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	$ 5,247	$ 5,705
Purchases	0	0
Sales	0	(195)
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	4,986	5,616
Total gains (losses) (realized/unrealized):
Included in earnings	(261)	106
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(261)	118
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	(261)	106
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(261)	118
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	0	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	0	0
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
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	8,059	0
Purchases	7,796	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	12,242	0
Total gains (losses) (realized/unrealized):
Included in earnings	(3,613)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(3,613)	0
Other assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(3,613)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(3,613)	0
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
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	302,814	239,911
Purchases	4,323	4,559
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	21,896
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	565,090	283,991
Total gains (losses) (realized/unrealized):
Included in earnings	257,953	17,625
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	260,722	17,625
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	257,953	17,625
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	260,722	17,625
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
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(11,822,998)	(8,332,474)
Purchases	0	0
Sales	0	0
Issuances	(282,184)	(257,341)
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(25,302,654)	(9,316,905)
Total gains (losses) (realized/unrealized):
Included in earnings	(13,197,472)	(727,090)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(13,329,640)	(790,926)
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(13,197,472)	(727,090)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(13,329,640)	(790,926)
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	(196,892)	(42,350)
Purchases	0	0
Sales	0	0
Issuances	(22,457)	(30,246)
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(158,920)	(80,579)
Total gains (losses) (realized/unrealized):
Included in earnings	60,429	(7,983)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	53,957	(7,983)
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	60,429	(7,983)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	53,957	(7,983)
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	(110)	(725)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	(1,998)
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	(14,924)	1,441
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(16,067)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	(21)	39
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	10,547	8,132
Purchases	911	647
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	11,458	8,779
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	104,267	85,452
Purchases	11,277	3,226
Sales	1,155	0
Issuances	0	0
Settlements	(2,365)	(5,463)
Other	0	0
Transfers into Level 3	14,349	975
Transfers out of Level 3	0	0
Fair Value, end of period	111,606	84,800
Total gains (losses) (realized/unrealized):
Included in earnings	(14,767)	610
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(15,781)	(1,996)
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	18,825	9,336
Purchases	6,145	44,273
Sales	0	0
Issuances	0	0
Settlements	(455)	(4,047)
Other	0	0
Transfers into Level 3	0	551
Transfers out of Level 3	0	0
Fair Value, end of period	24,227	50,258
Total gains (losses) (realized/unrealized):
Included in earnings	(288)	145
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(286)	(2)
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	4,464	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	3,593	0
Total gains (losses) (realized/unrealized):
Included in earnings	(871)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(866)	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	(866)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(866)	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	$ (5)	$ 0