Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income
Interest and fees on loans and leases	$ 1,575,186	$ 1,430,628	$ 1,082,135
Interest on investment securities:
Taxable	144,462	106,027	41,406
Tax-exempt	16,168	11,651	17,138
Interest on loans held-for-sale	11,394	18,599	6,686
Interest on other earning assets	18,452	20,356	11,964
Total interest income	1,765,662	1,587,261	1,159,329
Interest expense
Interest on deposits	166,986	226,157	107,690
Interest on borrowings	60,275	72,072	43,144
Total interest expense	227,261	298,229	150,834
Net interest income	1,538,401	1,289,032	1,008,495
Provision for credit losses	257,151	65,282	46,768
Net interest income after provision for credit losses	1,281,250	1,223,750	961,727
Noninterest income
Net gains on sales of loans and leases	86,776	26,308	33,695
Net gains on investment securities	2,338	7,425	348
Other	46,542	21,811	28,769
Total noninterest income	516,063	465,532	454,397
Noninterest expense
Compensation and employee benefits	702,702	576,922	502,196
Occupancy and equipment	209,690	189,560	165,839
Lease financing equipment depreciation	73,204	76,426	73,829
Net foreclosed real estate and repossessed assets	5,136	13,523	17,050
Merger-related expenses	203,888	171,968	0
Other	332,751	303,716	255,486
Total noninterest expense	1,527,371	1,332,115	1,014,400
Income before income tax expense	269,942	357,167	401,724
Income tax expense	39,901	50,241	86,096
Income after income tax expense	230,041	306,926	315,628
Income attributable to non-controlling interest	7,282	11,458	11,270
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
Earnings per common share
Basic (in usd per share)	$ 1.40	$ 2.56	$ 3.44
Diluted (in usd per share)	$ 1.40	$ 2.55	$ 3.43
Weighted-average common shares outstanding
Basic (in shares)	151,812,393	111,604,094	84,133,983
Diluted (in shares)	151,887,559	111,818,365	84,324,686
Leasing revenue
Noninterest income
Noninterest income	$ 142,723	$ 163,718	$ 172,603
Fees and service charges on deposit accounts
Noninterest income
Noninterest income	112,681	127,860	113,242
Total noninterest income	112,681	127,860	113,242
Card and ATM revenue
Noninterest income
Noninterest income	88,699	87,221	78,406
Total noninterest income	88,699	87,221	78,406
Wealth management revenue
Noninterest income
Noninterest income	25,701	10,413	0
Total noninterest income	25,701	10,413
Servicing fee revenue
Noninterest income
Noninterest income	$ 10,603	$ 20,776	$ 27,334