Cover - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2020	Apr. 19, 2021
Document Information [Line Items]
Document Type	10-K/A
Amendment Description	We filed our Annual Report on Form 10-K for the fiscal year ended December 31, 2020 (“Form 10-K”) with the U.S. Securities and Exchange Commission (“SEC”) on February 26, 2021. We are filing this Amendment No. 1 (the “Amendment”) on Form 10-K/A to amend the Form 10-K solely for the purpose of including in Part III the information that was to be incorporated by reference from our definitive proxy statement for the 2021 annual meeting of shareholders, because our definitive proxy statement will not be filed with the SEC within 120 days after the end of our fiscal year ended December 31, 2020. This Amendment hereby amends and restates in their entirety the Form 10-K cover page and Items 10 through 14 of Part III.Pursuant to Rule 12b-15 under the Securities Exchange Act of 1934, as amended, this Form 10-K/A also contains new certifications by the principal executive officer and the principal financial officer as required by Section 302 of the Sarbanes-Oxley Act of 2002. Accordingly, Item 15(a)(3) of Part IV is amended to include the currently dated certifications as exhibits. Because no financial statements have been included in this Amendment and this Amendment does not contain or amend any disclosure with respect to Items 307 and 308 of Regulation S-K, paragraphs 3, 4 and 5 of the certifications have been omitted.Except as expressly noted in this Amendment, this Amendment does not reflect events occurring after the original filing of our Form 10-K or modify or update in any way any of the other disclosures contained in our Form 10-K including, without limitation, the financial statements. Accordingly, this Amendment should be read in conjunction with our Form 10-K and our other filings with the SEC.
Document Period End Date	Dec. 31, 2020
Document Annual Report	true
Document Transition Report	false
Entity File Number	001-39009
Entity Registrant Name	TCF Financial Corporation
Entity Incorporation, State or Country Code	MI
Entity Tax Identification Number	38-2022454
Entity Address, Address Line One	333 W. Fort Street, Suite 1800
Entity Address, City or Town	Detroit
Entity Address, State or Province	MI
Entity Address, Postal Zip Code	48226
City Area Code	(866)
Local Phone Number	258-1807
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float	$ 4.3
Entity Common Stock, Shares Outstanding		152,650,970
Entity Central Index Key	0000019612
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	true
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock (par value $1 per share)
Trading Symbol	TCF
Security Exchange Name	NASDAQ
Depositary Shares
Document Information [Line Items]
Title of 12(b) Security	Depositary shares, each representing a 1/1000th interest in a share of the 5.70% Series C Non-Cumulative Perpetual Preferred Stock
Trading Symbol	TCFCP
Security Exchange Name	NASDAQ