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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
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	$ 980	$ 0	$ 0	$ 0
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0	0
Net investment income	0	0	0	0
Purchases	2,170	0	2,176	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Other	1	0	975	0
Fair Value, end of period	3,151	0	3,151	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	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	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	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	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	0	0	87	0
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0	0
Net investment income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	(87)	0
Other	0	0	0	0
Fair Value, end of period	0	0	0	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	0
Net unrealized investment gains (losses):
Included in earnings	0	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	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Fixed Maturities Available-For-Sale | U.S. Corporate Public Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	1,281	15,000	15,598	15,000
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	(14)	0	(15)	0
Net investment income	7	0	15	0
Purchases	0	0	0	0
Sales	0	0	(14,026)	0
Issuances	0	0	0	0
Settlements	(302)	0	(664)	0
Transfers into Level 3	935	0	2,350	0
Transfers out of Level 3	0	0	(377)	0
Other	0	0	(974)	0
Fair Value, end of period	1,911	15,000	1,911	15,000
Fixed Maturities Available-For-Sale | U.S. Corporate Public Securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	4	0	4	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Fixed Maturities Available-For-Sale | U.S. Corporate Public Securities | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Fixed Maturities Available-For-Sale | U.S. Corporate Private Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	127,492	116,844	124,864	107,777
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	986	(1,450)	(110)	(2,887)
Net investment income	1,466	1,400	4,819	2,781
Purchases	578	11,108	1,042	11,227
Sales	(341)	0	(341)	0
Issuances	0	0	0	0
Settlements	(5,432)	(214)	(5,629)	(424)
Transfers into Level 3	0	0	0	10,176
Transfers out of Level 3	0	(1,015)	0	(1,015)
Other	0	0	0	0
Fair Value, end of period	122,609	126,673	122,609	126,673
Fixed Maturities Available-For-Sale | U.S. Corporate Private Securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(2,140)	0	(2,036)	(962)
Net unrealized investment gains (losses):
Included in earnings	(2,194)	0	(2,194)	(962)
Fixed Maturities Available-For-Sale | U.S. Corporate Private Securities | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Fixed Maturities Available-For-Sale | Foreign Corporate Private Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	12,064	8,989	11,527	4,531
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	196	3,525	776	987
Net investment income	9	77	23	127
Purchases	26	1,991	52	1,990
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	(1,739)
Transfers into Level 3	0	0	0	8,686
Transfers out of Level 3	(3,248)	0	(3,248)	0
Other	0	0	0	0
Fair Value, end of period	9,047	14,582	9,047	14,582
Fixed Maturities Available-For-Sale | Foreign Corporate Private Securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	(83)	0
Net unrealized investment gains (losses):
Included in earnings	0	0	(83)	0
Fixed Maturities Available-For-Sale | Foreign Corporate Private Securities | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	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	148,869	62,719	31,735	46,493
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	111	263	271	38
Net investment income	28	34	52	88
Purchases	99,159	54,119	150,607	54,119
Sales	(1,595)	(250)	(1,595)	(250)
Issuances	0	0	0	0
Settlements	(42,510)	(48)	(42,552)	(488)
Transfers into Level 3	26,921	0	92,466	17,824
Transfers out of Level 3	(15,489)	(29,468)	(15,489)	(30,455)
Other	0	0	0	0
Fair Value, end of period	215,503	87,371	215,503	87,371
Fixed Maturities Available-For-Sale | Asset-Backed Securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	9	2	8	2
Net unrealized investment gains (losses):
Included in earnings	0	0	(1)	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	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Trading account assets | Equity Securities, Available-For-Sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	5,441	2,036	4,864	0
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0	0
Net investment income	0	0	0	0
Purchases	0	3,423	0	3,423
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Other	1	0	352	1,565
Fair Value, end of period	5,854	5,076	5,854	5,076
Trading account assets | Equity Securities, Available-For-Sale | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Trading account assets | Equity Securities, Available-For-Sale | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	412	(383)	638	88
Net unrealized investment gains (losses):
Included in earnings	61	(383)	287	88
Equity Securities, Available-For-Sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	0	0	0	0
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	351	0
Net investment income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Other	0	0	(351)	0
Fair Value, end of period	0	0	0	0
Equity Securities, Available-For-Sale | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Equity Securities, Available-For-Sale | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	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	450	450
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0	0
Net investment income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Other	0	0	0	0
Fair Value, end of period	450	450	450	450
Short-term investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Short-term investments | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Cash equivalents
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	375	375	375	225
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0	0
Net investment income	0	0	0	0
Purchases	0	0	0	150
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Other	0	0	0	0
Fair Value, end of period	375	375	375	375
Cash equivalents | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Cash equivalents | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	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	0	0	1,565
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0	0
Net investment income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Other	0	0	0	(1,565)
Fair Value, end of period	0	0	0	0
Other Long- term Investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Other Long- term Investments | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
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	218,531	3,693,262	240,091	3,012,653
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0	0
Net investment income	0	0	0	0
Purchases	4,911	4,931	9,784	60,566
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Other	3,834	0	(2,483)	0
Fair Value, end of period	268,337	345,918	268,337	345,918
Reinsurance Recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	41,061	(3,352,275)	20,945	(2,727,301)
Net unrealized investment gains (losses):
Included in earnings	43,088	35,619	24,869	90,507
Reinsurance Recoverables | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	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	0	2,847	33,962	7,664
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	(71)	0	69
Net investment income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	(2,000)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	(33,962)	(2,957)
Other	0	0	0	0
Fair Value, end of period	0	2,776	0	2,776
Receivables From Parents And Affiliates | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	0	0	0	0
Receivables From Parents And Affiliates | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
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	(7,169,218)	(3,842,607)	(7,707,333)	(3,134,077)
Total gains (losses) (realized/unrealized):
Included in other comprehensive income (loss)	0	0	0	0
Net investment income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(248,909)	(235,472)	(495,258)	(293,972)
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Other(5)	0	0	0	0
Fair Value, end of period	(9,331,040)	(12,326,533)	(9,331,040)	(12,326,533)
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(1,912,913)	(8,248,454)	(1,128,449)	(8,898,484)
Net unrealized investment gains (losses):
Included in earnings	(1,972,296)	(8,060,058)	(1,246,436)	(8,526,179)
Future policy benefits | Asset management fees and other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Net unrealized investment gains (losses):
Included in earnings	$ 0	$ 0	$ 0	$ 0