Derivatives and Hedging (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Derivative [Line Items]
Gross Notional	$ 421,007,240	$ 358,596,065
Assets	16,348,475	15,332,694
Liabilities	(28,878,187)	(27,242,213)
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Gross Notional	3,879,664	3,311,693
Assets	75,646	202,606
Liabilities	(236,690)	(27,732)
Derivatives Designated as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Gross Notional	2,758	2,851
Assets	0	0
Liabilities	(144)	(209)
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Gross Notional	3,876,906	3,308,842
Assets	75,646	202,606
Liabilities	(236,546)	(27,523)
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Gross Notional	417,127,576	355,284,372
Assets	16,272,829	15,130,088
Liabilities	(28,641,497)	(27,214,481)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Gross Notional	192,871,060	174,170,160
Assets	8,183,113	9,029,399
Liabilities	(19,896,687)	(20,888,553)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Future
Derivative [Line Items]
Gross Notional	1,284,300	1,518,400
Assets	5,962	1,967
Liabilities	(2,406)	(1,443)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Gross Notional	1,791,548	1,146,861
Assets	277	30,078
Liabilities	(51,414)	(181)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Gross Notional	881,065	911,850
Assets	8,919	9,606
Liabilities	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Gross Notional	2,355,355	2,285,052
Assets	54,435	164,152
Liabilities	(66,984)	(9,277)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Gross Notional	165,141,355	117,107,059
Assets	6,314,087	4,453,762
Liabilities	(5,610,158)	(3,717,637)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Option
Derivative [Line Items]
Gross Notional	26,245,000	29,135,000
Assets	111,829	279,414
Liabilities	(1,220,715)	(1,406,265)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Forward
Derivative [Line Items]
Gross Notional	0	0
Assets	0	0
Liabilities	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Total Return Swap
Derivative [Line Items]
Gross Notional	21,237,575	23,025,217
Assets	1,588,928	1,160,080
Liabilities	(1,778,588)	(1,182,913)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Future
Derivative [Line Items]
Gross Notional	943,691	1,802,205
Assets	2,576	15
Liabilities	(242)	(6,060)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Synthetic Gics
Derivative [Line Items]
Gross Notional	4,153,333	3,958,847
Assets	50	143
Liabilities	(14,303)	(31)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Total Return Swaps
Derivative [Line Items]
Gross Notional	223,294	223,721
Assets	2,653	1,472
Liabilities	$ 0	$ (2,121)