Financial Information (Policy)	9 Months Ended
Sep. 30, 2011
Financial Information [Abstract]
Basis Of Accounting Policy	The unaudited interim Consolidated Condensed Financial Statements of First Horizon National Corporation ("FHN"), including its subsidiaries, have been prepared in conformity with accounting principles generally accepted in the United States of America and follow general practices within the industries in which it operates. This preparation requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. These estimates and assumptions are based on information available as of the date of the financial statements and could differ from actual results. In the opinion of management, all necessary adjustments have been made for a fair presentation of financial position and results of operations for the periods presented. These adjustments are of a normal recurring nature unless otherwise disclosed in this filing. The operating results for the interim 2011 periods are not necessarily indicative of the results that may be expected going forward. For further information, refer to the audited consolidated financial statements in the 2010 Annual Report to shareholders.
New Accounting Pronouncement Or Change In Accounting Principle Policy	*Accounting Changes.* Effective July 1, 2011, FHN adopted the provisions of FASB Accounting Standards Update 2011-02, "A Creditor's Determination of Whether a Restructuring is a Troubled Debt Restructuring" ("ASU 2011-02"). ASU 2011-02 provides that a situation in which a market rate is not readily available is an indicator of a troubled debt restructuring, but not a determinative factor, and that an assessment should consider all modified terms of the restructuring when making a final determination regarding a troubled debt restructuring designation. ASU 2011-02 also provides that a modification that results in a temporary or permanent increase to the contractual interest rate cannot be presumed to be a rate that is at or above market. ASU 2011-02 explicitly precludes creditors from using the borrower's effective rate test in FASB Accounting Standards Codification 470-60, "Debt—Troubled Debt Restructurings by Debtors" ("ASC 470-60") in its evaluation of whether a modification was executed at a market rate. Under the provisions of ASU 2011-02, a borrower that is not currently in default may still be considered to be experiencing financial difficulty when default is probable in the foreseeable future. ASU 2011-02 provides factors that an entity should consider when determining whether a delay in the amount of payments is significant, as insignificant delays in cash flows would not be considered a concession to a borrower under its provisions. Retrospective application to the beginning of the annual period of adoption is required for identification and disclosure purposes, with prospective application for impairment purposes. Disclosure of the total amount of loans and the associated reserves related to those loans that are considered impaired under ASC 310, "Receivables", as a result of the clarification in guidance is required upon initial application. FHN had previously modified its troubled debt restructuring review process and was already in compliance with the provisions of ASU 2011-02. Therefore, the provisions of ASU 2011-02 had no material effect on FHN's statement of condition, results of operations, cash flows, or required disclosures. Effective July 1, 2011, FHN adopted the remaining provisions of FASB Accounting Standards Update 2010-20, "Disclosures about the Credit Quality of Financing Receivables and the Allowance for Credit Losses" ("ASU 2010-20"), related to the enhanced disclosure requirements for modifications of financing receivables. FHN previously adopted the provisions of ASU 2010-20 for certain disclosures about activity that occurs during a reporting period effective January 1, 2011. Additionally, effective December 31, 2010, FHN adopted the provisions of ASU 2010-20 related to disclosures as of the end of a reporting period, and the amendments to the rollforward of the allowance for credit losses. ASU 2010-20 provides enhanced disclosures related to the credit quality of financing receivables and the allowance for credit losses, and provides that new and existing disclosures should be disaggregated based on how an entity develops its allowance for credit losses and how it manages credit exposures. Under the provisions of ASU 2010-20, additional disclosures required for financing receivables include information regarding the aging of past due receivables, credit quality indicators, and modifications of financing receivables. Comparative disclosures are required only for periods ending subsequent to initial adoption. Upon adoption of the provisions of ASU 2010-20 on September 30, 2011, January 1, 2011, and December 31, 2010, respectively, FHN revised its disclosures accordingly. Effective January 1, 2011, FHN adopted the provisions of FASB Accounting Standards Update 2010-06, "Improving Disclosures about Fair Value Measurements" ("ASU 2010-06"), related to the requirement to provide the activity of purchases, sales, issuances, and settlements related to recurring Level 3 measurements on a gross basis in the Level 3 reconciliation. Effective January 1, 2010, FHN adopted all other provisions of ASU 2010-06. ASU 2010-06 updates FASB Accounting Standards Codification 820, "Fair Value Measurements and Disclosures" ("ASC 820") to require disclosure of significant transfers into and out of Level 1 and Level 2 of the fair value hierarchy, as well as disclosure of an entity's policy for determining when transfers between all levels of the hierarchy are recognized. The updated provisions of ASC 820 also require that fair value measurement disclosures be provided by each "class" of assets and liabilities, and that disclosures providing a description of the valuation techniques and inputs used to measure fair value be included for both recurring and nonrecurring fair value measurements classified as either Level 2 or Level 3. Under ASC 820, as amended, separate disclosure is required in the Level 3 reconciliation of total gains and losses recognized in other comprehensive income. Comparative disclosures are required only for periods ending subsequent to initial adoption. Upon adoption of the amendments to ASC 820 on January 1, 2011 and January 1, 2010, respectively, FHN revised its disclosures accordingly. *Accounting Changes Issued but Not Currently Effective.* In September 2011, the FASB issued Accounting Standards Update 2011-08, "Testing Goodwill for Impairment" ("ASU 2011-08"). ASU 2011-08 provides that an entity may first perform a qualitative assessment of whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount, including goodwill, when determining whether it is necessary to perform the current two-step goodwill impairment test discussed in FASB Accounting Standards Codification 350, "Intangibles – Goodwill and Other" ("ASC 350"). Thus, if an entity concludes from its qualitative assessment that it is more likely than not that the fair value of a reporting unit is less than its carrying amount, it must perform the two-step test. ASU 2011-08 provides examples of events and circumstances that should be considered in an evaluation of whether it is more likely than not that the fair value of an entity's reporting unit is less than its carrying amount. The new qualitative indicators replace the guidance currently provided in ASC 350 which is used to determine whether an interim goodwill impairment test is required, and is applicable for assessing whether to perform Step 2 of the goodwill impairment test for reporting units with zero or negative carrying amounts. Under the provisions of ASU 2011-08, entities will be allowed, on the basis of their discretion, to bypass the qualitative assessment for any reporting unit in any period and proceed directly to performing the first step of the two-step goodwill impairment test, and will be able to resume performing the qualitative assessment in any subsequent period. ASU 2011-08 removes the current alternative in ASC 350 which allows for the carryforward of the detailed calculation of the fair value of a reporting unit from one year to the next if certain conditions are met. The provisions of ASU 2011-08 are effective for fiscal years beginning after December 15, 2011, with early adoption permitted. The adoption of the provisions of ASU 2011-08 will have no effect on FHN's statement of condition, results of operations, or cash flows. In June 2011, the FASB issued Accounting Standards Update 2011-05, "Presentation of Comprehensive Income" ("ASU 2011-05"). ASU 2011-05 requires that net income and other comprehensive income be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements. ASU 2011-05 also provides that regardless of the method used to present comprehensive income, presentation is required on the face of the financial statements of reclassification adjustments for items that are reclassified from other comprehensive income to net income. ASU 2011-05 does not change the current option for entities to present components of other comprehensive income gross or net of the effect of income taxes, provided that such tax effects are presented in the statement in which other comprehensive income is presented or disclosed in the notes to the financial statements. The provisions of ASU 2011-05 are effective for periods beginning after December 15, 2011, with retrospective application to all periods presented in the financial statements required. Early adoption of the provisions in ASU 2011-05 is permitted, and no transition disclosures are required upon adoption. FHN is currently assessing the effects of adopting the provisions of ASU 2011-05. In May 2011, the FASB issued Accounting Standards Update 2011-04, "Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs" ("ASU 2011-04"). ASU 2011-04 provides that the highest-and-best use and valuation-premise concepts included in ASC 820 are only relevant when measuring the fair value of nonfinancial assets, thereby prohibiting the grouping of financial instruments for purposes of determining their fair values when the unit of account is specified in other guidance. However, under ASU 2011-04 an exception is permitted which allows an entity to measure the fair value of financial instruments that are managed on the basis of the entity's net exposure to a particular market risk, or to the credit risk of a particular counterparty, on a net basis when certain criteria are met. Such criteria include that there is evidence that the entity manages its financial instruments in that way, the entity applies such accounting policy election consistently from period to period, and the entity is required or has elected to measure those financial assets and financial liabilities at fair value in the statement of financial position at the end of each reporting period. Additionally, to qualify for the exception to the valuation premise, the market risks that are being offset must be substantially the same. ASU 2011-04 also extends ASC 820's prohibition on the use of blockage factors in fair value measurements to all three levels of the fair value hierarchy except for fair value measurements of Level 2 and 3 measurements when market participants would incorporate the premium or discount into the measurement at the level of the unit of account specified in other guidance. ASU 2011-04 also provides that an entity should measure the fair value of its own equity instruments from the perspective of a market participant that holds the instruments as assets. Under ASC 820, as amended, expanded disclosures are required including disclosure of quantitative information about significant unobservable inputs used in Level 3 fair value measurements, a description of the valuation processes used by the entity, and a qualitative discussion about the sensitivity of the measurements. Additional disclosures required under ASU 2011-04 include disclosure of fair value by level for each class of assets and liabilities not recorded at fair value but for which fair value is disclosed, and disclosure of any transfers between Level 1 and Level 2 of the fair value hierarchy and the reasons for those transfers. The provisions of ASU 2011-04 are effective for periods beginning after December 15, 2011, with disclosure of the change, if any, in valuation technique and related inputs resulting from application of the amendments to ASC 820 required upon adoption, along with quantification of the total effect of the change, if practicable. FHN is currently assessing the effects of adopting the provisions of ASU 2011-04. In April 2011, the FASB issued Accounting Standards Update 2011-03, "Reconsideration of Effective Control for Repurchase Agreements" ("ASU 2011-03"). For entities that enter into agreements to transfer financial assets that both entitle and obligate the transferor to repurchase or redeem the financial assets before their maturity, ASU 2011-03 removes from the assessment of effective control under ASC 860, "Transfers and Servicing", 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, as well as the collateral maintenance implementation guidance related to that criterion. Under ASC 860-10, as amended, the remaining criteria related to whether effective control over transferred financial assets has been maintained would still need to be evaluated, including whether the financial assets to be repurchased or redeemed are the same or substantially the same as those transferred, the agreement is to repurchase or redeem them before maturity at a fixed or determinable price, and whether the agreement is entered into contemporaneously with, or in contemplation of, the transfer. The provisions of ASU 2011-03 are effective for periods beginning after December 15, 2011, with prospective application to transactions or modifications of existing transactions that occur on or after the effective date. Since FHN accounts for all of its repurchase agreements as secured borrowings, adopting the provisions of ASU 2011-03 will not have an effect on FHN's statement of condition, results of operations, or cash flows.

Accounting Changes. Effective July 1, 2011, FHN adopted the provisions of FASB Accounting Standards Update 2011-02, "A Creditor's Determination of Whether a Restructuring is a Troubled Debt Restructuring" ("ASU 2011-02"). ASU 2011-02 provides that a situation in which a market rate is not readily available is an indicator of a troubled debt restructuring, but not a determinative factor, and that an assessment should consider all modified terms of the restructuring when making a final determination regarding a troubled debt restructuring designation. ASU 2011-02 also provides that a modification that results in a temporary or permanent increase to the contractual interest rate cannot be presumed to be a rate that is at or above market. ASU 2011-02 explicitly precludes creditors from using the borrower's effective rate test in FASB Accounting Standards Codification 470-60, "Debt—Troubled Debt Restructurings by Debtors" ("ASC 470-60") in its evaluation of whether a modification was executed at a market rate. Under the provisions of ASU 2011-02, a borrower that is not currently in default may still be considered to be experiencing financial difficulty when default is probable in the foreseeable future. ASU 2011-02 provides factors that an entity should consider when determining whether a delay in the amount of payments is significant, as insignificant delays in cash flows would not be considered a concession to a borrower under its provisions. Retrospective application to the beginning of the annual period of adoption is required for identification and disclosure purposes, with prospective application for impairment purposes. Disclosure of the total amount of loans and the associated reserves related to those loans that are considered impaired under ASC 310, "Receivables", as a result of the clarification in guidance is required upon initial application. FHN had previously modified its troubled debt restructuring review process and was already in compliance with the provisions of ASU 2011-02. Therefore, the provisions of ASU 2011-02 had no material effect on FHN's statement of condition, results of operations, cash flows, or required disclosures.

Effective July 1, 2011, FHN adopted the remaining provisions of FASB Accounting Standards Update 2010-20, "Disclosures about the Credit Quality of Financing Receivables and the Allowance for Credit Losses" ("ASU 2010-20"), related to the enhanced disclosure requirements for modifications of financing receivables. FHN previously adopted the provisions of ASU 2010-20 for certain disclosures about activity that occurs during a reporting period effective January 1, 2011. Additionally, effective December 31, 2010, FHN adopted the provisions of ASU 2010-20 related to disclosures as of the end of a reporting period, and the amendments to the rollforward of the allowance for credit losses. ASU 2010-20 provides enhanced disclosures related to the credit quality of financing receivables and the allowance for credit losses, and provides that new and existing disclosures should be disaggregated based on how an entity develops its allowance for credit losses and how it manages credit exposures. Under the provisions of ASU 2010-20, additional disclosures required for financing receivables include information regarding the aging of past due receivables, credit quality indicators, and modifications of financing receivables. Comparative disclosures are required only for periods ending subsequent to initial adoption. Upon adoption of the provisions of ASU 2010-20 on September 30, 2011, January 1, 2011, and December 31, 2010, respectively, FHN revised its disclosures accordingly.

Effective January 1, 2011, FHN adopted the provisions of FASB Accounting Standards Update 2010-06, "Improving Disclosures about Fair Value Measurements" ("ASU 2010-06"), related to the requirement to provide the activity of purchases, sales, issuances, and settlements related to recurring Level 3 measurements on a gross basis in the Level 3 reconciliation. Effective January 1, 2010, FHN adopted all other provisions of ASU 2010-06. ASU 2010-06 updates FASB Accounting Standards Codification 820, "Fair Value Measurements and Disclosures" ("ASC 820") to require disclosure of significant transfers into and out of Level 1 and Level 2 of the fair value hierarchy, as well as disclosure of an entity's policy for determining when transfers between all levels of the hierarchy are recognized. The updated provisions of ASC 820 also require that fair value measurement disclosures be provided by each "class" of assets and liabilities, and that disclosures providing a description of the valuation techniques and inputs used to measure fair value be included for both recurring and nonrecurring fair value measurements classified as either Level 2 or Level 3. Under ASC 820, as amended, separate disclosure is required in the Level 3 reconciliation of total gains and losses recognized in other comprehensive income. Comparative disclosures are required only for periods ending subsequent to initial adoption. Upon adoption of the amendments to ASC 820 on January 1, 2011 and January 1, 2010, respectively, FHN revised its disclosures accordingly.

Accounting Changes Issued but Not Currently Effective. In September 2011, the FASB issued Accounting Standards Update 2011-08, "Testing Goodwill for Impairment" ("ASU 2011-08"). ASU 2011-08 provides that an entity may first perform a qualitative assessment of whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount, including goodwill, when determining whether it is necessary to perform the current two-step goodwill impairment test discussed in FASB Accounting Standards Codification 350, "Intangibles – Goodwill and Other" ("ASC 350"). Thus, if an entity concludes from its qualitative assessment that it is more likely than not that the fair value of a reporting unit is less than its carrying amount, it must perform the two-step test. ASU 2011-08 provides examples of events and circumstances that should be considered in an evaluation of whether it is more likely than not that the fair value of an entity's reporting unit is less than its carrying amount. The new qualitative indicators replace the guidance currently provided in ASC 350 which is used to determine whether an interim goodwill impairment test is required, and is applicable for assessing whether to perform Step 2 of the goodwill impairment test for reporting units with zero or negative carrying amounts. Under the provisions of ASU 2011-08, entities will be allowed, on the basis of their discretion, to bypass the qualitative assessment for any reporting unit in any period and proceed directly to performing the first step of the two-step goodwill impairment test, and will be able to resume performing the qualitative assessment in any subsequent period. ASU 2011-08 removes the current alternative in ASC 350 which allows for the carryforward of the detailed calculation of the fair value of a reporting unit from one year to the next if certain conditions are met. The provisions of ASU 2011-08 are effective for fiscal years beginning after December 15, 2011, with early adoption permitted. The adoption of the provisions of ASU 2011-08 will have no effect on FHN's statement of condition, results of operations, or cash flows.

In June 2011, the FASB issued Accounting Standards Update 2011-05, "Presentation of Comprehensive Income" ("ASU 2011-05"). ASU 2011-05 requires that net income and other comprehensive income be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements. ASU 2011-05 also provides that regardless of the method used to present comprehensive income, presentation is required on the face of the financial statements of reclassification adjustments for items that are reclassified from other comprehensive income to net income. ASU 2011-05 does not change the current option for entities to present components of other comprehensive income gross or net of the effect of income taxes, provided that such tax effects are presented in the statement in which other comprehensive income is presented or disclosed in the notes to the financial statements. The provisions of ASU 2011-05 are effective for periods beginning after December 15, 2011, with retrospective application to all periods presented in the financial statements required. Early adoption of the provisions in ASU 2011-05 is permitted, and no transition disclosures are required upon adoption. FHN is currently assessing the effects of adopting the provisions of ASU 2011-05.

In May 2011, the FASB issued Accounting Standards Update 2011-04, "Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs" ("ASU 2011-04"). ASU 2011-04 provides that the highest-and-best use and valuation-premise concepts included in ASC 820 are only relevant when measuring the fair value of nonfinancial assets, thereby prohibiting the grouping of financial instruments for purposes of determining their fair values when the unit of account is specified in other guidance. However, under ASU 2011-04 an exception is permitted which allows an entity to measure the fair value of financial instruments that are managed on the basis of the entity's net exposure to a particular market risk, or to the credit risk of a particular counterparty, on a net basis when certain criteria are met. Such criteria include that there is evidence that the entity manages its financial instruments in that way, the entity applies such accounting policy election consistently from period to period, and the entity is required or has elected to measure those financial assets and financial liabilities at fair value in the statement of financial position at the end of each reporting period. Additionally, to qualify for the exception to the valuation premise, the market risks that are being offset must be substantially the same. ASU 2011-04 also extends ASC 820's prohibition on the use of blockage factors in fair value measurements to all three levels of the fair value hierarchy except for fair value measurements of Level 2 and 3 measurements when market participants would incorporate the premium or discount into the measurement at the level of the unit of account specified in other guidance. ASU 2011-04 also provides that an entity should measure the fair value of its own equity instruments from the perspective of a market participant that holds the instruments as assets. Under ASC 820, as amended, expanded disclosures are required including disclosure of quantitative information about significant unobservable inputs used in Level 3 fair value measurements, a description of the valuation processes used by the entity, and a qualitative discussion about the sensitivity of the measurements. Additional disclosures required under ASU 2011-04 include disclosure of fair value by level for each class of assets and liabilities not recorded at fair value but for which fair value is disclosed, and disclosure of any transfers between Level 1 and Level 2 of the fair value hierarchy and the reasons for those transfers. The provisions of ASU 2011-04 are effective for periods beginning after December 15, 2011, with disclosure of the change, if any, in valuation technique and related inputs resulting from application of the amendments to ASC 820 required upon adoption, along with quantification of the total effect of the change, if practicable. FHN is currently assessing the effects of adopting the provisions of ASU 2011-04.

In April 2011, the FASB issued Accounting Standards Update 2011-03, "Reconsideration of Effective Control for Repurchase Agreements" ("ASU 2011-03"). For entities that enter into agreements to transfer financial assets that both entitle and obligate the transferor to repurchase or redeem the financial assets before their maturity, ASU 2011-03 removes from the assessment of effective control under ASC 860, "Transfers and Servicing", 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, as well as the collateral maintenance implementation guidance related to that criterion. Under ASC 860-10, as amended, the remaining criteria related to whether effective control over transferred financial assets has been maintained would still need to be evaluated, including whether the financial assets to be repurchased or redeemed are the same or substantially the same as those transferred, the agreement is to repurchase or redeem them before maturity at a fixed or determinable price, and whether the agreement is entered into contemporaneously with, or in contemplation of, the transfer. The provisions of ASU 2011-03 are effective for periods beginning after December 15, 2011, with prospective application to transactions or modifications of existing transactions that occur on or after the effective date. Since FHN accounts for all of its repurchase agreements as secured borrowings, adopting the provisions of ASU 2011-03 will not have an effect on FHN's statement of condition, results of operations, or cash flows.