Financial Information (Policy)	3 Months Ended
Mar. 31, 2012
Financial Information [Abstract]
Basis Of Accounting	*Basis of Accounting.* 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 2012 period 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 2011 Annual Report to shareholders.
New Accounting Pronouncement Or Change In Accounting Principle Policy	*Summary of Accounting Changes. Effective January 1, 2012, 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 previously 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 had no effect on FHN's statement of condition, results of operations, or cash flows. Effective January 1, 2012, 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. No transition disclosures are required upon adoption. For interim reporting periods, filers are only required to present total comprehensive income in a single continuous statement or in two consecutive statements. On December 23, 2011, the FASB issued ASU 2011-12, which indefinitely defers the provisions of ASU 2011-05 that require entities to present reclassification adjustments out of accumulated other comprehensive income by component in both the statement in which net income is presented and the statement in which other comprehensive income is presented (for both interim and annual financial statements). Upon adoption of the provisions of ASU 2011-05 and ASU 2011-12 on January 1, 2012, FHN revised its financial statements and disclosures accordingly. Effective January 1, 2012, 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, 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 recurring Level 3 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. Upon adoption of the provisions of ASU 2011-04, FHN revised its disclosures accordingly. Adoption of ASU 2011-04 had no effect on FHN's statement of condition, results of operations, or cash flows. Effective January 1, 2012, 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 did not have an effect on FHN's statement of condition, results of operations, or cash flows. Accounting Changes Issued but Not Currently Effective.* In December 2011, the FASB issued Accounting Standards Update 2011-11, "Balance Sheet: Disclosures about Offsetting Assets and Liabilities" ("ASU 2011-11"). ASU 2011-11 creates new disclosure requirements about the nature of an entity's rights of setoff and related arrangements associated with its financial instruments and derivative instruments. ASU 2011-11 requires entities to disclose both gross and net information about both instruments/transactions eligible for offset in the balance sheet and instruments/transactions subject to an agreement similar to a master netting arrangement. The scope of ASU 2011-11 includes derivatives, sale and repurchase agreements/reverse sale and repurchase agreements, and securities borrowing and securities lending arrangements. The provisions of ASU 2011-11 are effective for periods beginning after January 1, 2013, with retrospective application to all periods presented in the financial statements required. FHN is currently assessing the effects of adopting the provisions of ASU 2011-11.

Summary of Accounting Changes. Effective January 1, 2012, 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 previously 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 had no effect on FHN's statement of condition, results of operations, or cash flows.

Effective January 1, 2012, 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. No transition disclosures are required upon adoption. For interim reporting periods, filers are only required to present total comprehensive income in a single continuous statement or in two consecutive statements. On December 23, 2011, the FASB issued ASU 2011-12, which indefinitely defers the provisions of ASU 2011-05 that require entities to present reclassification adjustments out of accumulated other comprehensive income by component in both the statement in which net income is presented and the statement in which other comprehensive income is presented (for both interim and annual financial statements). Upon adoption of the provisions of ASU 2011-05 and ASU 2011-12 on January 1, 2012, FHN revised its financial statements and disclosures accordingly.

Effective January 1, 2012, 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, 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 recurring Level 3 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. Upon adoption of the provisions of ASU 2011-04, FHN revised its disclosures accordingly. Adoption of ASU 2011-04 had no effect on FHN's statement of condition, results of operations, or cash flows.

Effective January 1, 2012, 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 did not have an effect on FHN's statement of condition, results of operations, or cash flows.

Accounting Changes Issued but Not Currently Effective. In December 2011, the FASB issued Accounting Standards Update 2011-11, "Balance Sheet: Disclosures about Offsetting Assets and Liabilities" ("ASU 2011-11"). ASU 2011-11 creates new disclosure requirements about the nature of an entity's rights of setoff and related arrangements associated with its financial instruments and derivative instruments. ASU 2011-11 requires entities to disclose both gross and net information about both instruments/transactions eligible for offset in the balance sheet and instruments/transactions subject to an agreement similar to a master netting arrangement. The scope of ASU 2011-11 includes derivatives, sale and repurchase agreements/reverse sale and repurchase agreements, and securities borrowing and securities lending arrangements. The provisions of ASU 2011-11 are effective for periods beginning after January 1, 2013, with retrospective application to all periods presented in the financial statements required. FHN is currently assessing the effects of adopting the provisions of ASU 2011-11.