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Investments (Narrative) (Details) shares in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 USD ($) investment investments shares | Sep. 30, 2019 USD ($) | Sep. 30, 2020 USD ($) investment investments shares | Sep. 30, 2019 USD ($) | Dec. 31, 2019 USD ($)
Schedule of Investments [Line Items] |  |  |  |  |
Stock issued by Federal Home Loan Bank | $ 45,400,000 |  | $ 45,400,000 |  | $ 43,000,000.0
Non-marketable equity securities | 13,500,000 |  | 13,500,000 |  | 12,500,000
Available for sale securities, realized gain (loss) | $ 21,425,000 | $ 1,136,000 | $ 54,972,000 | $ 6,855,000 |
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, number of positions | investment | 38 |  | 38 |  |
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 | 4,480,000,000 |  | 4,480,000,000 |  | $ 3,930,000,000
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] |  |  |  |  |
Available-for-sale, securities in unrealized loss positions, number of positions, greater than or equal to one year | investments | 37 |  | 37 |  |
Corporate Bonds |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Available-for-sale, securities in unrealized loss positions, number of positions, greater than or equal to one year | investments | 1 |  | 1 |  |
Visa Class B Common Stock |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Investment owned (in shares) | shares | 354 |  | 354 |  |
Investment owned | $ 0 |  | $ 0 |  |

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