Business Segment Information - Schedule of Amounts of Consolidated Revenue, Expense, Tax and Assets by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 2,540	$ 2,392	$ 1,994
Provision (benefit) for credit losses	260	95	(310)
Noninterest income	927	815	1,076
Noninterest expense	2,079	1,953	2,096
Income before income taxes	1,128	1,159	1,284
Income tax expense (benefit)	212	247	274
Net income (loss)	916	912	1,010
Average assets	81,683	84,217	87,609
Depreciation and amortization	102	85	45
Expenditures for long-lived assets	34	24	37
Gain on merger termination	225	0	0
Gain on sale of title services business	9	0	0
Visa Class B Shares
Segment Reporting Information [Line Items]
Derivative valuation adjustment	15	22
Regional Banking
Segment Reporting Information [Line Items]
Net interest income (expense)	2,354	1,954	1,764
Provision (benefit) for credit losses	224	94	(229)
Noninterest income	433	443	438
Noninterest expense	1,301	1,226	1,136
Income before income taxes	1,262	1,077	1,295
Income tax expense (benefit)	296	253	303
Net income (loss)	966	824	992
Average assets	45,858	42,297	41,527
Depreciation and amortization	60	24	(57)
Expenditures for long-lived assets	29	18	27
Gain on merger termination	0
Specialty Banking
Segment Reporting Information [Line Items]
Net interest income (expense)	518	557	620
Provision (benefit) for credit losses	50	14	(64)
Noninterest income	209	312	597
Noninterest expense	364	446	573
Income before income taxes	313	409	708
Income tax expense (benefit)	76	99	172
Net income (loss)	237	310	536
Average assets	20,161	19,965	20,789
Depreciation and amortization	0	2	4
Expenditures for long-lived assets	4	12	3
Gain on merger termination	0
Specialty Banking | FHN Financial Securities Corp.
Segment Reporting Information [Line Items]
Gain on disposition of assets	7
Corporate
Segment Reporting Information [Line Items]
Net interest income (expense)	(332)	(119)	(390)
Provision (benefit) for credit losses	(14)	(13)	(17)
Noninterest income	285	60	41
Noninterest expense	414	281	387
Income before income taxes	(447)	(327)	(719)
Income tax expense (benefit)	(160)	(105)	(201)
Net income (loss)	(287)	(222)	(518)
Average assets	15,664	21,955	25,293
Depreciation and amortization	42	59	98
Expenditures for long-lived assets	1	(6)	7
Gain on merger termination	225
Equity securities losses	6
Gain on sale of mortgage servicing rights		12
Gain on sale of title services business		10
Restructuring Costs	10
FDIC special assessment	68
Long-lived asset impairment			37
Surrender of bank owned life insurance	24
Benefit from merger-related tax items	59
Corporate | Visa Class B Shares
Segment Reporting Information [Line Items]
Derivative valuation adjustment	15	22	19
Corporate | Fintech Investment
Segment Reporting Information [Line Items]
Gain on sale of investments		6
Corporate | First Horizon Foundation
Segment Reporting Information [Line Items]
Charitable foundation contributions	50
Corporate | Insurance Business
Segment Reporting Information [Line Items]
Gain on sale of title services business		22
Corporate | TD Transaction
Segment Reporting Information [Line Items]
Gain on merger termination	225
Merger and integration expense	$ 51
Corporate | BKC Merger and TD Merger Agreement
Segment Reporting Information [Line Items]
Merger and integration expense		$ 136	187
Corporate | TRUPS
Segment Reporting Information [Line Items]
Loss on redemption in corporate segment			$ 26