Significant Accounting Policies (Policies)	6 Months Ended
Significant Accounting Policies (Policies)	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	The accompanying unaudited interim consolidated financial statements have been prepared in accordance with the instructions to the SEC Form 10-Q and Article 10 of Regulation S-X; therefore, they do not include all information and footnotes necessary for a fair presentation of financial position, results of operations, comprehensive income, and cash flows in conformity with GAAP. All adjustments consisting of normally recurring accruals that, in the opinion of management, are necessary for a fair presentation of the consolidated financial position and results of operations for the periods covered by this Report have been included. The accompanying unaudited interim consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes appearing in Synovus' 2017 Form 10-K. In connection with the adoption of ASU 2016-18, Statement of Cash Flows-Restricted Cash, Synovus changed its presentation of cash and cash equivalents, effective January 1, 2018, to include cash and due from banks as well as interest bearing funds with the Federal Reserve Bank, interest earning deposits with banks, and federal funds sold and securities purchased under resale agreements, which are inclusive of any restricted cash and restricted cash equivalents. Prior to 2018, cash and cash equivalents only included cash and due from banks. Prior periods have been revised to maintain comparability. Excluding the aforementioned presentation change, there have been no significant changes to the accounting policies as disclosed in Synovus' 2017 Form 10-K. In preparing the unaudited interim consolidated financial statements in accordance with GAAP, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities as of the date of the respective consolidated balance sheets and the reported amounts of revenues and expenses for the periods presented. Actual results could differ significantly from those estimates. Material estimates that are particularly susceptible to significant change relate to the determination of the allowance for loan losses, the fair value of investment securities, and the fair value of private equity investments.
Cash and Cash Equivalents	Cash and cash equivalents consist of cash and due from banks, interest bearing funds with the Federal Reserve Bank, interest earning deposits with banks, federal funds sold and securities purchased under resale agreements, and is inclusive of any restricted cash and restricted cash equivalents. Restricted cash and restricted cash equivalents primarily relate to cash held on deposit with the Federal Reserve to meet reserve requirements as well as cash posted as collateral for derivatives in a liability position. At June 30, 2018 and December 31, 2017, interest bearing funds with the Federal Reserve Bank included $35.7 million and $8.6 million, respectively, on deposit to meet Federal Reserve Bank requirements. Interest earning deposits with banks include $2.7 million and $5.9 million at June 30, 2018 and December 31, 2017, respectively, which are pledged as collateral in connection with certain letters of credit. Federal funds sold include $30.6 million and $43.8 million at June 30, 2018 and December 31, 2017, respectively, which are pledged to collateralize certain derivative financial instruments. Federal funds sold and securities purchased under resale agreements generally mature in one day.
Income Taxes	On December 22, 2017, Federal Tax Reform was enacted into law. The new legislation included a decrease in the corporate federal income tax rate from 35% to 21% effective January 1, 2018. Under ASC 740, the effects of the changes in tax rates and laws are recognized in the period in which the new legislation is enacted. Therefore, Synovus was required to remeasure its deferred tax assets and liabilities and record the adjustment to income tax expense effective December 22, 2017. In December 2017, the SEC issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (SAB 118), which allowed companies to record provisional amounts during a measurement period not to extend beyond one year of the enactment date. Since Federal Tax Reform was enacted late in 2017, management expects that certain deferred tax assets and liabilities will continue to be evaluated in the context of Federal Tax Reform through the date of the filing of our 2017 federal income tax return, and may change as a result of evolving management interpretations, elections, and assumptions, as well as new guidance that may be issued by the Internal Revenue Service. Accordingly, the federal income tax expense of $47.2 million recorded in 2017 relating to the effects from Federal Tax Reform is considered provisional. Management expects to complete its analysis within the measurement period in accordance with SAB 118.
Recently Adopted Accounting Standards Updates	ASU 2014-09, Revenue from Contracts with Customers (Topic 606) issued by the FASB in May 2014, and all subsequent ASUs that modified 606. ASU 2014-09 implements a common revenue standard that establishes principles for reporting information about the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts to provide goods or services to customers. The core principle of the revenue model is that a company will recognize revenue when it transfers control of goods or services to customers at an amount that reflects the consideration to which it expects to be entitled in exchange for those goods or services. The scope of the guidance explicitly excludes net interest income as well as many other revenues from financial assets. Management reviewed its revenue streams and contracts with customers and did not identify material changes to the timing or amount of revenue recognition. Synovus adopted these ASUs on the required effective date of January 1, 2018 utilizing the modified retrospective method of adoption. The adoption resulted in a cumulative effect adjustment of ($685) thousand to the opening balance of retained earnings. Beginning January 1, 2018, in connection with the adoption of this standard, Synovus began including merchant discounts and other card-related fees in card fees. For periods prior to January 1, 2018, these amounts were previously presented in other non-interest income and have been reclassified for comparability. See "Part I - Item 1. Financial Statements and Supplementary Data - Note 12 - Non-interest Income" for the required disclosures in accordance with this ASU. ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. In February 2018, the FASB issued final guidance on reclassification of tax effects stranded in other comprehensive income due to Federal Tax Reform. The guidance provides entities the option to reclassify the tax effects that are stranded in accumulated other comprehensive income, or AOCI, as a result of Federal Tax Reform to retained earnings. The guidance is effective for fiscal years beginning after December 15, 2018; early adoption is permitted. Synovus elected to early adopt ASU 2018-02 as of January 1, 2018 and elected to reclassify the income tax effects of Federal Tax Reform from AOCI to retained earnings. For Synovus, tax effects stranded in AOCI due to Federal Tax Reform totaled $7.6 million at December 31, 2017 and primarily related to unrealized losses on the available-for-sale investment securities portfolio. The reclassification adjustment resulted in an increase to retained earnings as of January 1, 2018 of $7.6 million and a corresponding decrease to AOCI for the same amount. ASU 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities. In January 2016, the FASB issued ASU 2016-01 that included targeted amendments to accounting guidance for recognition, measurement, presentation, and disclosure of financial instruments. ASU 2016-01 requires equity investments (except those accounted for under the equity method of accounting or consolidated) to be measured at fair value with changes in fair value recognized in net income. This ASU requires a cumulative-effect adjustment to retained earnings as of the beginning of the reporting period of adoption to reclassify the cumulative change in fair value of equity securities previously recognized in AOCI. ASU 2016-01 became effective for Synovus on January 1, 2018. The adoption of the guidance resulted in a transfer of investments in mutual funds of $3.2 million, at fair value, from investment securities available for sale to other assets and a $117 thousand cumulative-effect adjustment that decreased retained earnings, with offsetting related adjustments to deferred taxes and AOCI. ASU 2016-01 also emphasizes the existing requirement to use an exit price concept to measure fair value for disclosure purposes in determining the fair value of loans. Determination of the fair value under the exit price method requires judgment because substantially all of the loans within the loan portfolio do not have observable market prices. The adoption of this guidance did not have a significant impact on Synovus' fair value disclosures.
Reclassifications	Prior periods' consolidated financial statements are reclassified whenever necessary to conform to the current periods' presentation.
Revenue from Contracts with Customers	Following is a discussion of key revenues within the scope of the new revenue guidance: Service Charges on Deposit Accounts: Revenue from service charges on deposit accounts is earned through cash management, wire transfer, and other deposit-related services, as well as overdraft, non-sufficient funds, account management and other deposit-related fees. Revenue is recognized for these services either over time, corresponding with deposit accounts' monthly cycle, or at a point in time for transaction related services and fees. Payment for service charges on deposit accounts is primarily received immediately or in the following month through a direct charge to customers' accounts. Fiduciary and Asset Management Fees: Fiduciary and asset management fees are primarily comprised of fees earned from the management and administration of trusts and other customer assets. Synovus' performance obligation is generally satisfied over time and the resulting fees are recognized monthly, based upon the month-end market value of the assets under management and the applicable fee rate. Payment is generally received a few days after month-end through a direct charge to customers' accounts. Synovus does not earn performance-based incentives. Card Fees: Card fees consist primarily of interchange fees from consumer credit and debit cards processed by card association networks, as well as merchant discounts, and other card related services. Interchange rates are generally set by the credit card associations and based on purchase volumes and other factors. Interchange fees and merchant discounts are recognized concurrently with the delivery of service on a daily basis as transactions occur. Payment is typically received immediately or in the following month. Card fees are reported net of certain associated expense items including loyalty program expenses and network expenses. Brokerage Revenue: Brokerage revenue consists primarily of commissions. Additionally, brokerage revenue includes advisory fees earned from the management of customer assets. Advisory fees for brokerage services are recognized and collected monthly and are based upon the month-end market value of the assets under management at a rate predetermined in the contract. Transactional revenues are based on the size and number of transactions executed at the client's direction and are generally recognized on the trade date with payment received on the settlement date. Insurance Revenue: Insurance revenue primarily consists of commissions received on annuity and life product sales. The commissions are recognized as revenue when the customer executes an insurance policy with the insurance carrier. In some cases, Synovus receives payment of trailing commissions each year when the customer pays its annual premium. For the six and three months ended June 30, 2018, Synovus recognized an immaterial amount of insurance trailing commissions related to performance obligations satisfied in prior periods. Other Fees: Other fees primarily consist of revenues generated from safe deposit box rental fees and lockbox services. Fees are recognized over time, on a monthly basis, as Synovus' performance obligation for services is satisfied. Payment is received upfront for safe deposit box rentals and in the following month for lockbox services. Contract Balances A contract asset balance occurs when an entity performs a service for a customer before the customer pays consideration (resulting in a contract receivable) or before payment is due (resulting in a contract asset). A contract liability balance is an entity's obligation to transfer a service to a customer for which the entity has already received payment (or payment is due) from the customer. Synovus' non-interest revenue streams are largely based on transactional activity, or standard month-end revenue accruals such as asset management fees based on month-end market values. Consideration is often received immediately or shortly after Synovus satisfies its performance obligation and revenue is recognized. Synovus does not typically enter into long-term revenue contracts with customers, and therefore, does not experience significant contract balances. As of June 30, 2018 and December 31, 2017, Synovus did not have any significant contract balances.

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.