Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Assets:
Policy loans	$ 1,432,850	$ 505,367
Cash and cash equivalents	1,780,991	2,397,627
Accrued investment income	283,585	219,635
Reinsurance recoverables	37,667,480	37,096,562	[1]
Receivables from parent and affiliates	267,218	224,921
Liabilities [Abstract]
Cash collateral for loaned securities	162,122	86,750
Fair Value
Assets:
Commercial mortgage and other loans	5,054,111	4,602,177
Policy loans	1,432,850	505,367
Short-term investments	68,756	26,331
Cash and cash equivalents	688,597	965,445
Accrued investment income	283,585	219,635
Reinsurance recoverables	23,550	25,127
Receivables from parent and affiliates	121,557	76,846
Other assets	1,263,387	824,882
Total assets	8,936,393	7,245,810
Liabilities [Abstract]
Policyholders’ account balances - investment contracts	5,222,559	4,333,271
Cash collateral for loaned securities	162,122	86,750
Short-term debt to affiliates	294,570	120,325
Long-term debt to affiliates	0	173,905
Payables to parent and affiliates	15,532	41,654
Other liabilities	1,705,683	1,302,865
Total liabilities	7,400,466	6,058,770
Carrying Amount
Assets:
Commercial mortgage and other loans	5,382,278	4,928,680
Policy loans	1,432,850	505,367
Short-term investments	68,756	26,331
Cash and cash equivalents	688,597	965,445
Accrued investment income	283,585	219,635
Reinsurance recoverables	25,682	27,183
Receivables from parent and affiliates	121,557	76,846
Other assets	1,263,387	824,882
Total assets	9,266,692	7,574,369
Liabilities [Abstract]
Policyholders’ account balances - investment contracts	5,243,834	4,351,945
Cash collateral for loaned securities	162,122	86,750
Short-term debt to affiliates	307,123	126,250
Long-term debt to affiliates	0	185,563
Payables to parent and affiliates	15,532	41,654
Other liabilities	1,705,683	1,302,866
Total liabilities	7,434,294	6,095,028
Level 1 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	68,756	26,331
Cash and cash equivalents	688,597	675,445
Accrued investment income	0	0
Reinsurance recoverables	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	757,353	701,776
Liabilities [Abstract]
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	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	290,000
Accrued investment income	283,585	219,635
Reinsurance recoverables	0	0
Receivables from parent and affiliates	121,557	76,846
Other assets	54,945	94,200
Total assets	460,087	680,681
Liabilities [Abstract]
Policyholders’ account balances - investment contracts	1,074,738	1,192,271
Cash collateral for loaned securities	162,122	86,750
Short-term debt to affiliates	294,570	120,325
Long-term debt to affiliates	0	173,905
Payables to parent and affiliates	15,532	41,654
Other liabilities	1,673,260	1,269,615
Total liabilities	3,220,222	2,884,520
Level 3 | Fair Value
Assets:
Commercial mortgage and other loans	5,054,111	4,602,177
Policy loans	1,432,850	505,367
Short-term investments	0	0
Cash and cash equivalents	0	0
Accrued investment income	0	0
Reinsurance recoverables	23,550	25,127
Receivables from parent and affiliates	0	0
Other assets	1,208,442	730,682
Total assets	7,718,953	5,863,353
Liabilities [Abstract]
Policyholders’ account balances - investment contracts	4,147,821	3,141,000
Cash collateral for loaned securities	0	0
Short-term debt to affiliates	0	0
Long-term debt to affiliates	0	0
Payables to parent and affiliates	0	0
Other liabilities	32,423	33,250
Total liabilities	$ 4,180,244	$ 3,174,250

[1] Prior period amounts adjusted for the implementation of Accounting Standard Update ("ASU") 2018-12: Targeted Improvements to the Accounting for Long-Duration Contracts.