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Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring, Recorded Investment | $ 184,000,000 |  | $ 184,000,000 |  | $ 132,000,000
Financing Receivable, Troubled Debt Restructuring, Performing in Accordance With Modified Terms | 65,000,000 |  | 65,000,000 |  | 57,000,000
Financing Receivable, Troubled Debt Restructuring, Postmodification | 36,000,000 | $ 6,200,000 | 76,000,000 | $ 40,000,000 |
Financing Receivable, Impaired, Troubled Debt Restructuring, Write-down | 6,400,000 | $ 2,500,000 | 16,100,000 | $ 15,100,000 |
Residential mortgage [Member] | Loans to individuals [Member] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring, Specific Allowance | 0 |  | 0 |  |
Residential mortgage [Member] | Nonperforming Financial Instruments [Member] | Loans to individuals [Member] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring, Recorded Investment | 19,000,000 |  | 19,000,000 |  |
Energy [Member] | Commercial [Member] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring, Specific Allowance | 2,000,000.0 |  | 2,000,000.0 |  |
Energy [Member] | Nonperforming Financial Instruments [Member] | Commercial [Member] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring, Recorded Investment | 11,000,000 |  | 11,000,000 |  |
US Government Agency Insured Loans [Member] | Residential mortgage [Member] | Performing [Member] | Loans to individuals [Member] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring, Recorded Investment | $ 143,000,000 |  | $ 143,000,000 |  | $ 92,000,000

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- Definition Represents the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructuring and are performing according to modified terms. + References No definition available. + Details
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