Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Aug. 01, 2019	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2019
Preferred Stock Information
Preferred stock, par value (in dollars per share)		$ 0.01		$ 0.01
Series C non-cumulative perpetual preferred stock
Preferred Stock Information
Preferred stock, value outstanding		$ 169,302		$ 169,302
Dividends on preferred stock		5.70%	5.70%
Preferred stock, par value (in dollars per share)		$ 0.01
Preferred stock, liquidation preference per share (in dollars per share)		25,000
Preferred stock, liquidation preference per depositary share (in dollars per share)		$ 25
Preferred stock, depositary shares outstanding (in shares)		7,000,000
TCF Financial Corporation | Preferred Stock
Preferred Stock Information
Dividends on preferred stock	5.70%
Preferred stock, liquidation preference per share (in dollars per share)	$ 25,000
Preferred stock, shares outstanding (in shares)		7,000