Merger - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Aug. 01, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Common stock, shares outstanding (in shares)	153,500,000
Preferred stock, shares outstanding (in shares)		7,000	7,000
Other intangible assets	$ 159,532
Estimated useful life	11 years
Goodwill	$ 1,145,121	$ 1,299,878	$ 154,757
Core deposit intangibles
Business Acquisition [Line Items]
Other intangible assets	$ 138,200
Estimated useful life	10 years
Customer relationships
Business Acquisition [Line Items]
Other intangible assets	$ 21,300
Estimated useful life	15 years 7 months 6 days
Legacy TCF
Business Acquisition [Line Items]
Common stock, shares outstanding (in shares)	302,065,045
Chemical Financial Corporation
Business Acquisition [Line Items]
Common stock, shares outstanding (in shares)	153,479,249
TCF Financial Corporation
Business Acquisition [Line Items]
Voting interest percent	53.00%
Common Stock
Business Acquisition [Line Items]
Share conversion ratio (in shares)	0.5081
Shares issued in acquisition (in shares)	81,900,000
Series C Preferred Stock
Business Acquisition [Line Items]
Dividend rate on preferred stock	5.70%	5.70%	5.70%	5.70%
Liquidation preference (in usd per share)	$ 25,000		$ 25,000
Series C Preferred Stock | Legacy TCF
Business Acquisition [Line Items]
Dividend rate on preferred stock	5.70%
Liquidation preference (in usd per share)	$ 25,000
New Chemical Preferred Stock | Chemical Financial Corporation
Business Acquisition [Line Items]
Share conversion ratio (in shares)	1
Dividend rate on preferred stock	5.70%
Liquidation preference (in usd per share)	$ 25,000
Preferred stock, shares outstanding (in shares)	7,000
Depositary Shares | Chemical Financial Corporation
Business Acquisition [Line Items]
Preferred stock, shares outstanding (in shares)	7,000,000.0
Consumer Banking
Business Acquisition [Line Items]
Goodwill	$ 522,000	$ 764,389	$ 141,246
Commercial Banking
Business Acquisition [Line Items]
Goodwill	$ 623,100