Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	$ 4,153	$ 5,247
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	4,166	4,986
Total gains (losses) (realized/unrealized):
Included in earnings	13	(261)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	13	(261)
Equity Securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Equity Securities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	13	(261)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	13	(261)
Equity Securities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	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
Short-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	10,000	0
Purchases	2,349	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	12,349	0
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Short-term investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Short-term investments | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Short-term investments | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	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
Cash equivalents
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	0	0
Purchases	100	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	100	0
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Cash equivalents | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Cash equivalents | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Cash equivalents | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Cash equivalents | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	53,980	8,059
Purchases	2,653	7,796
Sales	0	0
Issuances	0	0
Settlements	(2,133)	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	63,072	12,242
Total gains (losses) (realized/unrealized):
Included in earnings	8,572	(3,613)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	6,439	(3,613)
Other assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	8,572	(3,613)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	6,439	(3,613)
Other assets | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Other assets | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Other assets | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Reinsurance recoverables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	409,013	302,814
Purchases	4,262	4,323
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	271,390	565,090
Total gains (losses) (realized/unrealized):
Included in earnings	(141,885)	257,953
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(135,675)	260,722
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(141,885)	257,953
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(135,675)	260,722
Reinsurance recoverables | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Reinsurance recoverables | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	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
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(17,314,004)	(11,822,998)
Purchases	0	0
Sales	0	0
Issuances	(291,149)	(282,184)
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(10,511,815)	(25,302,654)
Total gains (losses) (realized/unrealized):
Included in earnings	7,093,338	(13,197,472)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	6,900,120	(13,329,640)
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	7,093,338	(13,197,472)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	6,900,120	(13,329,640)
Future policy benefits | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Future policy benefits | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	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
Policyholders' account balances
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(580,184)	(196,892)
Purchases	0	0
Sales	0	0
Issuances	(138,525)	(22,457)
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(986,479)	(158,920)
Total gains (losses) (realized/unrealized):
Included in earnings	(267,770)	60,429
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(252,703)	53,957
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(267,770)	60,429
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(252,703)	53,957
Policyholders' account balances | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Policyholders' account balances | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	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
Available-for-sale | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(44)	(110)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(37)	0
Available-for-sale | Fixed maturities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Available-for-sale | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	(987)	(14,924)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,100)	(16,067)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	(7)	(21)
Available-for-sale | Fixed maturities | U.S. government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	15,000	10,547
Purchases	0	911
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	15,000	11,458
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	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	148,687	104,267
Purchases	10,634	11,277
Sales	0	(1,155)
Issuances	0	0
Settlements	(7,627)	(2,365)
Other	0	0
Transfers into Level 3	15,147	14,349
Transfers out of Level 3	0	0
Fair Value, end of period	165,910	111,606
Total gains (losses) (realized/unrealized):
Included in earnings	(931)	(14,767)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,031)	(15,781)
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	18,542	18,825
Purchases	0	6,145
Sales	0	0
Issuances	0	0
Settlements	(1,479)	(455)
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	16,956	24,227
Total gains (losses) (realized/unrealized):
Included in earnings	(107)	(288)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(106)	(286)
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	5,045	4,464
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	5,127	3,593
Total gains (losses) (realized/unrealized):
Included in earnings	82	(871)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	87	(866)
Trading | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Trading | Fixed maturities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	88	(866)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	87	(866)
Trading | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	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	$ (6)	$ (5)