details of the valuation models, key inputs to those models, and significant assumptions utilized. •Equity securities — We hold various marketable equity securities measured at fair value with changes in fair value recognized in net income. Measurements based on observable market prices are classified as Level 1. •Available-for-sale securities — We carry our available-for-sale securities at fair value based on external pricing sources. We classify our securities as Level 1 when fair value is determined using quoted prices available for the same instruments trading in active markets. We classify our securities as Level 2 when fair value is determined using prices for similar instruments trading in active markets. We perform pricing validation procedures for our available-for-sale securities. •Derivative instruments — We enter into a variety of derivative financial instruments as part of our risk-management strategies. Certain of these derivatives are exchange traded, such as equity options. To determine the fair value of these instruments, we utilize the quoted market prices for those particular derivative contracts; therefore, we classified these contracts as Level 1. We also execute OTC and centrally cleared derivative contracts, such as interest rate swaps, foreign-currency denominated forward contracts, caps, floors, and agency to-be-announced securities. We utilize third-party-developed valuation models that are widely accepted in the market to value these derivative contracts. The specific terms of the contract and market observable inputs (such as interest rate forward curves, interpolated volatility assumptions, or equity pricing) are used in the model. We classified these derivative contracts as Level 2 because all significant inputs into these models were market observable. We also entered into interest rate lock commitments and forward commitments that were executed as part of our mortgage operations, certain of which met the accounting definition of a derivative and therefore were recorded as derivatives on our Condensed Consolidated Balance Sheet. Interest rate lock commitments were valued with unobservable inputs, so they are classified as Level 3. Certain forward commitments are Level 2 and others are Level 3 depending on the valuation model inputs. We purchase automotive finance receivables and loans from third parties as part of forward flow arrangements and, from time-to-time, execute opportunistic ad-hoc bulk purchases. As part of those agreements, we may be required to pay the counterparty at agreed upon measurement dates and determinable amounts if actual credit performance of the acquired loans on the measurement date is better than what was estimated at the time of acquisition. Because these contracts meet the accounting definition of a derivative, we recognize a liability at fair value for these deferred purchase price payments. The fair value of these liabilities is determined using a discounted cash flow method. To estimate cash flows, we utilize various significant assumptions, including market observable inputs (for example, forward interest rates) and internally developed inputs (for example, prepayment speeds, delinquency levels, and expected credit losses). These liabilities are valued using internal loss models with unobservable inputs, and are classified as Level 3. We are required to consider all aspects of nonperformance risk, including our own credit standing, when measuring fair value of derivative assets and liabilities. We reduce credit risk on the majority of our derivatives by entering into legally enforceable agreements that enable the posting and receiving of collateral associated with the fair value of our derivative positions on an ongoing basis. In the event that we do not enter into legally enforceable agreements that enable the posting and receiving of collateral, we will consider our credit risk in the valuation of derivative liabilities through a DVA and the credit risk of our counterparties in the valuation of derivative assets through a CVA, if warranted. When measuring these valuation adjustments, we generally use credit default swap spreads.

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.