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Investments - Corporate Debt Securities by Industry Group (Details) | Jun. 30, 2019 | Dec. 31, 2018
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Debt Securities By Industry [Line Items] |  |
Corporate debt securities as component of total (percent) | 100.00% | 100.00%
Financial |  |
Debt Securities By Industry [Line Items] |  |
Corporate debt securities as component of total (percent) | 38.00% | 38.00%
Consumer |  |
Debt Securities By Industry [Line Items] |  |
Corporate debt securities as component of total (percent) | 27.00% | 27.00%
Communications |  |
Debt Securities By Industry [Line Items] |  |
Corporate debt securities as component of total (percent) | 10.00% | 12.00%
Utilities |  |
Debt Securities By Industry [Line Items] |  |
Corporate debt securities as component of total (percent) | 9.00% | 7.00%
Industrial |  |
Debt Securities By Industry [Line Items] |  |
Corporate debt securities as component of total (percent) | 8.00% | 7.00%
Technology |  |
Debt Securities By Industry [Line Items] |  |
Corporate debt securities as component of total (percent) | 6.00% | 6.00%
Energy |  |
Debt Securities By Industry [Line Items] |  |
Corporate debt securities as component of total (percent) | 1.00% | 2.00%
Other |  |
Debt Securities By Industry [Line Items] |  |
Corporate debt securities as component of total (percent) | 1.00% | 1.00%

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