Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Derivative [Line Items]
Derivative, Notional Amount	$ 259,183,785	$ 196,977,180
Assets	12,311,325	7,685,050
Liabilities	(25,816,497)	(18,654,072)
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Derivative, Notional Amount	2,106,980	1,936,568
Assets	187,257	233,812
Liabilities	(18,467)	(10,778)
Derivatives Designated as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Derivative, Notional Amount	6,172	3,225
Assets	0	0
Liabilities	(356)	(316)
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,100,808	1,933,343
Assets	187,257	233,812
Liabilities	(18,111)	(10,462)
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Derivative, Notional Amount	257,076,805	195,040,612
Assets	12,124,068	7,451,238
Liabilities	(25,798,030)	(18,643,294)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Derivative, Notional Amount	160,769,460	138,419,110
Assets	10,293,935	6,757,890
Liabilities	(22,659,077)	(17,092,749)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Future
Derivative [Line Items]
Derivative, Notional Amount	2,557,132	2,425,500
Assets	495	3,267
Liabilities	(5,251)	(201)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Derivative, Notional Amount	929,085	364,946
Assets	18,545	590
Liabilities	(6,270)	(10,423)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Derivative, Notional Amount	144,300	47,450
Assets	885	346
Liabilities	(316)	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,332,940	2,289,170
Assets	167,484	194,412
Liabilities	(15,371)	(14,624)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Derivative, Notional Amount	45,258,330	25,187,516
Assets	805,583	239,003
Liabilities	(1,363,539)	(1,112,196)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Option
Derivative [Line Items]
Derivative, Notional Amount	29,418,000	8,368,000
Assets	311,893	123,168
Liabilities	(1,404,581)	(225,125)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Forward
Derivative [Line Items]
Derivative, Notional Amount	1,104,000	1,104,000
Assets	84,165	11,265
Liabilities	(86,244)	(12,359)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Total Return Swap
Derivative [Line Items]
Derivative, Notional Amount	13,759,916	15,958,130
Assets	440,719	120,341
Liabilities	(253,318)	(175,104)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Future
Derivative [Line Items]
Derivative, Notional Amount	803,642	876,790
Assets	364	956
Liabilities	$ (4,063)	$ (513)