Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	$ 11,175	$ 8,080
Estimated Fair Value Liabilities	1,694	2,102
Derivative, Notional Amount	222,382	221,575
Derivatives Designated as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	5,736	4,079
Estimated Fair Value Liabilities	1,249	1,291
Derivative, Notional Amount	41,596	40,977
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	3,350	2,680
Estimated Fair Value Liabilities	33	19
Derivative, Notional Amount	4,206	3,620
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	3,339	2,668
Estimated Fair Value Liabilities	11	2
Derivative, Notional Amount	3,210	2,370
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	11	12
Estimated Fair Value Liabilities	22	17
Derivative, Notional Amount	996	1,250
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	2,386	1,399
Estimated Fair Value Liabilities	1,216	1,272
Derivative, Notional Amount	37,390	37,357
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	47	125
Estimated Fair Value Liabilities	29	27
Derivative, Notional Amount	4,511	3,324
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	707	75
Estimated Fair Value Liabilities	0	142
Derivative, Notional Amount	5,380	6,793
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	1,632	1,199
Estimated Fair Value Liabilities	1,187	1,103
Derivative, Notional Amount	27,499	27,240
Derivatives Not Designated or Not Qualifying as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	5,439	4,001
Estimated Fair Value Liabilities	445	811
Derivative, Notional Amount	180,786	180,598
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate swaps
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	3,328	2,296
Estimated Fair Value Liabilities	50	133
Derivative, Notional Amount	34,800	38,820
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate floors
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	393	156
Estimated Fair Value Liabilities	0	0
Derivative, Notional Amount	12,701	12,701
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate caps
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	12	18
Estimated Fair Value Liabilities	0	5
Derivative, Notional Amount	55,006	42,622
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate futures
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	0	0
Derivative, Notional Amount	72	745
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate options
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	350	427
Estimated Fair Value Liabilities	5	0
Derivative, Notional Amount	19,431	24,944
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Synthetic GICs
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	0	0
Derivative, Notional Amount	13,770	16,498
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	485	419
Estimated Fair Value Liabilities	92	97
Derivative, Notional Amount	5,542	6,124
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	18	12
Estimated Fair Value Liabilities	7	8
Derivative, Notional Amount	1,101	1,001
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	34	4
Estimated Fair Value Liabilities	2	11
Derivative, Notional Amount	895	888
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	93	200
Estimated Fair Value Liabilities	4	1
Derivative, Notional Amount	6,860	8,711
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity futures
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	1	0
Estimated Fair Value Liabilities	13	5
Derivative, Notional Amount	2,499	2,039
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity index options
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	580	447
Estimated Fair Value Liabilities	205	417
Derivative, Notional Amount	23,821	23,104
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity variance swaps
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	13	17
Estimated Fair Value Liabilities	13	17
Derivative, Notional Amount	637	637
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity Total Return Swaps [Member]
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	77	0
Estimated Fair Value Liabilities	46	68
Derivative, Notional Amount	2,603	716
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	55	5
Estimated Fair Value Liabilities	8	49
Derivative, Notional Amount	$ 1,048	$ 1,048