Basis of Presentation and Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2020
Accounting Policies [Abstract]
Reclassifications	Prior periods' consolidated financial statements are reclassified whenever necessary to conform to the current periods' presentation.
Use of Estimates in the Preparation of Financial Statements	In preparing the 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 change relate to the determination of the ACL; estimates of fair value, including goodwill impairment assessment; income taxes; and contingent liabilities.
Investment Securities Available for Sale	Investment securities available for sale are carried at fair value with unrealized gains and losses, net of the related tax effect, excluded from earnings and reported as a separate component of shareholders' equity within accumulated other comprehensive income (loss) until realized. For investment securities available for sale in an unrealized loss position, if Synovus has an intention to sell the security, or it is more likely than not that the security will be required to be sold prior to recovery, the security is written down to its fair value. The write down is charged against the ACL with any additional impairment recorded in earnings. If the aforementioned criteria is not met, Synovus performs a quarterly assessment of its available for sale debt securities to determine if the decline in fair value of a security below its amortized cost is related to credit losses or other factors. Management considers the extent to which fair value is less than amortized cost, the issuer of the security, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. In assessing whether credit related impairment exists, the present value of cash flows expected to be collected from the security is compared to the security's amortized cost. If the present value of cash flows expected to be collected is less than the security's amortized cost basis, the difference is attributable to credit losses. For such differences, Synovus records an ACL with an offset to provision for credit losses expense. Synovus limits the ACL recorded to the amount the security's fair value is less than the amortized cost basis. Impairment losses related to other factors are recognized in other comprehensive income (loss). Accrued interest on available for sale debt securities is excluded from the ACL determination and is recognized within other assets on the consolidated balance sheets. Available-for-sale debt securities are placed on non-accrual status when we no longer expect to receive all contractual amounts due, which is generally at 90 days past due. Accrued interest receivable is reversed against interest income when a security is placed on non-accrual status. Accordingly, we do not recognize an allowance for credit loss against accrued interest receivable.
Loans and Interest Income	Loans the Company has the intent and ability to hold for the foreseeable future are reported at principal amounts outstanding less amounts charged off, net of deferred fees and costs, and purchase premiums/discounts. Interest income, net deferred fees, and purchase premium/discount amortization/accretion on loans, are recognized on a level yield basis. Allowance for Credit Losses for Loans Held for Investment (ALL) The allowance for credit losses on loans held for investment are included in the ALL and represent management's estimate of credit losses expected over the life of the loans included in Synovus' existing loans held for investment portfolio. Changes to the allowance are recorded through a provision for credit losses and reduced by loans charged-off, net of recoveries. Determining the appropriateness of the allowance is complex and requires judgment by management about the effect of matters that are inherently uncertain. Accrued but uncollected interest is recorded in other assets on the consolidated balance sheets. In general, the Company does not record an ACL for accrued interest receivables as allowable per ASC 326-20-30-5A as Synovus' non-accrual policies result in the timely write-off of accrued but uncollected interest. Credit loss measurement Synovus' loan loss estimation process includes procedures to appropriately consider the unique characteristics of its loan portfolio segments (C&I, CRE and consumer). These segments are further disaggregated into loan classes, the level at which credit quality is assessed and monitored (as described in the subsequent sections). The ALL is measured on a collective (pool) basis when similar risk characteristics exist. Loans are grouped based upon the nature of the loan type and are further segregated based upon the individual loan risk ratings. Credit loss assumptions are primarily estimated using a DCF model applied to the aforementioned loan groupings. This model calculates an expected life-of-loan loss percentage for each loan category by considering the forecasted PD, which is the probability that a borrower will default, adjusted for relevant forecasted macroeconomic factors, and LGD, which is the estimate of the amount of net loss in the event of default. Expected credit losses are estimated over the contractual term of the loan, adjusted for expected prepayments and curtailments when appropriate. Management's determination of the contract term excludes expected extensions, renewals, and modifications unless either of the following applies: there is a reasonable expectation at the reporting date that a TDR will be executed with an individual borrower, or an extension or renewal option is included in the contract at the reporting date that is not unconditionally cancellable by Synovus. To the extent the lives of the loans in the portfolio extend beyond the period for which a reasonable and supportable forecast can be made (which is one year for Synovus), the Company reverts, on a straight-line basis back to the historical rates over a one year period. Life-of-loan loss percentages may also be adjusted, as necessary, for certain quantitative and qualitative factors that in management's judgment are necessary to reflect losses expected in the portfolio. These adjustments address inherent limitations in the quantitative model including uncertainty and limitations, among others. The above reflects the ALL estimation process for most commercial and consumer sub-pools. In some cases, Synovus may apply other acceptable loss rate models to smaller subpools. Loans that do not share risk characteristics are individually evaluated on a loan by loan basis with specific reserves, if any, recorded as appropriate. Specific reserves are determined based on two methods: discounted cash flow based upon the loan's contractual effective interest rate or at the fair value of the collateral, less costs to sell if the loan is collateral-dependent. For individually evaluated loans, under the DCF method, resulting expected credit losses are recorded as a specific reserve with a charge-off for any portion of the expected credit loss that is determined not to be recoverable. The reserve is reassessed each quarter and adjusted as appropriate based on changes in estimated cash flows. Additionally, where guarantors are determined to be a source of repayment, an assessment of the guarantee is required. This guarantee assessment would include, but not be limited to, factors such as type and feature of the guarantee, consideration for the guarantor's financial strength and capacity to service the loan in combination with the guarantor's other financial obligations as well as the guarantor's willingness to assist in servicing the loan. For individually evaluated loans, if the loan is collateral-dependent, then the fair value of the loan's collateral, less estimated selling costs, is compared to the loan's carrying amount to determine impairment. Fair value is estimated using appraisals performed by a certified or licensed appraiser. Management also considers other factors or recent developments, such as changes in absorption rates or market conditions at the time of valuation, selling costs and anticipated sales values, taking into account management's plans for disposition, which could result in adjustments to the fair value estimates indicated in the appraisals. The assumptions used in determining the amount of the impairment are subject to significant judgment. Use of different assumptions, for example, changes in the fair value of the collateral or management's plans for disposition could have a significant impact on the amount of impairment. Troubled debt restructurings The ALL on a TDR is measured using the same method as all other loans held for investment, except that the original interest rate, and not the rate specified with the restructuring, is used to discount the expected cash flows. Purchased Loans with Credit Deterioration Purchased loans are evaluated upon acquisition in order to determine if the loan, or pool of loans, has experienced more-than-insignificant deterioration in credit quality since origination or issuance. In the performance of this evaluation, Synovus considers migration of the credit quality of the loans at origination in comparison to the credit quality at acquisition. Purchased loans classified as PCD are recognized in accordance with ASC 326-20-30, whereby the amortized cost basis of the PCD asset is ‘grossed-up’ by the initial estimate of credit losses with an offset to the ALL. This acquisition date allowance has no income statement effect. Post-acquisition, any changes in estimates of expected credit losses are recorded through the provision for credit losses. Non-credit discounts or premiums are accreted or amortized, respectively into interest income using the interest method. Loans formerly accounted for as purchased credit-impaired in accordance with ASC 310-30 were automatically transitioned to PCD classification. The Company did not maintain ASC 310-30 pools. PCD loans were integrated into existing pool structures based upon the nature of the loan type and are further segregated based upon the individual loan risk ratings as noted above. The accounting treatment for purchased loans classified as non-PCD is the same as loans held for investment as detailed in the above section. Allowance for Credit Losses on Off-balance-sheet Credit Exposures Synovus maintains a separate ACL for off-balance-sheet credit exposures, including unfunded loan commitments, unless the associated obligation is unconditionally cancellable by the Company. This allowance is included in other liabilities on the consolidated balance sheets with offsetting expense recognized as a component of the provision for credit losses on the consolidated statements of income. The reserve for off-balance-sheet credit exposures considers the likelihood that funding will occur and estimates the expected credit losses on resulting commitments expected to be funded over its estimated life using the estimated loss rates on loans held for investment.

Basis of Presentation and Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2020

Prior periods' consolidated financial statements are reclassified whenever necessary to conform to the current periods' presentation.

Use of Estimates in the Preparation of Financial Statements

In preparing the 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 change relate to the determination of the ACL; estimates of fair value, including goodwill impairment assessment; income taxes; and contingent liabilities.

Investment Securities Available for Sale

Investment securities available for sale are carried at fair value with unrealized gains and losses, net of the related tax effect, excluded from earnings and reported as a separate component of shareholders' equity within accumulated other comprehensive income (loss) until realized.

For investment securities available for sale in an unrealized loss position, if Synovus has an intention to sell the security, or it is more likely than not that the security will be required to be sold prior to recovery, the security is written down to its fair value. The write down is charged against the ACL with any additional impairment recorded in earnings. If the aforementioned criteria is not met, Synovus performs a quarterly assessment of its available for sale debt securities to determine if the decline in fair value of a security below its amortized cost is related to credit losses or other factors. Management considers the extent to which fair value is less than amortized cost, the issuer of the security, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. In assessing whether credit related impairment exists, the present value of cash flows expected to be collected from the security is compared to the security's amortized cost. If the present value of cash flows expected to be collected is less than the security's amortized cost basis, the difference is attributable to credit losses. For such differences, Synovus records an ACL with an offset to provision for credit losses expense. Synovus limits the ACL recorded to the amount the security's fair value is less than the amortized cost basis. Impairment losses related to other factors are recognized in other comprehensive income (loss).

Accrued interest on available for sale debt securities is excluded from the ACL determination and is recognized within other assets on the consolidated balance sheets. Available-for-sale debt securities are placed on non-accrual status when we no longer expect to receive all contractual amounts due, which is generally at 90 days past due. Accrued interest receivable is reversed against interest income when a security is placed on non-accrual status. Accordingly, we do not recognize an allowance for credit loss against accrued interest receivable.

Loans and Interest Income

Loans the Company has the intent and ability to hold for the foreseeable future are reported at principal amounts outstanding less amounts charged off, net of deferred fees and costs, and purchase premiums/discounts. Interest income, net deferred fees, and purchase premium/discount amortization/accretion on loans, are recognized on a level yield basis.

Allowance for Credit Losses for Loans Held for Investment (ALL)

The allowance for credit losses on loans held for investment are included in the ALL and represent management's estimate of credit losses expected over the life of the loans included in Synovus' existing loans held for investment portfolio. Changes to the allowance are recorded through a provision for credit losses and reduced by loans charged-off, net of recoveries. Determining the appropriateness of the allowance is complex and requires judgment by management about the effect of matters that are inherently uncertain.

Accrued but uncollected interest is recorded in other assets on the consolidated balance sheets. In general, the Company does not record an ACL for accrued interest receivables as allowable per ASC 326-20-30-5A as Synovus' non-accrual policies result in the timely write-off of accrued but uncollected interest.

Credit loss measurement

Synovus' loan loss estimation process includes procedures to appropriately consider the unique characteristics of its loan portfolio segments (C&I, CRE and consumer). These segments are further disaggregated into loan classes, the level at which credit quality is assessed and monitored (as described in the subsequent sections).

The ALL is measured on a collective (pool) basis when similar risk characteristics exist. Loans are grouped based upon the nature of the loan type and are further segregated based upon the individual loan risk ratings. Credit loss assumptions are primarily estimated using a DCF model applied to the aforementioned loan groupings. This model calculates an expected life-of-loan loss percentage for each loan category by considering the forecasted PD, which is the probability that a borrower will default, adjusted for relevant forecasted macroeconomic factors, and LGD, which is the estimate of the amount of net loss in the event of default.

Expected credit losses are estimated over the contractual term of the loan, adjusted for expected prepayments and curtailments when appropriate. Management's determination of the contract term excludes expected extensions, renewals, and

modifications unless either of the following applies: there is a reasonable expectation at the reporting date that a TDR will be executed with an individual borrower, or an extension or renewal option is included in the contract at the reporting date that is not unconditionally cancellable by Synovus.

To the extent the lives of the loans in the portfolio extend beyond the period for which a reasonable and supportable forecast can be made (which is one year for Synovus), the Company reverts, on a straight-line basis back to the historical rates over a one year period.

Life-of-loan loss percentages may also be adjusted, as necessary, for certain quantitative and qualitative factors that in management's judgment are necessary to reflect losses expected in the portfolio. These adjustments address inherent limitations in the quantitative model including uncertainty and limitations, among others.

The above reflects the ALL estimation process for most commercial and consumer sub-pools. In some cases, Synovus may apply other acceptable loss rate models to smaller subpools.

Loans that do not share risk characteristics are individually evaluated on a loan by loan basis with specific reserves, if any, recorded as appropriate. Specific reserves are determined based on two methods: discounted cash flow based upon the loan's contractual effective interest rate or at the fair value of the collateral, less costs to sell if the loan is collateral-dependent.

For individually evaluated loans, under the DCF method, resulting expected credit losses are recorded as a specific reserve with a charge-off for any portion of the expected credit loss that is determined not to be recoverable. The reserve is reassessed each quarter and adjusted as appropriate based on changes in estimated cash flows. Additionally, where guarantors are determined to be a source of repayment, an assessment of the guarantee is required. This guarantee assessment would include, but not be limited to, factors such as type and feature of the guarantee, consideration for the guarantor's financial strength and capacity to service the loan in combination with the guarantor's other financial obligations as well as the guarantor's willingness to assist in servicing the loan.

For individually evaluated loans, if the loan is collateral-dependent, then the fair value of the loan's collateral, less estimated selling costs, is compared to the loan's carrying amount to determine impairment. Fair value is estimated using appraisals performed by a certified or licensed appraiser. Management also considers other factors or recent developments, such as changes in absorption rates or market conditions at the time of valuation, selling costs and anticipated sales values, taking into account management's plans for disposition, which could result in adjustments to the fair value estimates indicated in the appraisals. The assumptions used in determining the amount of the impairment are subject to significant judgment. Use of different assumptions, for example, changes in the fair value of the collateral or management's plans for disposition could have a significant impact on the amount of impairment.

Troubled debt restructurings

The ALL on a TDR is measured using the same method as all other loans held for investment, except that the original interest rate, and not the rate specified with the restructuring, is used to discount the expected cash flows.

Purchased Loans with Credit Deterioration

Purchased loans are evaluated upon acquisition in order to determine if the loan, or pool of loans, has experienced more-than-insignificant deterioration in credit quality since origination or issuance. In the performance of this evaluation, Synovus considers migration of the credit quality of the loans at origination in comparison to the credit quality at acquisition.

Purchased loans classified as PCD are recognized in accordance with ASC 326-20-30, whereby the amortized cost basis of the PCD asset is ‘grossed-up’ by the initial estimate of credit losses with an offset to the ALL. This acquisition date allowance has no income statement effect. Post-acquisition, any changes in estimates of expected credit losses are recorded through the provision for credit losses. Non-credit discounts or premiums are accreted or amortized, respectively into interest income using the interest method.

Loans formerly accounted for as purchased credit-impaired in accordance with ASC 310-30 were automatically transitioned to PCD classification. The Company did not maintain ASC 310-30 pools. PCD loans were integrated into existing pool structures based upon the nature of the loan type and are further segregated based upon the individual loan risk ratings as noted above.

The accounting treatment for purchased loans classified as non-PCD is the same as loans held for investment as detailed in the above section.

Allowance for Credit Losses on Off-balance-sheet Credit Exposures

Synovus maintains a separate ACL for off-balance-sheet credit exposures, including unfunded loan commitments, unless the associated obligation is unconditionally cancellable by the Company. This allowance is included in other liabilities on the consolidated balance sheets with offsetting expense recognized as a component of the provision for credit losses on the

consolidated statements of income. The reserve for off-balance-sheet credit exposures considers the likelihood that funding will occur and estimates the expected credit losses on resulting commitments expected to be funded over its estimated life using the estimated loss rates on loans held for investment.