Investments in Fixed Maturity Securities (AFS Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	$ 36,708	$ 37,352
Expected credit losses on securities for which credit losses were not previously recorded	2,053	5,013
Expected credit losses on securities for which credit losses were previously recorded	(37,133)	(5,648)
Reduction due to disposals	(982)	(9)
Allowance for expected credit losses at September 30, 2020	646	36,708
Foreign Government
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	29,603	32,633
Expected credit losses on securities for which credit losses were not previously recorded	347	0
Expected credit losses on securities for which credit losses were previously recorded	(29,355)	(3,030)
Reduction due to disposals	(379)	0
Allowance for expected credit losses at September 30, 2020	216	29,603
Corporate
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	5,026	4,701
Expected credit losses on securities for which credit losses were not previously recorded	0	982
Expected credit losses on securities for which credit losses were previously recorded	(5,026)	(650)
Reduction due to disposals	0	(7)
Allowance for expected credit losses at September 30, 2020	0	5,026
Mortgage- Backed
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	158	18
Expected credit losses on securities for which credit losses were not previously recorded	1,706	1,766
Expected credit losses on securities for which credit losses were previously recorded	(831)	(1,624)
Reduction due to disposals	(603)	(2)
Allowance for expected credit losses at September 30, 2020	430	158
Asset-backed
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	1,164	0
Expected credit losses on securities for which credit losses were not previously recorded	0	1,444
Expected credit losses on securities for which credit losses were previously recorded	(1,164)	(280)
Reduction due to disposals	0	0
Allowance for expected credit losses at September 30, 2020	0	1,164
State and municipal
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	757	0
Expected credit losses on securities for which credit losses were not previously recorded	0	821
Expected credit losses on securities for which credit losses were previously recorded	(757)	(64)
Reduction due to disposals	0	0
Allowance for expected credit losses at September 30, 2020	$ 0	$ 757