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Investment Securities - Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items] |  |  |  |
Debt securities, available-for-sale, transfer to held-to-maturity | $ 500,800,000 |  |  |
Unrealized gains on securities transferred from AFS to HTM |  | $ 1,000,000 |  |
Available-for-sale, transfer to held-to-maturity, gain (loss) | $ 0 |  |  |
Amortized Cost |  | 1,530,500,000 | $ 335,946,000 |
Available-for-sale, amortized cost |  | 7,130,861,000 | 3,397,043,000 |
Held-to-maturity, interest receivable |  | 9,700,000 |  |
Available-for-sale, interest receivable |  | 23,400,000 |  |
Available-for-sale securities |  | 7,113,545,000 | 3,473,598,000 |
Securities valued at less than historical cost, amount |  | $ 5,065,704,000 |  |
Securities continuous unrealized loss position fair value (as percent) |  | 71.20% |  |
Decrease in available-for-sale provision for credit losses |  | $ (312,000) | (61,000) | $ 0
Securities pledged as collateral |  | 3,900,000,000 | 2,000,000,000 |
Realized gains |  | 15,900,000 | 54,800,000 | 13,300,000
Realized losses |  | $ 422,000 | $ 15,000 | $ 4,000
Income tax benefit related to security gains (losses) (as percent) |  | 26.135% | 26.135% | 26.135%
Bonds |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |
Investments sold, amount |  | $ 342,600,000 | $ 1,700,000,000 |
Commercial Mortgage Backed Securities |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |
Amortized Cost |  | 4,900,000 | 7,700,000 |
Available-for-sale, amortized cost |  | 1,530,000,000 | 406,100,000 |
Residential Mortgage Backed Securities |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |
Amortized Cost |  | 65,500,000 | 14,700,000 |
Available-for-sale, amortized cost |  | $ 2,920,000,000 | $ 988,800,000 |

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