Fair Value of Assets and Liabilities (Balances of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022		Sep. 30, 2022
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	$ 23,798,355	$ 19,025,401
Market risk benefits assets	2,519,234	1,393,237	[1]	$ 1,306,000
Fixed maturities, trading	2,444,273	1,936,159
Equity securities	224,397	143,072
Other invested assets	1,203,591	1,088,613
Other assets	2,029,917	1,331,427	[1]
Reinsurance recoverables	36,860,011	37,096,562	[1]
Receivables from parent and affiliates	231,879	224,921
Separate account assets	111,611,386	114,051,246
TOTAL ASSETS	199,893,920	193,473,118
Market risk benefit liabilities	4,371,178	5,521,601	[1]	$ 5,945,000
Payables to parent and affiliates	3,966,688	2,126,571
Total liabilities	196,077,003	188,436,923
Fair Value, Measurements, Recurring
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	23,798,355	19,025,401
Market risk benefits assets	2,519,234	1,393,237
Fixed maturities, trading	2,444,273	1,936,159
Equity securities	224,397	143,072
Short-term investments	221,067	98,160
Cash equivalents	1,144,914	1,432,182
Other invested assets	34,591	47,111
Other assets	270,490	141,041
Reinsurance recoverables	15,544
Receivables from parent and affiliates	144,699	148,075
Subtotal excluding separate account assets	30,817,564	24,364,438
Separate account assets	106,654,589	108,789,313
TOTAL ASSETS	137,472,153	133,153,751
Market risk benefit liabilities	4,371,178	5,521,601
Policyholders’ account balances	6,005,729	3,502,096
Payables to parent and affiliates	3,935,434	2,084,917
Other liabilities	3,734	(9,267)
Total liabilities	14,316,075	11,099,347
Assets netting	(12,276,734)	(7,637,939)
Liabilities netting	(21,871,933)	(16,568,912)
Netting	(9,595,000)	(8,931,000)
Fair Value, Measurements, Recurring | Other invested assets
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets netting	(12,276,734)	(7,637,939)
Fair Value, Measurements, Recurring | Payables to parent and affiliates
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities netting	(21,870,566)	(16,568,242)
Fair Value, Measurements, Recurring | Other liabilities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities netting	(1,367)	(670)
Fair Value, Measurements, Recurring | U.S. Treasury securities and obligations of U.S. government authorities and agencies
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	293,060	281,792
Fair Value, Measurements, Recurring | Obligations of U.S. states and their political subdivisions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	731,917	628,200
Fair Value, Measurements, Recurring | Foreign government bonds
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	267,033	273,462
Fair Value, Measurements, Recurring | U.S. corporate public securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	8,836,174	6,443,944
Fair Value, Measurements, Recurring | U.S. corporate private securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	4,532,015	3,816,729
Fair Value, Measurements, Recurring | Foreign corporate public securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	1,694,468	1,378,222
Fair Value, Measurements, Recurring | Foreign corporate private securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	4,200,172	3,766,330
Fair Value, Measurements, Recurring | Asset-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	2,029,708	1,442,354
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	832,787	658,152
Fair Value, Measurements, Recurring | Residential mortgage-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	381,021	336,216
Fair Value, Measurements, Recurring | Level 1
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Market risk benefits assets	0	0
Fixed maturities, trading	0	0
Equity securities	169,378	108,076
Short-term investments	19,809	0
Cash equivalents	0	0
Other invested assets	9,208	4,223
Other assets	0	0
Reinsurance recoverables	0
Receivables from parent and affiliates	0	0
Subtotal excluding separate account assets	198,395	112,299
Separate account assets	130,896	102,243
TOTAL ASSETS	329,291	214,542
Market risk benefit liabilities	0	0
Policyholders’ account balances	0	0
Payables to parent and affiliates	0	0
Other liabilities	10,497	899
Total liabilities	10,497	899
Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury securities and obligations of U.S. government authorities and agencies
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Obligations of U.S. states and their political subdivisions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Foreign government bonds
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 1 | U.S. corporate public securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 1 | U.S. corporate private securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Foreign corporate public securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Foreign corporate private securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Asset-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Commercial mortgage-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Residential mortgage-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	22,662,905	18,412,457
Market risk benefits assets	0	0
Fixed maturities, trading	2,443,548	1,936,159
Equity securities	10,333	6,403
Short-term investments	200,674	81,215
Cash equivalents	1,144,914	1,432,182
Other invested assets	12,302,117	7,680,827
Other assets	0	0
Reinsurance recoverables	0
Receivables from parent and affiliates	144,699	148,075
Subtotal excluding separate account assets	38,909,190	29,697,318
Separate account assets	106,518,193	108,682,425
TOTAL ASSETS	145,427,383	138,379,743
Market risk benefit liabilities	0	0
Policyholders’ account balances	0	0
Payables to parent and affiliates	25,806,000	18,653,159
Other liabilities	(5,396)	(9,496)
Total liabilities	25,800,604	18,643,663
Fair Value, Measurements, Recurring | Level 2 | U.S. Treasury securities and obligations of U.S. government authorities and agencies
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	293,060	281,792
Fair Value, Measurements, Recurring | Level 2 | Obligations of U.S. states and their political subdivisions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	731,917	628,200
Fair Value, Measurements, Recurring | Level 2 | Foreign government bonds
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	266,347	272,738
Fair Value, Measurements, Recurring | Level 2 | U.S. corporate public securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	8,836,174	6,443,944
Fair Value, Measurements, Recurring | Level 2 | U.S. corporate private securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	4,065,855	3,573,269
Fair Value, Measurements, Recurring | Level 2 | Foreign corporate public securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	1,687,936	1,371,354
Fair Value, Measurements, Recurring | Level 2 | Foreign corporate private securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	3,728,278	3,509,162
Fair Value, Measurements, Recurring | Level 2 | Asset-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	1,916,281	1,421,852
Fair Value, Measurements, Recurring | Level 2 | Commercial mortgage-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	756,036	573,930
Fair Value, Measurements, Recurring | Level 2 | Residential mortgage-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	381,021	336,216
Fair Value, Measurements, Recurring | Level 3
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	1,135,450	612,944
Market risk benefits assets	2,519,234	1,393,237
Fixed maturities, trading	725	0
Equity securities	44,686	28,593
Short-term investments	584	16,945
Cash equivalents	0	0
Other invested assets	0	0
Other assets	270,490	141,041
Reinsurance recoverables	15,544
Receivables from parent and affiliates	0	0
Subtotal excluding separate account assets	3,986,713	2,192,760
Separate account assets	5,500	4,645
TOTAL ASSETS	3,992,213	2,197,405
Market risk benefit liabilities	4,371,178	5,521,601
Policyholders’ account balances	6,005,729	3,502,096
Payables to parent and affiliates	0	0
Other liabilities	0	0
Total liabilities	10,376,907	9,023,697
Fair Value, Measurements, Recurring | Level 3 | U.S. Treasury securities and obligations of U.S. government authorities and agencies
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Obligations of U.S. states and their political subdivisions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Foreign government bonds
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	686	724
Fair Value, Measurements, Recurring | Level 3 | U.S. corporate public securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Fair Value, Measurements, Recurring | Level 3 | U.S. corporate private securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	466,160	243,460
Fair Value, Measurements, Recurring | Level 3 | Foreign corporate public securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	6,532	6,868
Fair Value, Measurements, Recurring | Level 3 | Foreign corporate private securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	471,894	257,168
Fair Value, Measurements, Recurring | Level 3 | Asset-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	113,427	20,502
Fair Value, Measurements, Recurring | Level 3 | Commercial mortgage-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	76,751	84,222
Fair Value, Measurements, Recurring | Level 3 | Residential mortgage-backed securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, available-for-sale	0	0
Other invested assets
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value investment measured at NAV per share	65,000	69,000
Separate account assets
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value investment measured at NAV per share	$ 4,957,000	$ 5,262,000

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