Investments in Fixed Maturity Securities (AFS Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	$ 45,493	$ 0
Cumulative effect adjustment resulting from changes in accounting principles	1,696	1,696
Expected credit losses on securities for which credit losses were not previously recorded	261	19,552
Expected credit losses on securities for which credit losses were previously recorded	(261)	(3,472)
Reduction due to disposals	(43,797)	(50,029)
Allowance for expected credit losses at September 30, 2020	1,696	1,696
Cumulative effect adjustment resulting from changes in accounting principles
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020		35,645
Cumulative effect adjustment resulting from changes in accounting principles		35,645
Foreign government
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	44,769	0
Cumulative effect adjustment resulting from changes in accounting principles	1,090	1,090
Expected credit losses on securities for which credit losses were not previously recorded	0	12,494
Expected credit losses on securities for which credit losses were previously recorded	(252)	295
Reduction due to disposals	(43,427)	(47,344)
Allowance for expected credit losses at September 30, 2020	1,090	1,090
Foreign government \| Cumulative effect adjustment resulting from changes in accounting principles
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020		35,645
Cumulative effect adjustment resulting from changes in accounting principles		35,645
Corporate
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	724	0
Cumulative effect adjustment resulting from changes in accounting principles	724	0
Expected credit losses on securities for which credit losses were not previously recorded	261	7,058
Expected credit losses on securities for which credit losses were previously recorded	(9)	(3,767)
Reduction due to disposals	(370)	(2,685)
Allowance for expected credit losses at September 30, 2020	$ 606	606
Corporate \| Cumulative effect adjustment resulting from changes in accounting principles
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020		0
Cumulative effect adjustment resulting from changes in accounting principles		$ 0

Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922900-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922900-210455

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

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Amount of expense for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), for which no credit loss was previously recorded.

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Amount of expense (reversal of expense) for allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), not intended to be sold and not more likely than not will be required to sell before recovery of amortized cost basis, with previously recorded allowance.

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Amount of decrease in allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) from sale.

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