Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Derivative [Line Items]
Derivative, Notional Amount	$ 313,927,969	$ 266,639,029
Assets	11,614,703	9,045,737
Liabilities	(22,038,424)	(21,248,026)
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Derivative, Notional Amount	2,928,438	2,277,700
Assets	124,918	121,243
Liabilities	(75,156)	(54,282)
Derivatives Designated as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,897	3,064
Assets	135	0
Liabilities	(330)	(238)
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,925,541	2,274,636
Assets	124,783	121,243
Liabilities	(74,826)	(54,044)
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Derivative, Notional Amount	310,999,531	264,361,329
Assets	11,489,785	8,924,494
Liabilities	(21,963,268)	(21,193,744)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Derivative, Notional Amount	170,060,664	163,179,764
Assets	6,211,118	6,605,817
Liabilities	(17,190,863)	(17,820,436)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Future
Derivative [Line Items]
Derivative, Notional Amount	931,500	1,332,600
Assets	3,371	3,055
Liabilities	(907)	(210)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Derivative, Notional Amount	910,981	744,576
Assets	215	1,772
Liabilities	(13,658)	(12,232)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Derivative, Notional Amount	945,641	643,280
Assets	8,110	7,727
Liabilities	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,255,074	2,237,331
Assets	71,157	96,618
Liabilities	(34,591)	(31,294)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Derivative, Notional Amount	84,822,485	49,247,510
Assets	4,131,807	1,600,335
Liabilities	(2,682,831)	(1,552,706)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Option
Derivative [Line Items]
Derivative, Notional Amount	29,328,000	29,738,000
Assets	159,714	189,112
Liabilities	(963,537)	(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	16,690	741
Liabilities	(19,240)	(3,196)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Total Return Swap
Derivative [Line Items]
Derivative, Notional Amount	18,213,679	15,049,993
Assets	884,499	418,084
Liabilities	(1,056,653)	(803,452)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Future
Derivative [Line Items]
Derivative, Notional Amount	860,469	418,973
Assets	2,310	1,232
Liabilities	(294)	(500)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Synthetic Gics
Derivative [Line Items]
Derivative, Notional Amount	1,213,038	311,302
Assets	794	1
Liabilities	$ (694)	$ 0