Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional	$ 231,330,687	$ 200,749,958
Assets	7,975,317	14,819,236
Liabilities	(13,149,196)	(11,952,846)
Future policy benefits
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	(12,530,000)	(17,314,000)
Policyholders' account balances
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	(1,361,000)	(580,000)
Other assets
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	68,000	54,000
Other liabilities
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	(31,000)	(35,000)
Reinsurance Recoverables (Payables)
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	366,000	471,000
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Notional	1,776,996	1,376,290
Assets	34,965	23,167
Liabilities	(54,455)	(82,625)
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Notional	1,776,996	1,376,290
Assets	34,965	23,167
Liabilities	(54,455)	(82,625)
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Notional	229,553,691	199,373,668
Assets	7,940,352	14,796,069
Liabilities	(13,094,741)	(11,870,221)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Futures
Derivative [Line Items]
Notional	3,704,500	4,597,200
Assets	3,152	2,755
Liabilities	(157)	(1,621)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Notional	145,129,090	131,129,200
Assets	6,729,984	12,448,036
Liabilities	(11,252,213)	(9,540,941)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Options
Derivative [Line Items]
Notional	10,048,000	10,198,000
Assets	242,653	608,538
Liabilities	(164,917)	(178,563)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Forwards
Derivative [Line Items]
Notional	115,000	75,000
Assets	0	464
Liabilities	(36)	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Notional	38,424	34,988
Assets	155	4
Liabilities	(93)	(557)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Notional	315,652	228,117
Assets	9,050	7,939
Liabilities	(4,034)	(8,440)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swap
Derivative [Line Items]
Notional	1,562,750	1,574,173
Assets	45,970	38,875
Liabilities	0	(52)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Futures
Derivative [Line Items]
Notional	4,236,011	5,558,882
Assets	5,994	9,424
Liabilities	(3,497)	(24,688)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Total Return Swaps
Derivative [Line Items]
Notional	18,299,916	22,121,729
Assets	125,066	62,362
Liabilities	(414,104)	(1,162,907)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Notional	46,104,348	23,856,379
Assets	778,328	1,617,672
Liabilities	$ (1,255,690)	$ (952,452)