Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional	$ 238,278,370	$ 200,749,958
Assets	7,426,465	14,819,236
Liabilities	(14,307,015)	(11,952,846)
Future policy benefits
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	(10,512,000)	(17,314,000)
Policyholders' account balances
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	(986,000)	(580,000)
Other assets
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	63,000	54,000
Other liabilities
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	(21,000)	(35,000)
Reinsurance Recoverables (Payables)
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	332,000	471,000
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Notional	1,403,565	1,376,290
Assets	24,141	23,167
Liabilities	(71,345)	(82,625)
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Notional	1,403,565	1,376,290
Assets	24,141	23,167
Liabilities	(71,345)	(82,625)
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Notional	236,874,805	199,373,668
Assets	7,402,324	14,796,069
Liabilities	(14,235,670)	(11,870,221)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Futures
Derivative [Line Items]
Notional	4,713,300	4,597,200
Assets	3,401	2,755
Liabilities	(7,564)	(1,621)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Notional	154,911,591	131,129,200
Assets	6,599,563	12,448,036
Liabilities	(12,720,544)	(9,540,941)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Options
Derivative [Line Items]
Notional	10,148,000	10,198,000
Assets	111,391	608,538
Liabilities	(166,887)	(178,563)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Forwards
Derivative [Line Items]
Notional	505,000	75,000
Assets	3,337	464
Liabilities	(24,254)	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Notional	36,228	34,988
Assets	200	4
Liabilities	(100)	(557)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Notional	253,453	228,117
Assets	7,818	7,939
Liabilities	(7,457)	(8,440)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swap
Derivative [Line Items]
Notional	1,095,000	1,574,173
Assets	25,852	38,875
Liabilities	(19)	(52)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Futures
Derivative [Line Items]
Notional	4,459,416	5,558,882
Assets	20,678	9,424
Liabilities	(2,374)	(24,688)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Total Return Swaps
Derivative [Line Items]
Notional	19,541,904	22,121,729
Assets	121,378	62,362
Liabilities	(450,633)	(1,162,907)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Notional	41,210,913	23,856,379
Assets	508,706	1,617,672
Liabilities	$ (855,838)	$ (952,452)