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v3.19.1

Leases - Narrative (Details) $ in Millions | Mar. 31, 2019 USD ($)
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Leases [Abstract] |
Undiscounted amount of leases that have not yet commenced | $ 22.1

X
- Definition Lessee, Operating Lease, Lease Not yet Commenced, Undiscounted Amount + References No definition available. + Details
Name: | fhn_LesseeOperatingLeaseLeaseNotyetCommencedUndiscountedAmount
Namespace Prefix: | fhn_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_LeasesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration