Derivative Instruments (Financial Statement Classification and Impact of Derivatives Used in Qualifying and Non-qualifying Hedge Relationships) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	$ (890,952)	$ (6,465)	$ (2,231,880)	$ 626,655
Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	2,977	2,085	5,710	3,700
Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	1,973	10,567	418	6,518
Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	1,882	14,699	3,505	1,727
Derivatives Designated as Hedge Accounting Instruments: | Cash flow hedges | Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	(399)	160	(720)	(678)
Derivatives Designated as Hedge Accounting Instruments: | Cash flow hedges | Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	2,977	2,085	5,710	3,700
Derivatives Designated as Hedge Accounting Instruments: | Cash flow hedges | Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	1,956	10,483	398	6,489
Derivatives Designated as Hedge Accounting Instruments: | Cash flow hedges | Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	1,882	14,699	3,505	1,727
Derivatives Designated as Hedge Accounting Instruments: | Cash flow hedges | Currency/Interest Rate | Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	(399)	160	(720)	(678)
Derivatives Designated as Hedge Accounting Instruments: | Cash flow hedges | Currency/Interest Rate | Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	2,977	2,085	5,710	3,700
Derivatives Designated as Hedge Accounting Instruments: | Cash flow hedges | Currency/Interest Rate | Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	1,956	10,483	398	6,489
Derivatives Designated as Hedge Accounting Instruments: | Cash flow hedges | Currency/Interest Rate | Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	1,882	14,699	3,505	1,727
Derivatives Not Qualifying as Hedge Accounting Instruments: | Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	(890,553)	(6,625)	(2,231,160)	627,333
Derivatives Not Qualifying as Hedge Accounting Instruments: | Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	17	84	20	29
Derivatives Not Qualifying as Hedge Accounting Instruments: | Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate | Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	1,764,300	(404,238)	2,756,745	(1,588,033)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate | Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate | Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate | Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Currency | Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	435	794	248	324
Derivatives Not Qualifying as Hedge Accounting Instruments: | Currency | Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Currency | Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Currency | Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Currency/Interest Rate | Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	6,784	17,228	8,616	4,734
Derivatives Not Qualifying as Hedge Accounting Instruments: | Currency/Interest Rate | Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Currency/Interest Rate | Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	17	84	20	29
Derivatives Not Qualifying as Hedge Accounting Instruments: | Currency/Interest Rate | Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Risk Contract | Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	1,579	0	1,577	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Risk Contract | Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Risk Contract | Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Risk Contract | Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity | Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	(583,113)	(251,520)	(2,233,223)	(239,454)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity | Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity | Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity | Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Embedded Derivatives | Realized Investment Gains (Losses)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	(2,080,538)	631,111	(2,765,123)	2,449,762
Derivatives Not Qualifying as Hedge Accounting Instruments: | Embedded Derivatives | Net Investment Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Embedded Derivatives | Other Income
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	0	0	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Embedded Derivatives | Accumulated Other Comprehensive Income (Loss)
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain (Loss) Recognized In Income Net	$ 0	$ 0	$ 0	$ 0