Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	$ 4,986	$ 5,616	$ 5,247	$ 5,705
Purchases	0	0	0	0
Sales	0	(734)	0	(929)
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	5,242	5,363	5,242	5,363
Total gains (losses) (realized/unrealized):
Included in earnings	256	481	(5)	587
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	256	480	(5)	598
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	256	481	(5)	587
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	256	480	(5)	598
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	0	0	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	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	0	0	0	0
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 | 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
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
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	12,242	0	8,059	0
Purchases	10,338	0	18,134	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(2)	0	(2)	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	27,136	0	27,136	0
Total gains (losses) (realized/unrealized):
Included in earnings	4,558	0	945	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	4,556	0	944	0
Other assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	4,558	0	945	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	4,556	0	944	0
Other 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 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 assets | 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	565,090	283,991	302,814	239,911
Purchases	4,240	4,518	8,563	9,077
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	(1)	0	21,895
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	539,123	339,744	539,123	339,744
Total gains (losses) (realized/unrealized):
Included in earnings	(30,207)	51,236	227,746	68,861
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(26,137)	53,335	232,325	72,829
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(30,207)	51,236	227,746	68,861
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(26,137)	53,335	232,325	72,829
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
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(25,302,654)	(9,316,905)	(11,822,998)	(8,332,474)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(284,426)	(264,465)	(566,610)	(521,806)
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	(23,998,671)	(11,738,480)	(23,998,671)	(11,738,480)
Total gains (losses) (realized/unrealized):
Included in earnings	1,588,409	(2,157,110)	(11,609,063)	(2,884,200)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,421,382	(2,240,816)	(11,807,482)	(3,025,994)
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	1,588,409	(2,157,110)	(11,609,063)	(2,884,200)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,421,382	(2,240,816)	(11,807,482)	(3,025,994)
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	(158,920)	(80,579)	(196,892)	(42,350)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(28,057)	(35,428)	(50,514)	(65,674)
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	(226,072)	(121,102)	(226,072)	(121,102)
Total gains (losses) (realized/unrealized):
Included in earnings	(39,095)	(5,095)	21,334	(13,078)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(34,321)	(3,299)	10,084	(11,282)
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(39,095)	(5,095)	21,334	(13,078)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(34,321)	(3,299)	10,084	(11,282)
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	(57)	(1,175)	(167)	(1,900)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(982)	0	(982)	(1,998)
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	8,799	1,473	(6,125)	2,914
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	8,875		(7,191)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	18	99	(3)	138
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	11,458	8,779	10,547	8,132
Purchases	758	601	1,669	1,248
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	12,216	9,380	12,216	9,380
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 | Corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	111,606	84,800	104,267	85,452
Purchases	3,896	4,087	15,173	7,313
Sales	(7,810)	0	(8,965)	0
Issuances	0	0	0	0
Settlements	(3,445)	(16,626)	(5,810)	(22,089)
Other	0	0	0	0
Transfers into Level 3	10,783	815	25,132	1,790
Transfers out of Level 3	(244)	(2,018)	(244)	(2,018)
Fair Value, end of period	123,389	71,071	123,389	71,071
Total gains (losses) (realized/unrealized):
Included in earnings	8,603	13	(6,164)	623
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	7,738	0	(8,042)	(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	24,227	50,258	18,825	9,336
Purchases	0	0	6,145	44,273
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(620)	(339)	(1,075)	(4,386)
Other	0	0	0	0
Transfers into Level 3	0	0	0	551
Transfers out of Level 3	(5,636)	(30,578)	(5,636)	(30,578)
Fair Value, end of period	18,128	19,725	18,128	19,725
Total gains (losses) (realized/unrealized):
Included in earnings	157	384	(131)	529
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	155	0	(131)	(2)
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	3,593	0	4,464	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	5,021	0	5,021
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	4,301	4,044	4,301	4,044
Total gains (losses) (realized/unrealized):
Included in earnings	708	(977)	(163)	(977)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	713	(972)	(153)	(972)
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	713	(972)	(153)	(972)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	713	(972)	(153)	(972)
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	$ (5)	$ (5)	$ (10)	$ (5)