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Investments (Fixed Maturity Securities Pledged And Received As Collateral) (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2020 | Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items] |  |
Document Period End Date | Mar. 31, 2020 |
Collateral Fixed Maturity Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | $ 142 | $ 113
Available-for-sale Securities | 154 | 116
Collateral Received Fixed Maturity Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities | 1,172 | 727
Reported Value Measurement [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Assets Held-in-trust | 27,080 | 27,290
Estimate of Fair Value Measurement [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Assets Held-in-trust | $ 27,441 | $ 29,239

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