Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Derivative [Line Items]
Derivative, Notional Amount	$ 296,118,365	$ 266,639,029
Assets	13,054,588	9,045,737
Liabilities	(24,253,329)	(21,248,026)
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Derivative, Notional Amount	2,728,618	2,277,700
Assets	166,088	121,243
Liabilities	(32,736)	(54,282)
Derivatives Designated as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,975	3,064
Assets	215	0
Liabilities	(491)	(238)
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,725,643	2,274,636
Assets	165,873	121,243
Liabilities	(32,245)	(54,044)
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Derivative, Notional Amount	293,389,747	264,361,329
Assets	12,888,500	8,924,494
Liabilities	(24,220,593)	(21,193,744)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Derivative, Notional Amount	167,487,864	163,179,764
Assets	8,227,910	6,605,817
Liabilities	(19,877,550)	(17,820,436)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Future
Derivative [Line Items]
Derivative, Notional Amount	859,000	1,332,600
Assets	2,964	3,055
Liabilities	(291)	(210)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Derivative, Notional Amount	908,100	744,576
Assets	4,913	1,772
Liabilities	(985)	(12,232)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Derivative, Notional Amount	520,600	643,280
Assets	4,830	7,727
Liabilities	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,238,553	2,237,331
Assets	125,477	96,618
Liabilities	(20,687)	(31,294)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Derivative, Notional Amount	72,507,886	49,247,510
Assets	3,638,902	1,600,335
Liabilities	(2,274,561)	(1,552,706)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Option
Derivative [Line Items]
Derivative, Notional Amount	29,503,000	29,738,000
Assets	227,324	189,112
Liabilities	(1,181,463)	(969,718)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Forward
Derivative [Line Items]
Derivative, Notional Amount	1,458,000	1,458,000
Assets	55,415	741
Liabilities	(57,927)	(3,196)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Total Return Swap
Derivative [Line Items]
Derivative, Notional Amount	15,885,233	15,049,993
Assets	599,846	418,084
Liabilities	(803,880)	(803,452)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Future
Derivative [Line Items]
Derivative, Notional Amount	813,292	418,973
Assets	156	1,232
Liabilities	(3,041)	(500)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Synthetic Gics
Derivative [Line Items]
Derivative, Notional Amount	1,208,219	311,302
Assets	763	1
Liabilities	$ (208)	$ 0