Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fixed Maturities Available-For-Sale | U.S. Treasury securities and obligations of U.S. government authorities and agencies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 0
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0
Net investment income	0
Purchases	4,264
Sales	0
Issuances	0
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	0
Other	973
Fair Value, end of period	5,237	$ 0
Fixed Maturities Available-For-Sale | U.S. Treasury securities and obligations of U.S. government authorities and agencies | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0
Net unrealized investment gains (losses):
Included in earnings	0
Fixed Maturities Available-For-Sale | U.S. Treasury securities and obligations of U.S. government authorities and agencies | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0
Net unrealized investment gains (losses):
Included in earnings	0
Fixed Maturities Available-For-Sale | Foreign government bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	87	0
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	(8)	$ 0
Net investment income	0	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	95
Transfers out of Level 3	(87)	0
Other	0	0
Fair Value, end of period	0	87	0
Fixed Maturities Available-For-Sale | Foreign government bonds | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Fixed Maturities Available-For-Sale | Foreign government bonds | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Fixed Maturities Available-For-Sale | Corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	151,989	127,308
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	(3,627)	2,313	(3,039)
Net investment income	7,874	5,835	5,274
Purchases	17,920	22,871
Sales	(15,283)	(105)
Issuances	0	0
Settlements	(111,675)	(9,085)
Transfers into Level 3	64,412	19,694
Transfers out of Level 3	(5,370)	(12,854)
Other	(4,157)	0
Fair Value, end of period	95,206	151,989	127,308
Fixed Maturities Available-For-Sale | Corporate securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(6,877)	(3,988)	46
Net unrealized investment gains (losses):
Included in earnings	(6,498)	(4,917)	0
Fixed Maturities Available-For-Sale | Corporate securities | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Fixed Maturities Available-For-Sale | Asset-Backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	31,735	46,493
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	217	161	(170)
Net investment income	183	139	49
Purchases	237,469	72,939
Sales	(5,613)	(6,739)
Issuances	0	0
Settlements	(55,184)	(540)
Transfers into Level 3	106,034	34,984
Transfers out of Level 3	(130,059)	(115,676)
Other	0	0
Fair Value, end of period	185,358	31,735	46,493
Fixed Maturities Available-For-Sale | Asset-Backed Securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	576	(26)	9
Net unrealized investment gains (losses):
Included in earnings	(8)	(26)	0
Fixed Maturities Available-For-Sale | Asset-Backed Securities | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Trading account assets | Asset-Backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	0
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0
Net investment income	0	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	(2,634)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Other	0	2,795
Fair Value, end of period	0	0	0
Trading account assets | Asset-Backed Securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Trading account assets | Asset-Backed Securities | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	(161)	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Trading account assets | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	4,864	0
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0
Net investment income	0	0	0
Purchases	0	3,422
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Other	4,205	1,565
Fair Value, end of period	9,758	4,864	0
Trading account assets | Equity securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Trading account assets | Equity securities | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	689	(123)	0
Net unrealized investment gains (losses):
Included in earnings	338	(123)	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	0
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	351	(351)	0
Net investment income	0	0	0
Purchases	0	351
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Other	(351)	0
Fair Value, end of period	0	0	0
Equity securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Equity securities | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	450	450
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0
Net investment income	0	0	0
Purchases	94	0
Sales	(5)	0
Issuances	0	0
Settlements	(2)	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Other	(450)	0
Fair Value, end of period	87	450	450
Short-term Investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Short-term Investments | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Cash equivalents
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	375	225
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0
Net investment income	0	0	0
Purchases	0	150
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Other	(375)	0
Fair Value, end of period	0	375	225
Cash equivalents | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Cash equivalents | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Other long-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	1,565
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0
Net investment income	0	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Other	154	(1,565)
Fair Value, end of period	147	0	1,565
Other long-term investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(7)	0	1,405
Net unrealized investment gains (losses):
Included in earnings	(7)	0	1,405
Other long-term investments | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Reinsurance Recoverables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	240,091	3,012,653
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0
Net investment income	0	0	0
Purchases	19,416	70,448
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Other	2,739	9,578
Fair Value, end of period	244,006	240,091	3,012,653
Reinsurance Recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(18,240)	(2,852,588)	(212,035)
Net unrealized investment gains (losses):
Included in earnings	(10,303)	59,501	(117,840)
Reinsurance Recoverables | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Receivables from Parent and Affiliates
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	33,962	7,664
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	50	(264)
Net investment income	0	0	1
Purchases	0	34,000
Sales	0	(1,987)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	(33,962)	(2,957)
Other	0	(2,795)
Fair Value, end of period	0	33,962	7,664
Receivables from Parent and Affiliates | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	(13)	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Receivables from Parent and Affiliates | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0
Future Policy Benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	(7,707,333)	(3,134,077)
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0
Net investment income	0	0	0
Purchases	0	0
Sales	0	0
Issuances	(996,616)	(781,497)
Settlements	0	0
Transfers Into Level 3	0	0
Transfers out of Level 3	0	0
Other	0	0
Fair Value, end of period	(8,151,902)	(7,707,333)	(3,134,077)
Future Policy Benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	552,047	(3,791,759)	217,101
Net unrealized investment gains (losses):
Included in earnings	307,529	(3,740,535)	119,609
Future Policy Benefits | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0
Net unrealized investment gains (losses):
Included in earnings	$ 0	$ 0	$ 0