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Investment Securities (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2020 USD ($) Investments_In_Single_Issuer | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Investment [Line Items] |  |  |
Percentage decrease requiring a review for impairment | 20.00% |  |
Fair value of securities on other-than-temporary impairment watch list | $ 31,000,000.0 | $ 51,600,000 |
Portfolio securities aggregate fair value loss position | 948,200,000 | 1,700,000,000 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | 6,400,000 |  |
Available for sale securities in loss position at period end, change in unrealized loss | (6,500,000) |  |
Securities pledged as collateral | 4,800,000,000 | 4,300,000,000 |
Securities pledged and may be sold or re-pledged | $ 214,200,000 |  |
Number of investments in a single issuer that exceed 10% of stockholder's equity | Investments_In_Single_Issuer | 0 |  |
No investment in a single issuer exceeds this percentage of stockholder's equity | 10.00% |  |
Visa Class B Shares [Member] |  |  |
Investment [Line Items] |  |  |
Equity Securities without Readily Determinable Fair Value, Amount | $ 0 |  |
US Treasury and Government [Member] |  |  |
Investment [Line Items] |  |  |
U.S. Treasury inflation-protected securities held | 434,600,000 |  |
Available-for-sale Securities [Member] |  |  |
Investment [Line Items] |  |  |
Net gains realized on sales of AFS debt securities | 21,096,000 | $ 2,354,000 | $ 448,000
Private Equity Funds [Member] |  |  |
Investment [Line Items] |  |  |
Fair value adjustments, net | $ (10,100,000) |  |

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