Allowance for Credit Losses and Credit Quality - Rollfowards of the Allowance for Loan and Lease Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Allowance for loan and lease losses [Roll Forward]
Balance, beginning of period	$ 525,868	$ 113,052
Charge-offs	(55,618)	(14,729)
Recoveries	12,356	9,252
Net (charge-offs) recoveries	(43,262)	(5,477)
Provision for credit losses	21,960	92,990
Other	79	(174)
Balance, end of period	504,645	406,383
Unfunded commitments [Roll Forward]
Balance, beginning of period	23,313	3,528
Charge-offs	0	0
Recoveries	0	0
Net (charge-offs) recoveries	0	0
Provision for credit losses	(1,404)	3,953
Other	0	0
Balance, end of period	21,909	22,188
Allowance for loan, leases and unfunded commitments [Roll Forward]
Balance, beginning of period	549,181	116,580
Charge-offs	(55,618)	(14,729)
Recoveries	12,356	9,252
Net (charge-offs) recoveries	(43,262)	(5,477)
Provision for credit losses	20,556	96,943
Other	79	(174)
Balance, end of period	526,554	428,571
Consumer
Allowance for loan and lease losses [Roll Forward]
Balance, beginning of period	136,894	28,572
Charge-offs	(8,340)	(5,848)
Recoveries	7,879	4,708
Net (charge-offs) recoveries	(461)	(1,140)
Provision for credit losses	9,276	40,288
Other	(2,230)	0
Balance, end of period	143,479	175,057
Commercial
Allowance for loan and lease losses [Roll Forward]
Balance, beginning of period	388,974	84,480
Charge-offs	(47,278)	(8,881)
Recoveries	4,477	4,544
Net (charge-offs) recoveries	(42,801)	(4,337)
Provision for credit losses	12,684	52,702
Other	2,309	(174)
Balance, end of period	$ 361,166	231,326
Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan and lease losses [Roll Forward]
Balance, beginning of period		205,992
Unfunded commitments [Roll Forward]
Balance, beginning of period		14,707
Allowance for loan, leases and unfunded commitments [Roll Forward]
Balance, beginning of period		220,699
Cumulative Effect, Period of Adoption, Adjustment \| Consumer
Allowance for loan and lease losses [Roll Forward]
Balance, beginning of period		107,337
Cumulative Effect, Period of Adoption, Adjustment \| Commercial
Allowance for loan and lease losses [Roll Forward]
Balance, beginning of period		98,655
Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan and lease losses [Roll Forward]
Balance, beginning of period		319,044
Unfunded commitments [Roll Forward]
Balance, beginning of period		18,235
Allowance for loan, leases and unfunded commitments [Roll Forward]
Balance, beginning of period		337,279
Cumulative Effect, Period of Adoption, Adjusted Balance \| Consumer
Allowance for loan and lease losses [Roll Forward]
Balance, beginning of period		135,909
Cumulative Effect, Period of Adoption, Adjusted Balance \| Commercial
Allowance for loan and lease losses [Roll Forward]
Balance, beginning of period		$ 183,135

TCF FINANCIAL CORP 10-Q