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Derivatives and Hedging Activities - Impact of Fair Value Hedge Accounting on the Carrying Value of the Hedged Items (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Jun. 30, 2024 | Jun. 30, 2024 | Sep. 30, 2023
Derivatives, Fair Value [Line Items] |  |  |
Carrying value of hedged items | $ 7,385,202,000 | $ 7,385,202,000 | $ 1,816,870,000
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items | (40,379,000) | (40,379,000) | (48,865,000)
Mortgage loan fair value hedges |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Portfolio layer method, amortized cost | 7,350,681,000 | 7,350,681,000 | 1,780,503,000
Portfolio layer method, cumulative adjustment, increase (decrease) | (37,908,000) | (37,908,000) | (45,622,000)
Amortized cost, designated in portfolio hedging relationship | 2,670,000,000 | 2,670,000,000 | 670,000,000
Hedged asset, discontinued | 300,000,000 | 300,000,000 |
Hedged asset, discontinued, basis adjustment | 1,232,211 | 1,232,211 |
Commercial loan fair value hedges |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Carrying value of hedged items | 34,521,000 | 34,521,000 | 36,367,000
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items | $ (2,471,000) | $ (2,471,000) | $ (3,243,000)

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