Parent Company Financial Information - Condensed Statements of Income (Details) - USD ($) $ 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
Interest income:
Interest expense									$ 227,261	$ 298,229	$ 150,834
Net interest income	$ 381,394	$ 377,167	$ 378,359	$ 401,481	$ 408,753	$ 371,793	$ 254,057	$ 254,429	1,538,401	1,289,032	1,008,495
Non-interest income:
Total noninterest income	127,236	118,810	133,054	136,963	158,052	94,258	109,718	103,504	516,063	465,532	454,397
Non-interest expense:
Compensation and employee benefits									702,702	576,922	502,196
Occupancy and equipment									209,690	189,560	165,839
Merger-related expenses									203,888	171,968	0
Other									332,751	303,716	255,486
Noninterest expense	379,091	373,440	400,241	374,599	416,571	425,620	236,849	253,075	1,527,371	1,332,115	1,014,400
Income before income tax expense	117,721	52,873	32,446	66,902	135,831	13,243	113,357	94,736	269,942	357,167	401,724
Income tax benefit	(25,031)	4,429	(6,213)	(13,086)	(21,375)	11,735	(19,314)	(21,287)	(39,901)	(50,241)	(86,096)
Equity in undistributed earnings (loss) of TCF Bank									212,784	285,493	289,289
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
Impact of preferred stock redemption											3,481
Net income available to common shareholders	$ 88,864	$ 53,244	$ 21,270	$ 49,406	$ 109,905	$ 19,654	$ 87,933	$ 68,001	212,784	285,493	289,289
TCF Financial Corporation
Interest income:
Interest income:									436	262	200
Interest expense									1,318	484	0
Net interest income									(882)	(222)	200
Non-interest income:
Dividends from TCF Bank									245,000	225,000	431,000
Management fees									53,318	14,001	20,532
Other									2,655	581	426
Total noninterest income									300,973	239,582	451,958
Non-interest expense:
Compensation and employee benefits									45,507	18,677	20,282
Occupancy and equipment									532	470	301
Merger-related expenses									30,273	69,944	0
Other									4,309	5,040	5,682
Noninterest expense									80,621	94,131	26,265
Income before income tax expense									219,470	145,229	425,893
Income tax benefit									5,961	15,513	952
Income before equity in undistributed earnings (loss) of TCF Bank									225,431	160,742	426,845
Equity in undistributed earnings (loss) of TCF Bank									(2,672)	134,726	(122,487)
Net income attributable to TCF Financial Corporation									222,759	295,468	304,358
Preferred stock dividends									9,975	9,975	11,588
Impact of preferred stock redemption									0	0	3,481
Net income available to common shareholders									$ 212,784	$ 285,493	$ 289,289