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Income Taxes - Additional Information (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Income Taxes [Line Items] |  |  |  |
Net capital loss carryforwards | $ 4,000,000 |  |  |
Valuation allowances | 5,000,000 | $ 15,000,000 |  |
Deferred tax asset | 1,854,000,000 | 2,437,000,000 |  |
Unrecognized tax benefits | 3,000,000 | 39,000,000 | $ 45,000,000 | $ 40,000,000
Net interest expense (benefit) | (16,000,000) | (1,000,000) | (4,000,000) |
Recovery of penalties related to unrecognized tax benefits in income tax expense | 0 | 0 | 0 |
Accrued interest payable | 1,000,000 | $ 1,000,000 | $ 600,000 |
Capital Loss Carryforward |  |  |  |
Income Taxes [Line Items] |  |  |  |
Valuation allowances | 4,000,000 |  |  |
First Niagara Bank, N.A. |  |  |  |
Income Taxes [Line Items] |  |  |  |
Allocated bad debt deductions for which no income taxes have been recorded | 92,000,000 |  |  |
Federal |  |  |  |
Income Taxes [Line Items] |  |  |  |
Operating loss carryforwards | 0 |  |  |
Credit carryforward | 226,000,000 |  |  |
Federal | General Business Tax Credit Carryforward |  |  |  |
Income Taxes [Line Items] |  |  |  |
Credit carryforward | 226,000,000 |  |  |
State |  |  |  |
Income Taxes [Line Items] |  |  |  |
Valuation allowances | 1,000,000 |  |  |
Operating loss carryforwards | 80,000,000 |  |  |
Credit carryforward | 2,000,000 |  |  |
Deferred tax asset | $ 3,000,000 |  |  |

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- Definition Unrecognized Tax Benefits Including Income Tax Penalties And Interest Accrued + References No definition available. + Details
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- Definition Unrecognized tax benefits, interest on income taxes expense benefit. + References No definition available. + Details
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible capital loss carryforwards. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-6 + Details
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- Definition Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-2 + Details
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-2 + Details
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- Definition Amount of deferred tax liability not recognized because of the exceptions to comprehensive recognition of deferred taxes related to bad debt reserve for tax purposes of a qualified lender. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 740 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477617/942-740-50-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 740 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478822/944-740-50-1 + Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-3 + Details
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- Definition The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-3 + Details
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