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Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Additional Information (Details) - USD ($) $ in Millions | 6 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2021 | Mar. 31, 2021 | Dec. 31, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Allowance for credit loss | $ 12,346 |  | $ 15,564 |  |  |
Allowance for credit losses |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Increase (Decrease) in Allowance for Credit Loss | (3,200) |  |  |  |  |
Allowance for credit loss | $ 12,346 | $ 14,017 | $ 15,564 | $ 16,832 | $ 14,073 | $ 7,208

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