Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Derivative [Line Items]
Assets	$ 7,355,296	$ 7,086,534
Liabilities	(14,504,013)	(12,573,983)
Derivative, Notional Amount	203,740,296	187,608,681
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Assets	156,102	37,314
Liabilities	(199)	(6,900)
Derivative, Notional Amount	1,379,698	889,896
Derivatives Designated as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Assets	0	55
Liabilities	(190)	0
Derivative, Notional Amount	3,267	3,344
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Assets	156,102	37,259
Liabilities	(9)	(6,900)
Derivative, Notional Amount	1,376,431	886,552
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Assets	7,199,194	7,049,220
Liabilities	(14,503,814)	(12,567,083)
Derivative, Notional Amount	202,360,598	186,718,785
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Assets	5,468,843	5,698,740
Liabilities	(13,071,332)	(10,348,130)
Derivative, Notional Amount	135,289,710	130,358,860
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Future
Derivative [Line Items]
Assets	34,624	2,876
Liabilities	(14,782)	(2,709)
Derivative, Notional Amount	1,670,300	4,109,300
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Assets	8,765	842
Liabilities	(605)	(1,063)
Derivative, Notional Amount	259,344	119,653
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Assets	0	24,789
Liabilities	(3,238)	0
Derivative, Notional Amount	2,079,750	306,900
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Assets	180,430	68,477
Liabilities	(4,517)	(23,251)
Derivative, Notional Amount	1,926,100	2,139,523
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Assets	564,881	902,050
Liabilities	(970,460)	(1,535,272)
Derivative, Notional Amount	36,440,892	19,461,881
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Option
Derivative [Line Items]
Assets	85,071	280,323
Liabilities	(253,193)	(173,863)
Derivative, Notional Amount	9,193,000	9,883,000
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Forward
Derivative [Line Items]
Assets	0	3,760
Liabilities	(5,002)	(991)
Derivative, Notional Amount	115,000	195,000
Derivatives Not Qualifying as Hedge Accounting Instruments: | Total Return Swap
Derivative [Line Items]
Assets	854,969	66,627
Liabilities	(159,232)	(475,209)
Derivative, Notional Amount	12,393,180	15,129,666
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Future
Derivative [Line Items]
Assets	1,611	736
Liabilities	(21,453)	(6,595)
Derivative, Notional Amount	$ 2,993,322	$ 5,015,002