Summary of Significant Accounting Policies	3 Months Ended
Mar. 31, 2012
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation - FirstMerit Corporation (“the Parent Company”) is a bank holding company whose principal asset is the common stock of its wholly-owned subsidiary, FirstMerit Bank, N. A. (the “Bank”). The Parent Company’s other subsidiaries include Citizens Savings Corporation of Stark County, FirstMerit Capital Trust I, FirstMerit Community Development Corporation, FirstMerit Risk Management, Inc., and FMT, Inc. All significant intercompany balances and transactions have been eliminated in consolidation. The accounting and reporting policies of FirstMerit Corporation and its subsidiaries (the “Corporation”) conform to generally accepted accounting principles in the United States of America (“U.S. GAAP”) and to general practices within the financial services industry. The consolidated balance sheet at December 31, 2011 has been derived from the audited consolidated financial statements at that date. The accompanying unaudited interim financial statements reflect all adjustments (consisting only of normally recurring adjustments) that are, in the opinion of FirstMerit Corporation’s Management (“Management”), necessary for a fair statement of the results for the interim periods presented. Certain information and note disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been omitted in accordance with the rules of the Securities and Exchange Commission (“SEC”). The unaudited consolidated financial statements of the Corporation as of March 31, 2012 and 2011 are not necessarily indicative of the results that may be achieved for the full fiscal year or for any future period. These unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2011 (the “2011 Form 10-K”). Certain reclassifications of prior year’s amounts have been made to conform to the current year presentation. Such reclassifications had no effect on net earnings or equity. There have been no significant changes to the Corporation’s accounting policies as disclosed in the Annual Report on Form 10-K for the year ended December 31, 2011. In preparing these accompanying unaudited interim consolidated financial statements, subsequent events were evaluated through the time the consolidated financial statements were issued. No material subsequent events have occurred requiring recognition in the consolidated financial statements or disclosure in the notes to the consolidated financial statements. Recently Adopted and Issued Accounting Standards - FASB ASU 2011-03, Reconsideration of Effective Control for Repurchase Agreements. ASU 2011-03 removes from the assessment of effective control (1) the criterion requiring the transferor to have the ability to repurchase or redeem the financial assets on substantially the agreed terms, even in the event of default by the transferee, and (2) the collateral maintenance implementation guidance related to that criterion. Other criteria applicable to the assessment of effective control are not changed by the amendments in the update. ASU 2011-03 is effective prospectively for all transactions or modifications of existing transactions that occur on or after January 1, 2012. ASU 2011-03 did not have a significant impact on the Corporation's consolidated financial statements. FASB ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs. This amendment was issued as result of an effort to develop common fair value measurement and disclosure requirements in U.S. GAAP and International Financial Reporting Standards (“IFRSs”). While ASU 2011-04 is largely consistent with existing fair value measurement principles under U.S. GAAP, it expands the disclosure requirements for fair value measurements and clarifies the existing guidance or wording changes to align with IRFS No. 13. Many of the requirements for the amendments in ASU 2011-04 do not result in a change in the application of the requirements in ASC 820. ASU 2011-04 was effective for the Corporation on a prospective basis beginning in the quarter ended March 31, 2012. The adoption of ASU 2011-04 did not have a significant impact on the Corporation's consolidated financial statements. The newly required disclosures are incorporated into Note 11 (Fair Value Measurement). FASB ASU 2011-05, Presentation of Comprehensive Income. ASU 2011-05 provides entities with the option to present the total of comprehensive income, the components of net income, and the components of other comprehensive income either in a single continuous statement of comprehensive income or in two separate but consecutive statements. In both choices, an entity is required to present each component of net income along with total net income, each component of other comprehensive income, along with a total for other comprehensive income, and a total amount for comprehensive income. As originally issued, ASU 2011-05 required entities to present reclassification adjustments out of accumulated other comprehensive income by component in the statement in which net income is presented and the statement in which other comprehensive income is presented. This requirement was deferred by ASU 2011-12, Deferral of the Effective Date for Amendments to the Presentation of Reclassifications of Items Out of Accumulated Other Comprehensive Income in Accounting Standards Update No. 2011-05. ASU 2011-05 was effective for the Corporation on a retrospective basis beginning in the quarter ended March 31, 2012. The adoption of ASU 2011-05 did not have an impact on the Corporation's financial statements as the Corporation reports comprehensive income in a single continuous statement with all of the components required by ASU 2011-05. FASB ASU 2011-08, Testing Goodwill for Impairment. ASU 2011-08 amends the guidance in ASC 350-20 on testing goodwill for impairment and provides the option of performing a qualitative assessment of whether it is more likely than not that a reporting unit's fair value is less than its carrying amount, before applying the current two-step goodwill impairment test. If the entity determines that the fair value of the reporting unit is more likely than not less than the carrying amount, the two-step impairment test would be required. Otherwise, the entity would not need to apply the two-step test. ASU 2011-08 is effective for annual and interim goodwill impairment tests performed for fiscal years beginning after December 15, 2011. The Corporation has not had to test goodwill for impairment since ASU 2011-08 became effective for the Corporation, January 1, 2012. ASU 2011-08 is not expected to have a significant impact on the Corporation's consolidated financial statements. FASB ASU 2011-11, Disclosures about Offsetting Assets and Liabilities. ASU 2011-11 amends the guidance in ASC 210, Balance Sheet, to require an entity to disclose information about offsetting and related arrangements to enable users of an entity's financial statements to evaluate the effect or potential effect of netting arrangements with certain financial instruments and derivative instruments. The amendments are effective for annual reporting periods beginning on or after January 1, 2013, with retrospective application to the disclosures of all comparative periods presented. The Corporation has not completed evaluating the impact of ASU 2011-11 on its consolidated financial statements.

Summary of Significant Accounting Policies

Basis of Presentation - FirstMerit Corporation (“the Parent Company”) is a bank holding company whose principal asset is the common stock of its wholly-owned subsidiary, FirstMerit Bank, N. A. (the “Bank”). The Parent Company’s other subsidiaries include Citizens Savings Corporation of Stark County, FirstMerit Capital Trust I, FirstMerit Community Development Corporation, FirstMerit Risk Management, Inc., and FMT, Inc. All significant intercompany balances and transactions have been eliminated in consolidation.

The accounting and reporting policies of FirstMerit Corporation and its subsidiaries (the “Corporation”) conform to generally accepted accounting principles in the United States of America (“U.S. GAAP”) and to general practices within the financial services industry.

The consolidated balance sheet at December 31, 2011 has been derived from the audited consolidated financial statements at that date. The accompanying unaudited interim financial statements reflect all adjustments (consisting only of normally recurring adjustments) that are, in the opinion of FirstMerit Corporation’s Management (“Management”), necessary for a fair statement of the results for the interim periods presented. Certain information and note disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been omitted in accordance with the rules of the Securities and Exchange Commission (“SEC”). The unaudited consolidated financial statements of the Corporation as of March 31, 2012 and 2011 are not necessarily indicative of the results that may be achieved for the full fiscal year or for any future period. These unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2011 (the “2011 Form 10-K”). Certain reclassifications of prior year’s amounts have been made to conform to the current year presentation. Such reclassifications had no effect on net earnings or equity.

There have been no significant changes to the Corporation’s accounting policies as disclosed in the Annual Report on Form 10-K for the year ended December 31, 2011.

In preparing these accompanying unaudited interim consolidated financial statements, subsequent events were evaluated through the time the consolidated financial statements were issued. No material subsequent events have occurred requiring recognition in the consolidated financial statements or disclosure in the notes to the consolidated financial statements.

Recently Adopted and Issued Accounting Standards -

FASB ASU 2011-03, Reconsideration of Effective Control for Repurchase Agreements. ASU 2011-03 removes from the assessment of effective control (1) the criterion requiring the transferor to have the ability to repurchase or redeem the financial assets on substantially the agreed terms, even in the event of default by the transferee, and (2) the collateral maintenance implementation guidance related to that criterion. Other criteria applicable to the assessment of effective control are not changed by the amendments in the update. ASU 2011-03 is effective prospectively for all transactions or modifications of existing transactions that occur on or after January 1, 2012. ASU 2011-03 did not have a significant impact on the Corporation's consolidated financial statements.

FASB ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs. This amendment was issued as result of an effort to develop common fair value measurement and disclosure requirements in U.S. GAAP and International Financial Reporting Standards (“IFRSs”). While ASU 2011-04 is largely consistent with existing fair value measurement principles under U.S. GAAP, it expands the disclosure requirements for fair value measurements and clarifies the existing guidance or wording changes to align with IRFS No. 13. Many of the requirements for the amendments in ASU 2011-04 do not result in a change in the application of the requirements in ASC 820. ASU 2011-04 was effective for the Corporation on a prospective basis beginning in the quarter ended March 31, 2012. The adoption of ASU 2011-04 did not have a significant impact on the Corporation's consolidated financial statements. The newly required disclosures are incorporated into Note 11 (Fair Value Measurement).

FASB ASU 2011-05, Presentation of Comprehensive Income. ASU 2011-05 provides entities with the option to present the total of comprehensive income, the components of net income, and the components of other comprehensive income either in a single continuous statement of comprehensive income or in two separate but consecutive statements. In both choices, an entity is required to present each component of net income along with total net income, each component of other comprehensive income, along with a total for other comprehensive income, and a total amount for comprehensive income. As originally issued, ASU 2011-05 required entities to present reclassification adjustments out of accumulated other comprehensive income by component in the statement in which net income is presented and the statement in which other comprehensive income is presented. This requirement was deferred by ASU 2011-12, Deferral of the Effective Date for Amendments to the Presentation of Reclassifications of Items Out of Accumulated Other Comprehensive Income in Accounting Standards Update No. 2011-05. ASU 2011-05 was effective for the Corporation on a retrospective basis beginning in the quarter ended March 31, 2012. The adoption of ASU 2011-05 did not have an impact on the Corporation's financial statements as the Corporation reports comprehensive income in a single continuous statement with all of the components required by ASU 2011-05.

FASB ASU 2011-08, Testing Goodwill for Impairment. ASU 2011-08 amends the guidance in ASC 350-20 on testing goodwill for impairment and provides the option of performing a qualitative assessment of whether it is more likely than not that a reporting unit's fair value is less than its carrying amount, before applying the current two-step goodwill impairment test. If the entity determines that the fair value of the reporting unit is more likely than not less than the carrying amount, the two-step impairment test would be required. Otherwise, the entity would not need to apply the two-step test. ASU 2011-08 is effective for annual and interim goodwill impairment tests performed for fiscal years beginning after December 15, 2011. The Corporation has not had to test goodwill for impairment since ASU 2011-08 became effective for the Corporation, January 1, 2012. ASU 2011-08 is not expected to have a significant impact on the Corporation's consolidated financial statements.

FASB ASU 2011-11, Disclosures about Offsetting Assets and Liabilities. ASU 2011-11 amends the guidance in ASC 210, Balance Sheet, to require an entity to disclose information about offsetting and related arrangements to enable users of an entity's financial statements to evaluate the effect or potential effect of netting arrangements with certain financial instruments and derivative instruments. The amendments are effective for annual reporting periods beginning on or after January 1, 2013, with retrospective application to the disclosures of all comparative periods presented. The Corporation has not completed evaluating the impact of ASU 2011-11 on its consolidated financial statements.