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Defined contribution plan, period of employment for eligibility.

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Minimum age for increase in per capita cost of health care benefit.

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

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

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Amount of plan asset for defined benefit pension plan with projected benefit obligation in excess of plan assets.

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Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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Ultimate trend rate for health care cost for defined benefit postretirement plan.

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

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Amount of cash outflow for pension benefit. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. Excludes other postretirement benefit.

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Retirement Benefit Plans (Narrative) (Details)	3 Months Ended	12 Months Ended
Retirement Benefit Plans (Narrative) (Details)	Mar. 31, 2019 USD ($)	Dec. 31, 2021 USD ($) Participant	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Apr. 30, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Contributed to pension plan	$ 100,000,000
Newly eligible associates initial savings rate		3.00%
Eligible participants under VERIP \| Participant		260
Pension plan assets					$ 808,000,000
Benefit obligation					$ 597,000,000
First 1% Of Contribution Saved [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching percentage		100.00%
Percentage of compensation saved		1.00%
Next 5% Of Contribution Saved [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching percentage		50.00%
Percentage of compensation saved		5.00%
Amended Hancock 401K Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional matching percentage		2.00%
Period of employment for eligibility		3 years
Amended Hancock 401K Plan [Member] \| 2% Of Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching percentage		2.00%
Amended Hancock 401K Plan [Member] \| 4% Of Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching percentage		4.00%
Amended Hancock 401K Plan [Member] \| 6% Of Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching percentage		6.00%
Whitney 401K Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		$ 16,600,000	$ 17,400,000	$ 15,700,000
Minimum age for increase in per capita cost of health care benefit		55 years
Years of credited service reaching 55 years of age		10 years
Hancock Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Minimum age for increase in per capita cost of health care benefit		55 years
Years of credited service reaching 55 years of age		10 years
Increase (decrease) in pre- and post-Medicare age health costs rate		6.25%
Period of assumed health rate decline		3 years
Decrease in ultimate rate over a period of time		5.50%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributed to pension plan		$ 0	0
Employer contributions		1,181,000	1,178,000
Funded status at end of year-net asset (liability)		213,051,000	$ 154,995,000
Excess of plan assets over the benefit obligation		228,100,000
Unfunded benefit obligation		$ 15,100,000