Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	$ 9,150	$ 17,105	$ 9,898	$ 15,997
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	10,912	17,371	10,912	17,371
Total gains (losses) (realized/unrealized):
Included in earnings	1,762	266	1,014	1,374
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,762	266	1,014	1,374
Equity securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Equity securities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	1,762	266	1,014	1,374
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,762	266	1,014	1,374
Equity securities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Equity securities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	0	4	4	4
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	0	4	0	4
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	(4)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	(4)	0
Other invested assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	(4)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	(4)	0
Other invested assets | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Other invested assets | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Other invested assets | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Short-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	0	94	0	0
Purchases	0	606	0	1,069
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	(244)	0	(613)
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	0	456	0	456
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Short-term investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Short-term investments | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Short-term investments | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Short-term investments | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Reinsurance recoverables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	19,028,138	8,485,905	8,539,671	5,600,008
Purchases	278,413	259,782	815,920	739,173
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	16,675,343	11,313,614	16,675,343	11,313,614
Total gains (losses) (realized/unrealized):
Included in earnings	(2,631,208)	2,567,927	7,319,752	4,974,433
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(2,473,607)	2,653,797	7,534,062	5,127,527
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(2,631,208)	2,567,927	7,319,752	4,974,433
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(2,473,607)	2,653,797	7,534,062	5,127,527
Reinsurance recoverables | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Reinsurance recoverables | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Reinsurance recoverables | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Receivables from parents and affiliates
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	0	6,295	3,135	9,261
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	(1,578)	(3,158)	(4,737)
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	0	4,682	0	4,682
Total gains (losses) (realized/unrealized):
Included in earnings	0	(35)	23	158
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Receivables from parents and affiliates | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Receivables from parents and affiliates | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Receivables from parents and affiliates | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Receivables from parents and affiliates | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	(35)	23	158
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(19,014,066)	(8,476,541)	(8,529,566)	(5,588,840)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(276,460)	(257,739)	(810,047)	(733,241)
Settlements	0	0	0	0
Other	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	(16,661,255)	(11,302,531)	(16,661,255)	(11,302,531)
Total gains (losses) (realized/unrealized):
Included in earnings	2,629,271	(2,568,251)	(7,321,642)	(4,980,450)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,475,638	(2,655,925)	(7,535,951)	(5,133,545)
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	2,629,271	(2,568,251)	(7,321,642)	(4,980,450)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,475,638	(2,655,925)	(7,535,951)	(5,133,545)
Future policy benefits | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Future policy benefits | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Future policy benefits | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Policyholders' account balances
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(1,045,483)	(786,969)	(962,351)	(13,015)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(29,368)	(115,012)	(152,460)	(163,425)
Settlements	0	0	0	0
Other	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	(1,076,904)	(875,975)	(1,076,904)	(875,975)
Total gains (losses) (realized/unrealized):
Included in earnings	(2,053)	26,006	37,907	(699,535)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	11,350	35,117	53,610	(689,872)
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(2,053)	26,006	37,907	(699,535)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	11,350	35,117	53,610	(689,872)
Policyholders' account balances | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Policyholders' account balances | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Policyholders' account balances | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Available-for-sale | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(1,084)	(1,549)	(5,224)	(4,616)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,086)	(1,731)	(4,780)	(4,893)
Available-for-sale | Fixed maturities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Available-for-sale | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	5,003	1,406	7,034	2,248
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	5,004		7,415
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	22	144	122	507
Available-for-sale | Fixed maturities | US government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	44,792	34,392	38,671	29,816
Purchases	3,667	1,847	9,788	6,423
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	48,459	36,239	48,459	36,239
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Available-for-sale | Fixed maturities | Foreign government bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	161	165	163	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	159
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	164	164	164	164
Total gains (losses) (realized/unrealized):
Included in earnings	3	(1)	1	5
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2	0	0	0
Available-for-sale | Fixed maturities | Corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	156,972	54,014	50,083	56,588
Purchases	2,436	796	11,100	2,918
Sales	0	(28)	(3,680)	(81)
Issuances	0	0	0	0
Settlements	(538)	(1,158)	(6,873)	(10,839)
Other	(1,914)	0	(1,914)	0
Transfers into Level 3	0	5,247	109,772	13,463
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	160,897	58,857	160,897	58,857
Total gains (losses) (realized/unrealized):
Included in earnings	3,941	(14)	2,409	(3,192)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	3,920	(1,731)	3,113	(4,893)
Available-for-sale | Fixed maturities | Structured securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	1,507	4,297	2,001	6,556
Purchases	1,299	0	7,444	0
Sales	0	(101)	0	(103)
Issuances	0	0	0	0
Settlements	(262)	(178)	(790)	(4,334)
Other	0	0	0	0
Transfers into Level 3	0	0	0	77,660
Transfers out of Level 3	0	0	(5,636)	(77,071)
Fair Value, end of period	2,541	4,034	2,541	4,034
Total gains (losses) (realized/unrealized):
Included in earnings	(3)	16	(478)	1,326
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(4)	0	(478)	0
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	644	605	668	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	751
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	698	593	698	593
Total gains (losses) (realized/unrealized):
Included in earnings	54	(12)	30	(158)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	55	(12)	30	(158)
Trading | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Trading | Fixed maturities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	54	(12)	30	(158)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	55	(12)	30	(158)
Trading | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0		0
Trading | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	$ 0	$ 0	$ 0	$ 0