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Investment Securities - Narrative (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | ---
Aug. 05, 2025 | Sep. 30, 2025 | Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2022 | Sep. 30, 2021 | Jun. 30, 2025 | Jun. 30, 2024 | Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |
Debt securities, available-for-sale, transfer to held-to-maturity |  |  |  |  | $ 1,990,000,000 | $ 500,800,000 |  |  |
Debt securities, held-to-maturity transfer, unrealized loss |  |  |  |  |  |  | $ 99,400,000 |  |
Available-for-sale, transfer to held-to-maturity, gain (loss) |  |  |  |  |  |  | 0 |  |
Held to maturity mortgage backed securities |  |  | $ 3,594,745,000 |  |  |  | 3,594,745,000 |  | $ 3,639,850,000
Available for sale mortgage backed securities |  |  | 2,764,636,000 |  |  |  | 2,764,636,000 |  | 2,852,774,000
Held-to-maturity, interest receivable |  |  | 20,200,000 |  |  |  | 20,200,000 |  |
Available-for-sale, interest receivable |  |  | 22,200,000 |  |  |  | 22,200,000 |  |
Available-for-sale securities |  |  | 2,405,320,000 |  |  |  | 2,405,320,000 |  | 2,529,426,000
Securities valued at less than historical cost, amount |  |  | $ 2,308,482,000 |  |  |  | $ 2,308,482,000 |  | 2,467,223,000
Securities valued at less than historical cost (as percent) |  |  | 96.00% |  |  |  | 96.00% |  |
Provision for credit losses, AFS securities |  |  | $ 0 | $ 0 |  |  | $ 0 | $ 0 |
Securities pledged as collateral |  |  | 2,610,000,000 |  |  |  | 2,610,000,000 |  | 2,360,000,000
Realized gains |  |  | 0 | 0 |  |  | 0 | 0 |
Realized losses |  |  | 0 | $ 0 |  |  | $ 0 | $ 0 |
Income tax benefit related to security gains (losses) (as percent) |  |  |  |  |  |  | 26.135% | 26.135% |
Forecast |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |
Pre-tax loss |  | $ 604,000,000 |  |  |  |  |  |  |
Estimated tax rate |  | 24.30% |  |  |  |  |  |  |
Subsequent Event |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |
Debt securities, reclassified | $ 3,600,000,000 |  |  |  |  |  |  |  |
Proceeds from sale of available-for-sale securities | $ 3,200,000,000 |  |  |  |  |  |  |  |
Commercial Mortgage Backed Securities |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |
Held to maturity mortgage backed securities |  |  | 132,500,000 |  |  |  | $ 132,500,000 |  | 136,000,000.0
Available for sale mortgage backed securities |  |  | 504,200,000 |  |  |  | 504,200,000 |  | 517,200,000
Residential Mortgage Backed Securities |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |
Held to maturity mortgage backed securities |  |  | 891,800,000 |  |  |  | 891,800,000 |  | 934,100,000
Available for sale mortgage backed securities |  |  | $ 845,800,000 |  |  |  | $ 845,800,000 |  | $ 875,500,000

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