Investments in Fixed Maturity Securities (AFS Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	$ 44,248	$ 33,278	$ 37,352	$ 22,238
Cumulative effect adjustment resulting from changes in accounting principles	46,364	34,595	46,364	34,595
Expected credit losses on securities for which credit losses were not previously recorded	2,482	1,044	4,973	3,123
Expected credit losses (gains) on securities for which credit losses were previously recorded	(366)	273	4,046	9,267
Reduction due to disposals			(7)	(33)
Allowance for expected credit losses, end of period	46,364	34,595	46,364	34,595
Foreign government
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	33,052	33,096	32,633	22,222
Cumulative effect adjustment resulting from changes in accounting principles	36,171	33,375	36,171	33,375
Expected credit losses on securities for which credit losses were not previously recorded	0	0	0	1,897
Expected credit losses (gains) on securities for which credit losses were previously recorded	3,119	279	3,538	9,289
Reduction due to disposals			0	(33)
Allowance for expected credit losses, end of period	36,171	33,375	36,171	33,375
Corporate
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	8,867	182	4,701	16
Cumulative effect adjustment resulting from changes in accounting principles	5,770	1,199	5,770	1,199
Expected credit losses on securities for which credit losses were not previously recorded	756	1,023	942	1,205
Expected credit losses (gains) on securities for which credit losses were previously recorded	(3,853)	(6)	134	(22)
Reduction due to disposals			(7)	0
Allowance for expected credit losses, end of period	5,770	1,199	5,770	1,199
Mortgage-backed
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	885	0	18	0
Cumulative effect adjustment resulting from changes in accounting principles	2,100	21	2,100	21
Expected credit losses on securities for which credit losses were not previously recorded	905	21	1,766	21
Expected credit losses (gains) on securities for which credit losses were previously recorded	310	0	316	0
Reduction due to disposals			0	0
Allowance for expected credit losses, end of period	2,100	$ 21	2,100	$ 21
Asset-backed
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	1,444		0
Cumulative effect adjustment resulting from changes in accounting principles	1,502		1,502
Expected credit losses on securities for which credit losses were not previously recorded	0		1,444
Expected credit losses (gains) on securities for which credit losses were previously recorded	58		58
Reduction due to disposals			0
Allowance for expected credit losses, end of period	1,502		1,502
State and municipal
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	821		821
Expected credit losses on securities for which credit losses were not previously recorded	821		821
Expected credit losses (gains) on securities for which credit losses were previously recorded	0		0
Reduction due to disposals			0
Allowance for expected credit losses, end of period	$ 821		$ 821