Investments (Fixed Maturity Securities Pledged And Received As Collateral) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
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

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.

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

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+ References

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