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Loans - Asset Quality Indicators (Details) | Mar. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | [1] | Mar. 31, 2019 USD ($)
--- | --- | --- | --- | ---
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans, net of unearned income | $ 33,378,303,000 | [1] | $ 31,061,111,000 | $ 27,990,048,000
Commercial | PD Grade 1 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Lowest expected default probability | 1 |  |  |
Commercial | Loss |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 16 |  |  |
Commercial | Special Mention |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 13 |  |  |
Commercial | Substandard |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 14 |  |  |
Commercial | Doubtful |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 15 |  |  |
Commercial | Minimum | Pass |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 1 |  |  |
Commercial | Minimum | Special Mention |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 13 |  |  |
Commercial | Minimum | Loan Reassessed |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans, net of unearned income | $ 1,000,000 |  |  |
Commercial | Minimum | PD Grade 13 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans, net of unearned income | $ 500,000 |  |  |
Commercial | Minimum | LGD Grade 1 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 1 |  |  |
Commercial | Maximum | Loss |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 16 |  |  |
Commercial | Maximum | Pass |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 12 |  |  |
Commercial | Maximum | LGD Grade 12 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial loan grades | 12 |  |  |
[1] | March 31, 2020 and December 31, 2019 include $20.8 million and $18.8 million, respectively, of held-to-maturity consumer mortgage loans secured by residential real estate in process of foreclosure.

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