Derivatives and Hedging (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Derivative [Line Items]
Gross Notional	$ 476,879,538	$ 358,596,065
Assets	20,118,548	15,332,694
Liabilities	(31,035,004)	(27,242,213)
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Gross Notional	4,342,177	3,311,693
Assets	88,554	202,606
Liabilities	(213,624)	(27,732)
Derivatives Designated as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Gross Notional	2,711	2,851
Assets	0	0
Liabilities	(126)	(209)
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Gross Notional	4,339,466	3,308,842
Assets	88,554	202,606
Liabilities	(213,498)	(27,523)
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Gross Notional	472,537,361	355,284,372
Assets	20,029,994	15,130,088
Liabilities	(30,821,380)	(27,214,481)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Gross Notional	193,248,460	174,170,160
Assets	8,054,508	9,029,399
Liabilities	(19,736,940)	(20,888,553)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Future
Derivative [Line Items]
Gross Notional	1,817,500	1,518,400
Assets	1,014	1,967
Liabilities	(2,051)	(1,443)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Gross Notional	2,316,193	1,146,861
Assets	10,343	30,078
Liabilities	(7,047)	(181)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Gross Notional	849,950	911,850
Assets	8,742	9,606
Liabilities	0	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Gross Notional	2,225,111	2,285,052
Assets	61,881	164,152
Liabilities	(50,429)	(9,277)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Gross Notional	211,675,759	117,107,059
Assets	9,174,115	4,453,762
Liabilities	(7,346,036)	(3,717,637)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Option
Derivative [Line Items]
Gross Notional	26,725,000	29,135,000
Assets	110,164	279,414
Liabilities	(1,204,126)	(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	28,343,850	23,025,217
Assets	2,602,653	1,160,080
Liabilities	(2,473,843)	(1,182,913)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Future
Derivative [Line Items]
Gross Notional	813,379	1,802,205
Assets	1,692	15
Liabilities	(908)	(6,060)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Synthetic Gics
Derivative [Line Items]
Gross Notional	4,180,490	3,958,847
Assets	0	143
Liabilities	0	(31)
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Total Return Swaps
Derivative [Line Items]
Gross Notional	341,669	223,721
Assets	4,882	1,472
Liabilities	$ 0	$ (2,121)