CONSOLIDATED STATEMENTS OF EQUITY (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity, Class of Treasury Stock [Line Items]
Preferred stock - cash dividends declared per share (in dollars per share)		$ 6,200	$ 6,200
Common stock - cash dividends declared per share (in dollars per share)	$ 0.60	0.56	0.48
Cash dividends declared per common share (in dollars per share)	$ 0.60	$ 0.56	$ 0.48
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member	us-gaap:AccountingStandardsUpdate201802Member
Preferred Stock
Equity, Class of Treasury Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	1,500
Sale of stock (in dollars per share)	$ 100,000
First Horizon Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased under share repurchase programs	$ 4.0	$ 130.0	$ 99.0