Defined Benefit and Other Postretirement Benefits - Weighted-Average Asset Allocation (Details) - Trustmark Capital Accumulation Plan [Member] - Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]	Dec. 31, 2023	Dec. 31, 2022
Asset target allocations [Abstract]
Weighted-average asset allocation (in hundredths)	100.00%	100.00%
Money Market Funds [Member]
Asset target allocations [Abstract]
Weighted-average asset allocation (in hundredths)	27.00%	7.00%
Exchange Traded Equity Securities Funds [Member]
Asset target allocations [Abstract]
Weighted-average asset allocation (in hundredths)	36.00%	47.00%
Exchange Traded Fixed Income Funds [Member]
Asset target allocations [Abstract]
Weighted-average asset allocation (in hundredths)	28.00%	39.00%
International Exchange Traded Funds [Member]
Asset target allocations [Abstract]
Weighted-average asset allocation (in hundredths)	9.00%	7.00%