Investments in Fixed Maturity Securities (AFS Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	$ 20,009	$ 67,356	$ 1,782	$ 0
Cumulative effect adjustment resulting from changes in accounting principles	18,911	45,493	18,911	45,493
Expected credit losses on securities for which credit losses were not previously recorded	0	361	19,006	19,291
Expected credit losses on securities for which credit losses were previously recorded	(604)	(19,580)	(1,378)	(3,211)
Reduction due to disposals	(494)	(2,644)	(499)	(6,232)
Allowance for expected credit losses, end of period	18,911	45,493	18,911	45,493
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	19,993	60,920	1,264	0
Cumulative effect adjustment resulting from changes in accounting principles	18,899	44,769	18,899	44,769
Expected credit losses on securities for which credit losses were not previously recorded	0	0	18,990	12,494
Expected credit losses on securities for which credit losses were previously recorded	(600)	(15,822)	(861)	547
Reduction due to disposals	(494)	(329)	(494)	(3,917)
Allowance for expected credit losses, end of period	18,899	44,769	18,899	44,769
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	16	6,436	518	0
Cumulative effect adjustment resulting from changes in accounting principles	12	724	12	724
Expected credit losses on securities for which credit losses were not previously recorded	0	361	16	6,797
Expected credit losses on securities for which credit losses were previously recorded	(4)	(3,758)	(517)	(3,758)
Reduction due to disposals	0	(2,315)	(5)	(2,315)
Allowance for expected credit losses, end of period	$ 12	$ 724	12	724
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