Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Derivative [Line Items]
Derivative, Notional Amount	$ 311,249,267	$ 196,977,180
Assets	8,298,627	7,685,050
Liabilities	(19,766,950)	(18,654,072)
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Derivative, Notional Amount	2,011,367	1,936,568
Assets	184,327	233,812
Liabilities	(21,284)	(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	(281)	(316)
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,005,195	1,933,343
Assets	184,327	233,812
Liabilities	(21,003)	(10,462)
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Derivative, Notional Amount	309,237,900	195,040,612
Assets	8,114,300	7,451,238
Liabilities	(19,745,666)	(18,643,294)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Derivative, Notional Amount	225,661,110	138,419,110
Assets	6,500,268	6,757,890
Liabilities	(17,340,905)	(17,092,749)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Future
Derivative [Line Items]
Derivative, Notional Amount	1,397,200	2,425,500
Assets	426	3,267
Liabilities	(7,675)	(201)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Derivative, Notional Amount	730,882	364,946
Assets	4,847	590
Liabilities	(3,563)	(10,423)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Derivative, Notional Amount	89,631	47,450
Assets	1,973	346
Liabilities	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Derivative, Notional Amount	2,345,911	2,289,170
Assets	152,240	194,412
Liabilities	(16,276)	(14,624)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Derivative, Notional Amount	40,732,315	25,187,516
Assets	1,081,712	239,003
Liabilities	(1,212,176)	(1,112,196)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Option
Derivative [Line Items]
Derivative, Notional Amount	23,248,000	8,368,000
Assets	107,941	123,168
Liabilities	(693,225)	(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	4,668	11,265
Liabilities	(6,719)	(12,359)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Total Return Swap
Derivative [Line Items]
Derivative, Notional Amount	13,186,165	15,958,130
Assets	255,586	120,341
Liabilities	(464,354)	(175,104)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Future
Derivative [Line Items]
Derivative, Notional Amount	742,686	876,790
Assets	4,639	956
Liabilities	$ (773)	$ (513)