Allowance for Credit Losses - Rollforward of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 815	$ 773
Charge-offs	(41)	(46)
Recoveries	12	6
Provision for loan and lease losses	36	54
Ending balance	822	787
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	79	83
Provision for remaining unfunded commitments	4	(4)
Ending balance	83	79
Allowance for credit losses	905	866
Commercial: \| Commercial, financial, and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	345	339
Charge-offs	(34)	(28)
Recoveries	6	3
Provision for loan and lease losses	28	34
Ending balance	345	348
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	57	49
Provision for remaining unfunded commitments	6	0
Ending balance	63	49
Allowance for credit losses	408	397
Commercial: \| Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	227	172
Charge-offs	(3)	(12)
Recoveries	4	0
Provision for loan and lease losses	(3)	21
Ending balance	225	181
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	11	22
Provision for remaining unfunded commitments	(2)	(4)
Ending balance	9	18
Allowance for credit losses	234	199
Consumer: \| Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	221	233
Charge-offs	0	0
Recoveries	1	1
Provision for loan and lease losses	8	(3)
Ending balance	230	231
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	11	12
Provision for remaining unfunded commitments	0	0
Ending balance	11	12
Allowance for credit losses	241	243
Consumer: \| Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	22	29
Charge-offs	(4)	(6)
Recoveries	1	2
Provision for loan and lease losses	3	2
Ending balance	22	27
Off-Balance-Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	0	0
Provision for remaining unfunded commitments	0	0
Ending balance	0	0
Allowance for credit losses	$ 22	$ 27

Financing Receivable And Off-Balance Sheet Credit Loss Liability, Allowance For Credit Loss, Excluding Accrued Interest

No definition available.

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Namespace Prefix:	fhn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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Balance Type:	debit
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- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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Balance Type:	debit
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- Definition

Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482454/460-10-45-1

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of expense (reversal of expense) for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

+ Details

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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