Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 311,853	$ 307,459
Estimated Fair Value Assets	10,084	8,969
Estimated Fair Value Liabilities	3,737	3,930
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	59,290	54,384
Estimated Fair Value Assets	4,572	4,225
Estimated Fair Value Liabilities	1,761	2,297
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	6,009	5,819
Estimated Fair Value Assets	2,684	2,279
Estimated Fair Value Liabilities	59	20
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,369	2,446
Estimated Fair Value Assets	2,667	2,197
Estimated Fair Value Liabilities	2	2
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,304	1,233
Estimated Fair Value Assets	16	54
Estimated Fair Value Liabilities	17	0
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,336	2,140
Estimated Fair Value Assets	1	28
Estimated Fair Value Liabilities	40	18
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	48,022	42,468
Estimated Fair Value Assets	1,855	1,939
Estimated Fair Value Liabilities	1,601	2,048
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,675	3,515
Estimated Fair Value Assets	145	143
Estimated Fair Value Liabilities	27	1
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	7,364	3,022
Estimated Fair Value Assets	83	0
Estimated Fair Value Liabilities	144	216
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	36,983	35,931
Estimated Fair Value Assets	1,627	1,796
Estimated Fair Value Liabilities	1,430	1,831
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	5,259	6,097
Estimated Fair Value Assets	33	7
Estimated Fair Value Liabilities	101	229
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,059	960
Estimated Fair Value Assets	0	4
Estimated Fair Value Liabilities	10	27
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	4,200	5,137
Estimated Fair Value Assets	33	3
Estimated Fair Value Liabilities	91	202
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	252,563	253,075
Estimated Fair Value Assets	5,512	4,744
Estimated Fair Value Liabilities	1,976	1,633
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	58,083	54,891
Estimated Fair Value Assets	2,867	1,796
Estimated Fair Value Liabilities	185	175
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	129	234
Estimated Fair Value Assets	1	1
Estimated Fair Value Liabilities	2	15
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	155	102
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	42,622	54,575
Estimated Fair Value Assets	18	154
Estimated Fair Value Liabilities	5	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate futures
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,423	2,353
Estimated Fair Value Assets	2	1
Estimated Fair Value Liabilities	3	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	27,344	26,690
Estimated Fair Value Assets	764	416
Estimated Fair Value Liabilities	1	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Synthetic GICs
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	30,341	25,700
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	13,699	11,388
Estimated Fair Value Assets	644	884
Estimated Fair Value Liabilities	461	458
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	13,507	13,417
Estimated Fair Value Assets	50	198
Estimated Fair Value Liabilities	393	213
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Currency futures
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	880	847
Estimated Fair Value Assets	7	4
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	1,801	2,040
Estimated Fair Value Assets	0	7
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	2,944	1,903
Estimated Fair Value Assets	4	25
Estimated Fair Value Liabilities	102	39
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	11,520	11,391
Estimated Fair Value Assets	272	95
Estimated Fair Value Liabilities	1	13
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity futures
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	4,540	2,992
Estimated Fair Value Assets	6	13
Estimated Fair Value Liabilities	8	77
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity index options
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	27,105	27,707
Estimated Fair Value Assets	694	884
Estimated Fair Value Liabilities	677	550
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity variance swaps
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,115	2,269
Estimated Fair Value Assets	23	40
Estimated Fair Value Liabilities	19	87
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	5	33
Estimated Fair Value Liabilities	49	2
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity Total Return Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	761	929
Estimated Fair Value Assets	0	91
Estimated Fair Value Liabilities	$ 70	$ 0