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Securities - Additional Information (Details) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2021 USD ($) Investment | Jun. 30, 2020 USD ($) | Dec. 31, 2020 USD ($) Investment
Schedule of Investments [Line Items] |  |  |  |  |
Federal Home Loan Bank stock, at cost | $ | $ 686 | [1] |  | $ 714 | [2]
Net losses on equity securities | $ | $ 0 |  | $ 1 |  |
Collateralized Mortgage Obligations |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  |  |  | 4 |
Capital Trust Notes |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more | 5 |  |  | 5 |
Asset-backed Securities |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more | 4 |  |  | 7 |
Corporate Bonds |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more | 5 |  |  | 3 |
Municipal Bonds |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more | 1 |  |  | 1 |
[1] | Carrying value and estimated fair value are at cost.
[2] | Carrying value and estimated fair value are at cost.

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- Definition Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809 + Details
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