Retirement Plans - Narrative (Details) - USD ($)	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Weighted-average interest crediting rate	2.05%
Discount rate	3.48%
Company contributions to defined benefit plans	$ 0	$ 0
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Company contributions to defined benefit plans	21,000	107,000
Chemical Financial Corporation
Defined Benefit Plan Disclosure [Line Items]
Company contributions to defined benefit plans	$ 0
401K Plan After January 1, 2016
Defined Benefit Plan Disclosure [Line Items]
Maximum percent of eligible compensation for 401k plan	50.00%
Employer matching contribution, per dollar	1
The TCF 401K Plan
Defined Benefit Plan Disclosure [Line Items]
Company contributions to 401k Plans	$ 6,500,000	$ 4,300,000
Maximum \| 401K Plan After January 1, 2016
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent	5.00%

Employer Matching Contribution Per Dollar

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

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- Definition

Weighted-average interest crediting rate used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.

+ References

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

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- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

No definition available.

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