Earnings Per Common Share - Calculation of EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic Earnings Per Common Share:
Net income attributable to TCF Financial Corporation	$ 55,738	$ 22,148	$ 131,401	$ 183,069
Preferred stock dividends	2,494	2,494	7,481	7,481
Net income available to common stockholders	53,244	19,654	123,920	175,588
Less: Earnings allocated to participating securities	0	0	0	19
Earnings allocated to common stock	$ 53,244	$ 19,654	$ 123,920	$ 175,569
Weighted-average common shares outstanding used in basic earnings per common share calculation (in shares)	151,768,337	128,575,171	151,761,299	97,876,262
Basic earnings per common share (in usd per share)	$ 0.35	$ 0.15	$ 0.82	$ 1.79
Diluted Earnings Per Common Share:
Earnings allocated to common stock	$ 53,244	$ 19,654	$ 123,920	$ 175,569
Weighted-average common shares outstanding used in basic earnings per common share calculation (in shares)	151,768,337	128,575,171	151,761,299	97,876,262
Net dilutive effect of:
Non-participating restricted stock (in shares)	26,163	73,698	12,383	139,795
Stock options (in shares)	27,092	105,719	53,246	39,222
Weighted-average common shares outstanding used in diluted earnings per common share calculation (in shares)	151,821,592	128,754,588	151,826,928	98,055,279
Diluted earnings per common share (in usd per share)	$ 0.35	$ 0.15	$ 0.82	$ 1.79
Non-participating restricted stock
Anti-dilutive shares outstanding not included in the computation of diluted earnings per share:
Non-participating restricted stock (in shares)	2,303,249	1,271,045	2,531,355	1,271,045
Stock options
Anti-dilutive shares outstanding not included in the computation of diluted earnings per share:
Non-participating restricted stock (in shares)	323,386	97,980	228,106	97,980