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Investments (Fixed Maturity Securities Pledged And Received As Collateral) (Details) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017
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Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | $ 22,249,964 | $ 21,966,803
Available-for-sale Securities | 22,503,507 | 23,210,968
Collateral Fixed Maturity Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 63,640 | 72,542
Available-for-sale Securities | 66,118 | 75,622
Collateral Received Fixed Maturity Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities | 626,081 | 590,417
Reported Value Measurement [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Assets Held-in-trust | 16,061,218 | 15,584,296
Estimate of Fair Value Measurement [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Assets Held-in-trust | $ 16,571,173 | $ 16,715,281

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- Definition The total amount of cash and securities held by third party trustees pursuant to terms of debt instruments or other agreements as of the date of each statement of financial position presented, which can be used by the trustee only to pay the noncurrent portion of specified obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(b)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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