Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 299,154	$ 311,853
Estimated Fair Value Assets	11,866	10,084
Estimated Fair Value Liabilities	4,229	3,737
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	60,723	59,290
Estimated Fair Value Assets	5,432	4,572
Estimated Fair Value Liabilities	2,222	1,761
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	6,228	6,009
Estimated Fair Value Assets	3,256	2,684
Estimated Fair Value Liabilities	82	59
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,186	2,369
Estimated Fair Value Assets	3,224	2,667
Estimated Fair Value Liabilities	4	2
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,106	1,304
Estimated Fair Value Assets	8	16
Estimated Fair Value Liabilities	78	17
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,936	2,336
Estimated Fair Value Assets	24	1
Estimated Fair Value Liabilities	0	40
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	50,731	48,022
Estimated Fair Value Assets	2,106	1,855
Estimated Fair Value Liabilities	2,137	1,601
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	4,750	3,675
Estimated Fair Value Assets	44	145
Estimated Fair Value Liabilities	0	27
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	7,377	7,364
Estimated Fair Value Assets	513	83
Estimated Fair Value Liabilities	120	144
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	38,604	36,983
Estimated Fair Value Assets	1,549	1,627
Estimated Fair Value Liabilities	2,017	1,430
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,764	5,259
Estimated Fair Value Assets	70	33
Estimated Fair Value Liabilities	3	101
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	164	1,059
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	3	10
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,600	4,200
Estimated Fair Value Assets	70	33
Estimated Fair Value Liabilities	0	91
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	238,431	252,563
Estimated Fair Value Assets	6,434	5,512
Estimated Fair Value Liabilities	2,007	1,976
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	49,561	58,083
Estimated Fair Value Assets	3,683	2,867
Estimated Fair Value Liabilities	38	185
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	351	129
Estimated Fair Value Assets	0	1
Estimated Fair Value Liabilities	10	2
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate floors
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	12,701	12,701
Estimated Fair Value Assets	350	155
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate caps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	40,730	42,622
Estimated Fair Value Assets	13	18
Estimated Fair Value Liabilities	0	5
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate futures
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,498	2,423
Estimated Fair Value Assets	0	2
Estimated Fair Value Liabilities	2	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	17,746	27,344
Estimated Fair Value Assets	502	764
Estimated Fair Value Liabilities	5	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Synthetic GICs
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	38,646	30,341
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	13,265	13,699
Estimated Fair Value Assets	603	644
Estimated Fair Value Liabilities	693	461
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	15,643	13,507
Estimated Fair Value Assets	209	50
Estimated Fair Value Liabilities	310	393
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Currency futures
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	914	880
Estimated Fair Value Assets	3	7
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Currency options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,350	1,801
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,978	2,944
Estimated Fair Value Assets	9	4
Estimated Fair Value Liabilities	121	102
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	9,609	11,520
Estimated Fair Value Assets	196	272
Estimated Fair Value Liabilities	0	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity futures
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	5,427	4,540
Estimated Fair Value Assets	14	6
Estimated Fair Value Liabilities	38	8
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity index options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	22,954	27,105
Estimated Fair Value Assets	834	694
Estimated Fair Value Liabilities	437	677
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity variance swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	716	1,115
Estimated Fair Value Assets	15	23
Estimated Fair Value Liabilities	12	19
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Total rate of return swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,048	1,048
Estimated Fair Value Assets	0	5
Estimated Fair Value Liabilities	59	49
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity Total Return Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,294	761
Estimated Fair Value Assets	3	0
Estimated Fair Value Liabilities	$ 282	$ 70