CAPITAL ISSUANCES (Details) - $ / shares		12 Months Ended
	Jun. 26, 2020	Dec. 31, 2020	Dec. 31, 2019	Jan. 17, 2012
Class of Stock [Line Items]
Issuance of shares of Series E preferred stock (in shares)		11,500
Liquidation value per share (in dollars per share)				$ 1,000
Depositary Shares, each representing 1/400th interest in a share of 7.00% Fixed-Rate Reset Non-Cumulative Perpetual Preferred Stock, Series E
Class of Stock [Line Items]
Issuance of shares of Series E preferred stock (in shares)	4,600,000
Liquidation value per share (in dollars per share)	$ 25
Depositary Shares, each representing 1/400th interest in a share of 7.00% Fixed-Rate Reset Non-Cumulative Perpetual Preferred Stock, Series E | Heartland Financial
Class of Stock [Line Items]
Ownership percentage	0.25%
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividend rate	7.00%
Preferred stock, par value (in dollars per share)		$ 1	$ 1
Liquidation value per share (in dollars per share)	$ 10,000