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Fair Value of Assets and Liabilities - Changes in Fair Value of Assets and Liabilities which Fair Value Option Included in Current Period Earnings (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Mortgage banking noninterest income | Loans held for sale |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Changes in fair value included in net income | $ 0 | $ 0 | $ 2 | $ 1

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