Investments in Fixed Maturity Securities (AFS Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	$ 18,911	$ 45,493	$ 1,782	$ 0
Cumulative effect adjustment resulting from changes in accounting principles	16,887	1,696	16,887	1,696
Expected credit losses on securities for which credit losses were not previously recorded	82	261	19,088	19,552
Expected credit losses on securities for which credit losses were previously recorded	(2,106)	(261)	(3,484)	(3,472)
Reduction due to disposals	0	(43,797)	(499)	(50,029)
Allowance for expected credit losses, end of period	16,887	1,696	16,887	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, beginning of period			0	35,645
Cumulative effect adjustment resulting from changes in accounting principles
Foreign government
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	18,899	44,769	1,264	0
Cumulative effect adjustment resulting from changes in accounting principles	16,875	1,090	16,875	1,090
Expected credit losses on securities for which credit losses were not previously recorded	82	0	19,072	12,494
Expected credit losses on securities for which credit losses were previously recorded	(2,106)	(252)	(2,967)	295
Reduction due to disposals	0	(43,427)	(494)	(47,344)
Allowance for expected credit losses, end of period	16,875	1,090	16,875	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, beginning of period			0	35,645
Cumulative effect adjustment resulting from changes in accounting principles
Corporate
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	12	724	518	0
Cumulative effect adjustment resulting from changes in accounting principles	12	606	12	606
Expected credit losses on securities for which credit losses were not previously recorded	0	261	16	7,058
Expected credit losses on securities for which credit losses were previously recorded	0	(9)	(517)	(3,767)
Reduction due to disposals	0	(370)	(5)	(2,685)
Allowance for expected credit losses, end of period	$ 12	$ 606	12	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, beginning of period			$ 0	$ 0
Cumulative effect adjustment resulting from changes in accounting principles