Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic earnings per common share:
Net income attributable to TCF Financial Corporation	$ 91,358	$ 55,738	$ 23,764	$ 51,899	$ 112,399	$ 22,148	$ 90,427	$ 70,494	$ 222,759	$ 295,468	$ 304,358
Preferred stock dividends	$ 2,494	$ 2,494	$ 2,494	$ 2,493	$ 2,494	$ 2,494	$ 2,494	$ 2,493	9,975	9,975	11,588
Impact of preferred stock redemption									0	0	3,481
Net income available to common stockholders									212,784	285,493	289,289
Less: Earnings allocated to participating securities									0	20	42
Earnings allocated to common stock									$ 212,784	$ 285,473	$ 289,247
Weighted-average common shares outstanding used in basic earnings per common share calculation (in shares)									151,812,393	111,604,094	84,133,983
Basic earnings per common share (in dollars per share)	$ 0.58	$ 0.35	$ 0.14	$ 0.33	$ 0.72	$ 0.15	$ 1.07	$ 0.83	$ 1.40	$ 2.56	$ 3.44
Diluted earnings per common share:
Earnings allocated to common stock									$ 212,784	$ 285,473	$ 289,247
Weighted-average common shares outstanding used in basic earnings per common share calculation (in shares)									151,812,393	111,604,094	84,133,983
Net dilutive effect of:
Non-participating restricted stock (in shares)									23,901	140,832	0
Stock options (in shares)									51,265	73,439	1,184
Warrants (in shares)									0	0	189,519
Weighted-average common shares outstanding used in diluted earnings per common share calculation (in shares)									151,887,559	111,818,365	84,324,686
Diluted earnings per common share (in dollars per share)	$ 0.58	$ 0.35	$ 0.14	$ 0.32	$ 0.72	$ 0.15	$ 1.07	$ 0.83	$ 1.40	$ 2.55	$ 3.43
Non-Participating Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)									2,086,305	1,288,539	1,028,942
Stock Options Outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)									244,004	97,980	0