Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	$ 9,898	$ 15,997
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	9,196	15,991
Total gains (losses) (realized/unrealized):
Included in earnings	(702)	(6)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(702)	(6)
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	(702)	(6)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(702)	(6)
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
Equity securities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	4	4
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	4
Total gains (losses) (realized/unrealized):
Included in earnings	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Other invested assets | 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
Other invested 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 invested 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
Other invested 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	8,539,671	5,600,008
Purchases	266,951	235,378
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	20,214,824	6,468,704
Total gains (losses) (realized/unrealized):
Included in earnings	11,408,202	633,318
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	11,508,908	677,444
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	11,408,202	633,318
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	11,508,908	677,444
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
Reinsurance recoverables | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	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	3,135	9,261
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(1,579)	(1,580)
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	1,575	7,792
Total gains (losses) (realized/unrealized):
Included in earnings	19	111
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0
Receivables from parents and affiliates | 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
Receivables from parents and affiliates | 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
Receivables from parents and affiliates | 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
Receivables from parents and affiliates | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	19	111
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(8,529,566)	(5,588,840)
Purchases	0	0
Sales	0	0
Issuances	(264,988)	(233,435)
Settlements	0	0
Other	0	0
Transfers Into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(20,196,457)	(6,459,377)
Total gains (losses) (realized/unrealized):
Included in earnings	(11,401,903)	(637,102)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(11,502,609)	(681,227)
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(11,401,903)	(637,102)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(11,502,609)	(681,227)
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
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	(962,351)	(13,015)
Purchases	0	0
Sales	0	0
Issuances	(55,565)	0
Settlements	0	(6,507)
Other	0	0
Transfers Into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(900,261)	(53,136)
Total gains (losses) (realized/unrealized):
Included in earnings	117,655	(33,614)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	125,109	(33,614)
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	117,655	(33,614)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	125,109	(33,614)
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
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	(1,779)	(2,402)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,334)	(3,163)
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	(16,776)	164
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(16,346)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	90	99
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	38,671	29,816
Purchases	3,342	2,372
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	42,013	32,188
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 | Foreign government bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	163	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	159
Transfers out of Level 3	0	0
Fair Value, end of period	152	164
Total gains (losses) (realized/unrealized):
Included in earnings	(11)	5
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(11)	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	50,083	56,588
Purchases	7,193	1,331
Sales	(3,680)	(28)
Issuances	0	0
Settlements	(2,958)	(7,097)
Other	0	1
Transfers into Level 3	98,014	7,577
Transfers out of Level 3	0	0
Fair Value, end of period	130,682	54,960
Total gains (losses) (realized/unrealized):
Included in earnings	(17,970)	(3,412)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(17,186)	(3,163)
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	2,001	6,556
Purchases	6,145	0
Sales	0	(1)
Issuances	0	0
Settlements	(224)	(3,979)
Other	0	0
Transfers into Level 3	0	75,960
Transfers out of Level 3	0	0
Fair Value, end of period	7,438	79,804
Total gains (losses) (realized/unrealized):
Included in earnings	(484)	1,268
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(483)	0
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	668	0
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	538	0
Total gains (losses) (realized/unrealized):
Included in earnings	(130)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(130)	0
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	(130)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(130)	0
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
Trading | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	$ 0	$ 0