Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Assets:
Policy loans	$ 1,472,677	$ 505,367
Short-term investments	380,366
Cash and cash equivalents	2,139,792	2,397,627
Accrued investment income	333,838	219,635
Reinsurance recoverables	38,709,651	37,096,562
Receivables from parent and affiliates	332,583	224,921
Liabilities:
Cash collateral for loaned securities	218,310	86,750
Fair Value
Assets:
Commercial mortgage and other loans	5,918,386	4,602,177
Policy loans	1,472,677	505,367
Short-term investments	66,500	26,331
Cash and cash equivalents	495,667	965,445
Accrued investment income	333,838	219,635
Reinsurance recoverables	22,155	25,127
Receivables from parent and affiliates	184,599	76,846
Other assets	1,570,629	824,882
Total assets	10,064,451	7,245,810
Liabilities:
Policyholders’ account balances - investment contracts	6,352,532	4,333,271
Cash collateral for loaned securities	218,310	86,750
Short-term debt to affiliates	176,110	120,325
Long-term debt to affiliates		173,905
Payables to parent and affiliates	16,573	41,654
Other liabilities	2,154,284	1,302,865
Total liabilities	8,917,809	6,058,770
Carrying Amount
Assets:
Commercial mortgage and other loans	6,122,721	4,928,680
Policy loans	1,472,677	505,367
Short-term investments	66,500	26,331
Cash and cash equivalents	495,667	965,445
Accrued investment income	333,838	219,635
Reinsurance recoverables	23,537	27,183
Receivables from parent and affiliates	184,599	76,846
Other assets	1,570,629	824,882
Total assets	10,270,168	7,574,369
Liabilities:
Policyholders’ account balances - investment contracts	6,368,061	4,351,945
Cash collateral for loaned securities	218,310	86,750
Short-term debt to affiliates	180,411	126,250
Long-term debt to affiliates		185,563
Payables to parent and affiliates	16,573	41,654
Other liabilities	2,154,283	1,302,866
Total liabilities	8,937,638	6,095,028
Level 1 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	66,500	26,331
Cash and cash equivalents	470,668	675,445
Accrued investment income	0	0
Reinsurance recoverables	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	537,168	701,776
Liabilities:
Policyholders’ account balances - investment contracts	0	0
Cash collateral for loaned securities	0	0
Short-term debt to affiliates	0	0
Long-term debt to affiliates		0
Payables to parent and affiliates	0	0
Other liabilities	0	0
Total liabilities	0	0
Level 2 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	0	0
Cash and cash equivalents	24,999	290,000
Accrued investment income	333,838	219,635
Reinsurance recoverables	0	0
Receivables from parent and affiliates	184,599	76,846
Other assets	80,646	94,200
Total assets	624,082	680,681
Liabilities:
Policyholders’ account balances - investment contracts	955,647	1,192,271
Cash collateral for loaned securities	218,310	86,750
Short-term debt to affiliates	176,110	120,325
Long-term debt to affiliates		173,905
Payables to parent and affiliates	16,573	41,654
Other liabilities	2,121,861	1,269,615
Total liabilities	3,488,501	2,884,520
Level 3 | Fair Value
Assets:
Commercial mortgage and other loans	5,918,386	4,602,177
Policy loans	1,472,677	505,367
Short-term investments	0	0
Cash and cash equivalents	0	0
Accrued investment income	0	0
Reinsurance recoverables	22,155	25,127
Receivables from parent and affiliates	0	0
Other assets	1,489,983	730,682
Total assets	8,903,201	5,863,353
Liabilities:
Policyholders’ account balances - investment contracts	5,396,885	3,141,000
Cash collateral for loaned securities	0	0
Short-term debt to affiliates	0	0
Long-term debt to affiliates		0
Payables to parent and affiliates	0	0
Other liabilities	32,423	33,250
Total liabilities	$ 5,429,308	$ 3,174,250