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Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Commercial Real Estate Exposure) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Total loans | $ 52,113 | $ 53,402 |
Loans, average | $ 53,903 | 50,460 | $ 49,083
Concentration risk threshold - Auto | 14.00% |  |
Real estate construction loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Total loans | $ 5,083 | 3,105 |
Commercial mortgage loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Total loans | 13,686 | 13,306 |
Total commercial real estate |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Total loans | 18,769 | 16,411 |
Total unused commitments | 4,382 | 6,602 |
Commercial Real Estate business line | Real estate construction loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Total loans | 4,570 | 2,505 |
Commercial Real Estate business line | Commercial mortgage loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Total loans | 4,727 | 4,681 |
Other Business Lines Member | Real estate construction loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Total loans | 513 | 600 |
Other Business Lines Member | Commercial mortgage loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Total loans | $ 8,959 | $ 8,625 |

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- Definition Reflects the average aggregate gross carrying amount of all categories of loans and leases held in portfolio, after deducting deferred income, but before deducting the allowance for losses on loans and leases. + References No definition available. + Details
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- Definition Reflects unused commitments that have been issued to businesses to acquire real property, develop land for sale or construction thereon, to construct a facility and to provide financing on existing land or a building, which, pursuant to terms of the underlying debt instrument, are secured at a minimum but possibly exclusively by that real property. + References No definition available. + Details
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- Definition Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481990/310-10-45-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481962/310-10-50-4 + Details
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