CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Parenthetical) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Sep. 30, 2025		Jun. 30, 2025		Mar. 31, 2025		Sep. 30, 2024		Jun. 30, 2024		Mar. 31, 2024		Dec. 31, 2023
Common stock - cash dividends declared per share (in dollars per share)	$ 0.15		$ 0.15		$ 0.15		$ 0.15		$ 0.15		$ 0.15
Common stock repurchased under share repurchase program	$ 191	[1]	$ 27	[1]	$ 365	[1]	$ 75	[2]	$ 228	[2]	$ 159	[2]
Accounting Standards Update [Extensible List]													Accounting Standards Update 2023-02 [Member]
General Purchase Plan
Common stock repurchased under share repurchase program	190		$ 9		$ 360		75		$ 212		$ 154
Share repurchase program, authorized, amount	$ 1,000						$ 650

[1] Includes $360 million, $9 million, and $190 million repurchased during first, second, and third quarter, respectively, under FHN's $1 billion general purchase program approved in October 2024

[2] Includes $154 million, $212 million, and $75 million repurchased during first, second, and third quarter, respectively, under FHN's $650 million general purchase program approved in January 2024 and terminated in October 2024.