Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 337,434	$ 311,853
Estimated Fair Value Assets	18,869	10,084
Estimated Fair Value Liabilities	4,849	3,737
Derivatives Designated as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	60,549	59,290
Estimated Fair Value Assets	8,967	4,572
Estimated Fair Value Liabilities	2,424	1,761
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	6,780	6,009
Estimated Fair Value Assets	3,476	2,684
Estimated Fair Value Liabilities	36	59
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,240	2,369
Estimated Fair Value Assets	3,394	2,667
Estimated Fair Value Liabilities	10	2
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,304	1,304
Estimated Fair Value Assets	71	16
Estimated Fair Value Liabilities	0	17
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,236	2,336
Estimated Fair Value Assets	11	1
Estimated Fair Value Liabilities	26	40
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	49,510	48,022
Estimated Fair Value Assets	5,359	1,855
Estimated Fair Value Liabilities	2,386	1,601
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	5,084	3,675
Estimated Fair Value Assets	181	145
Estimated Fair Value Liabilities	27	27
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	7,239	7,364
Estimated Fair Value Assets	1,037	83
Estimated Fair Value Liabilities	0	144
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	37,187	36,983
Estimated Fair Value Assets	4,141	1,627
Estimated Fair Value Liabilities	2,359	1,430
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	4,259	5,259
Estimated Fair Value Assets	132	33
Estimated Fair Value Liabilities	2	101
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,059	1,059
Estimated Fair Value Assets	67	0
Estimated Fair Value Liabilities	2	10
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,200	4,200
Estimated Fair Value Assets	65	33
Estimated Fair Value Liabilities	0	91
Derivatives Not Designated or Not Qualifying as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	276,885	252,563
Estimated Fair Value Assets	9,902	5,512
Estimated Fair Value Liabilities	2,425	1,976
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	70,027	58,083
Estimated Fair Value Assets	5,127	2,867
Estimated Fair Value Liabilities	711	185
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	130	129
Estimated Fair Value Assets	1	1
Estimated Fair Value Liabilities	2	2
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate floors
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	12,701	12,701
Estimated Fair Value Assets	424	155
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate caps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	55,630	42,622
Estimated Fair Value Assets	22	18
Estimated Fair Value Liabilities	0	5
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate futures
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,514	2,423
Estimated Fair Value Assets	1	2
Estimated Fair Value Liabilities	5	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	27,600	27,344
Estimated Fair Value Assets	1,269	764
Estimated Fair Value Liabilities	0	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,048	1,048
Estimated Fair Value Assets	180	5
Estimated Fair Value Liabilities	0	49
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Synthetic GICs
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	33,588	30,341
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	13,807	13,699
Estimated Fair Value Assets	1,119	644
Estimated Fair Value Liabilities	788	461
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	13,376	13,507
Estimated Fair Value Assets	193	50
Estimated Fair Value Liabilities	428	393
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency futures
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	927	880
Estimated Fair Value Assets	5	7
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,800	1,801
Estimated Fair Value Assets	1	0
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,919	2,944
Estimated Fair Value Assets	43	4
Estimated Fair Value Liabilities	68	102
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	11,353	11,520
Estimated Fair Value Assets	30	272
Estimated Fair Value Liabilities	90	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity futures
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,586	4,540
Estimated Fair Value Assets	28	6
Estimated Fair Value Liabilities	19	8
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity index options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	25,181	27,105
Estimated Fair Value Assets	1,237	694
Estimated Fair Value Liabilities	303	677
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity variance swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	937	1,115
Estimated Fair Value Assets	34	23
Estimated Fair Value Liabilities	11	19
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	761	761
Estimated Fair Value Assets	188	0
Estimated Fair Value Liabilities	$ 0	$ 70