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Investments (Narrative) (Details) shares in Thousands |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Nov. 01, 2020 USD ($) | Sep. 30, 2021 USD ($) investment investments shares | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) investment investments shares | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Schedule of Investments [Line Items] |  |  |  |  |  |
Unrealized gain at the date of transfer | $ 5,900,000 |  |  |  |  |
Other Comprehensive Income Loss Unrealized Losses On Securities Available For Sale Transferred To Held To Maturity Arising During Period Net Of Tax | 4,500,000 | $ (331,000) | $ 0 | $ (1,301,000) | $ 0 |
Stock issued by Federal Home Loan Bank |  | 40,500,000 |  | 40,500,000 |  | $ 45,400,000
Non-marketable equity securities |  | 9,600,000 |  | 9,600,000 |  | 11,600,000
Available for sale securities, realized gain (loss) |  | $ 8,082,000 | $ 21,425,000 | $ 33,119,000 | $ 54,972,000 |
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, number of positions | investment |  | 36 |  | 36 |  |
Unrealized losses related to marketability of securities or issuer's ability to honor redemption obligations |  | $ 0 |  | $ 0 |  |
Investment value deemed to be OTTI |  |  |  | 0 |  |
Investment securities, aggregate carrying value, pledged as collateral |  | 5,500,000,000 |  | 5,500,000,000 |  | $ 4,600,000,000
Debt Securities, Accrued Interest, WriteOff |  | 0 |  | 0 |  |
Held-to-maturity securities |  | 0 |  | 0 |  |
Past due securities |  | $ 0 |  | $ 0 |  |
Residential mortgage-backed securities |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Investment securities available for sale transferred to held to maturity amortized cost | 1,460,000,000 |  |  |  |  |
Investment securities available for sale transferred to held to maturity fair value | $ 1,470,000,000 |  |  |  |  |
Weighted average contractual maturity term | 18 years |  |  |  |  |
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, number of positions | investments |  | 34 |  | 34 |  |
Corporate Bonds |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, number of positions | investments |  | 2 |  | 2 |  |
Visa Class B Common Stock |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Investment owned (in shares) | shares |  | 354 |  | 354 |  |
Investment owned, fair value |  | $ 0 |  | $ 0 |  |

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