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Retirement Benefit Plans - Weighted Average Assumptions used to Determine Net Periodic Benefit Cost (Details) | 12 Months Ended |  |
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2034 | Dec. 31, 2033
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Expected Long-Term Rate of Return on Plan Assets | 6.00% |  |  |  |
Forecast |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Cost trend rate |  |  |  | 4.40% | 4.40%
Pension | Webster Bank Pension Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.76% | 4.96% | 2.65% |  |
Expected Long-Term Rate of Return on Plan Assets | 6.00% | 6.00% | 5.50% |  |
SERP | Webster Bank Supplemental Defined Benefit Plan for Executive Officers |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.68% | 4.88% | 2.45% |  |
SERP | Astoria Bank Excess Benefit and Supplemental Benefit Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.56% | 4.77% | 2.58% |  |
SERP | Astoria Bank Directors’ Retirement Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.50% | 4.70% | 2.23% |  |
SERP | Retirement Plan of the Greater New York Savings Bank for Non-Employee Directors |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.50% | 4.70% | 2.37% |  |
SERP | Supplemental Executive Retirement Plan of Provident Bank |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.83% | 5.04% | 2.76% |  |
SERP | Supplemental Executive Retirement Plan of Provident Bank - Other |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.71% | 4.90% | 2.38% |  |
OPEB | Webster Bank Postretirement Medical Benefit Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.54% | 4.72% | 1.99% |  |
Assumed Healthcare Cost Trend Rate | 6.50% | 6.50% | 6.25% |  |
OPEB | Sterling Bancorp Supplemental Postretirement Life Insurance Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.51% | 4.70% | 2.35% |  |
OPEB | Astoria Bank Postretirement Welfare Benefit Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.74% | 4.94% | 2.93% |  |
Assumed Healthcare Cost Trend Rate | 6.50% | 6.40% | 6.60% |  |
OPEB | Split Dollar Life Insurance Arrangement |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Discount Rate | 4.45% | 4.63% | 2.20% |  |

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-8 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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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. + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (l) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Ultimate trend rate for health care cost for defined benefit postretirement plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (l) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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