Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets:
Policy loans	$ 1,496,241	$ 1,472,677
Cash and cash equivalents	2,357,758	2,139,792
Accrued investment income	361,054	333,838
Reinsurance recoverables	41,124,532	38,709,651
Receivables from parent and affiliates	514,254	332,583
Liabilities
Cash collateral for loaned securities	3,698	218,310
Fair Value
Assets:
Commercial mortgage and other loans	6,039,321	5,918,386
Policy loans	1,496,241	1,472,677
Short-term investments	120,007	66,500
Cash and cash equivalents	448,086	495,667
Accrued investment income	361,054	333,838
Reinsurance recoverables	21,774	22,155
Receivables from parent and affiliates	244,305	184,599
Other assets	1,787,957	1,570,629
Total assets	10,518,745	10,064,451
Liabilities
Policyholders’ account balances - investment contracts	7,716,851	6,352,532
Cash collateral for loaned securities	3,698	218,310
Short-term debt to affiliates	179,115	176,110
Payables to parent and affiliates	73,514	16,573
Other liabilities	2,384,888	2,154,284
Total liabilities	10,358,066	8,917,809
Carrying Amount
Assets:
Commercial mortgage and other loans	6,279,862	6,122,721
Policy loans	1,496,241	1,472,677
Short-term investments	120,007	66,500
Cash and cash equivalents	448,086	495,667
Accrued investment income	361,054	333,838
Reinsurance recoverables	23,385	23,537
Receivables from parent and affiliates	244,305	184,599
Other assets	1,787,957	1,570,629
Total assets	10,760,897	10,270,168
Liabilities
Policyholders’ account balances - investment contracts	7,733,251	6,368,061
Cash collateral for loaned securities	3,698	218,310
Short-term debt to affiliates	179,115	180,411
Payables to parent and affiliates	73,514	16,573
Other liabilities	2,384,888	2,154,283
Total liabilities	10,374,466	8,937,638
Level 1 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	120,007	66,500
Cash and cash equivalents	448,086	470,668
Accrued investment income	0	0
Reinsurance recoverables	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	568,093	537,168
Liabilities
Policyholders’ account balances - investment contracts	0	0
Cash collateral for loaned securities	0	0
Short-term debt to affiliates	0	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	0	24,999
Accrued investment income	361,054	333,838
Reinsurance recoverables	0	0
Receivables from parent and affiliates	244,305	184,599
Other assets	50,157	80,646
Total assets	655,516	624,082
Liabilities
Policyholders’ account balances - investment contracts	912,874	955,647
Cash collateral for loaned securities	3,698	218,310
Short-term debt to affiliates	179,115	176,110
Payables to parent and affiliates	73,514	16,573
Other liabilities	2,352,465	2,121,861
Total liabilities	3,521,666	3,488,501
Level 3 | Fair Value
Assets:
Commercial mortgage and other loans	6,039,321	5,918,386
Policy loans	1,496,241	1,472,677
Short-term investments	0	0
Cash and cash equivalents	0	0
Accrued investment income	0	0
Reinsurance recoverables	21,774	22,155
Receivables from parent and affiliates	0	0
Other assets	1,737,800	1,489,983
Total assets	9,295,136	8,903,201
Liabilities
Policyholders’ account balances - investment contracts	6,803,977	5,396,885
Cash collateral for loaned securities	0	0
Short-term debt to affiliates	0	0
Payables to parent and affiliates	0	0
Other liabilities	32,423	32,423
Total liabilities	$ 6,836,400	$ 5,429,308