Business Segment Information - Schedule of Amounts of Consolidated Revenue, Expense, Tax and Assets by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Interest income	$ 4,352	$ 4,100	$ 2,683
Interest expense	1,841	1,560	291
Funds transfer pricing	0	0	0
Net interest income	2,511	2,540	2,392
Noninterest income	679	927	815
Total revenues	3,190	3,467	3,207
Noninterest expense	2,035	2,079	1,953
Pre-provision net revenue	1,155	1,388	1,254
Provision for credit losses	150	260	95
Income before income taxes	1,005	1,128	1,159
Income tax expense (benefit)	211	212	247
Net income (loss)	794	916	912
Average assets	81,822	81,683	84,217
Depreciation and amortization	101	102	85
Expenditures for long-lived assets	45	34	24
Gain on merger termination	0	225	0
Gain on divestiture	0	9	0
Visa Class B Shares
Segment Reporting Information [Line Items]
Derivative valuation adjustment	15	15
Commercial, Consumer & Wealth
Segment Reporting Information [Line Items]
Interest income	3,538	3,286	2,053
Interest expense	1,413	1,115	156
Funds transfer pricing	418	523	368
Net interest income	2,543	2,694	2,265
Noninterest income	461	448	477
Total revenues	3,004	3,142	2,742
Noninterest expense	1,417	1,370	1,309
Pre-provision net revenue	1,587	1,772	1,433
Provision for credit losses	158	260	85
Income before income taxes	1,429	1,512	1,348
Income tax expense (benefit)	337	357	319
Net income (loss)	1,092	1,155	1,029
Average assets	59,402	58,126	52,771
Depreciation and amortization	37	34	(1)
Expenditures for long-lived assets	26	16	15
Gain on merger termination		0
Wholesale
Segment Reporting Information [Line Items]
Interest income	530	478	339
Interest expense	125	100	47
Funds transfer pricing	(211)	(195)	(39)
Net interest income	194	183	253
Noninterest income	230	174	259
Total revenues	424	357	512
Noninterest expense	299	276	344
Pre-provision net revenue	125	81	168
Provision for credit losses	3	15	11
Income before income taxes	122	66	157
Income tax expense (benefit)	29	16	38
Net income (loss)	93	50	119
Average assets	8,209	7,583	9,172
Depreciation and amortization	7	7	6
Expenditures for long-lived assets	1	1	10
Gain on merger termination		0
Gain on sale of mortgage servicing rights			12
Wholesale | FHN Financial Securities Corp.
Segment Reporting Information [Line Items]
Gain on disposition of assets		9
Corporate
Segment Reporting Information [Line Items]
Interest income	284	336	291
Interest expense	303	345	88
Funds transfer pricing	(207)	(328)	(329)
Net interest income	(226)	(337)	(126)
Noninterest income	(12)	305	79
Total revenues	(238)	(32)	(47)
Noninterest expense	319	433	300
Pre-provision net revenue	(557)	(465)	(347)
Provision for credit losses	(11)	(15)	(1)
Income before income taxes	(546)	(450)	(346)
Income tax expense (benefit)	(155)	(161)	(110)
Net income (loss)	(391)	(289)	(236)
Average assets	14,211	15,974	22,274
Depreciation and amortization	57	61	80
Expenditures for long-lived assets	18	17	(1)
Gain on merger termination		225
Equity securities losses		6	(10)
Restructuring costs	14	10
FDIC special assessment	9	68
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	15	22
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 | Title Insurance Business
Segment Reporting Information [Line Items]
Gain on divestiture			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
Corporate | Other Restructuring
Segment Reporting Information [Line Items]
Loss on securities	$ 91