Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Gross Notional Amount	$ 312,101	$ 307,459
Estimated Fair Value Assets	10,631	8,969
Estimated Fair Value Liabilities	3,323	3,930
Derivatives Designated as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	52,022	54,384
Estimated Fair Value Assets	4,842	4,225
Estimated Fair Value Liabilities	1,582	2,297
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,909	5,819
Estimated Fair Value Assets	2,659	2,279
Estimated Fair Value Liabilities	16	20
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,315	2,446
Estimated Fair Value Assets	2,590	2,197
Estimated Fair Value Liabilities	3	2
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,182	1,233
Estimated Fair Value Assets	41	54
Estimated Fair Value Liabilities	5	0
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,412	2,140
Estimated Fair Value Assets	28	28
Estimated Fair Value Liabilities	8	18
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	42,104	42,468
Estimated Fair Value Assets	2,160	1,939
Estimated Fair Value Liabilities	1,471	2,048
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,792	3,515
Estimated Fair Value Assets	184	143
Estimated Fair Value Liabilities	8	1
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,855	3,022
Estimated Fair Value Assets	39	0
Estimated Fair Value Liabilities	19	216
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	35,457	35,931
Estimated Fair Value Assets	1,937	1,796
Estimated Fair Value Liabilities	1,444	1,831
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	4,009	6,097
Estimated Fair Value Assets	23	7
Estimated Fair Value Liabilities	95	229
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	509	960
Estimated Fair Value Assets	5	4
Estimated Fair Value Liabilities	7	27
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,500	5,137
Estimated Fair Value Assets	18	3
Estimated Fair Value Liabilities	88	202
Derivatives Not Designated or Not Qualifying as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	260,079	253,075
Estimated Fair Value Assets	5,789	4,744
Estimated Fair Value Liabilities	1,741	1,633
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,465	54,891
Estimated Fair Value Assets	2,617	1,796
Estimated Fair Value Liabilities	166	175
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	235	234
Estimated Fair Value Assets	6	1
Estimated Fair Value Liabilities	3	15
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate floors
Derivatives, Fair Value [Line Items]
Gross Notional Amount	12,701	12,701
Estimated Fair Value Assets	186	102
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate caps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	52,388	54,575
Estimated Fair Value Assets	30	154
Estimated Fair Value Liabilities	2	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,786	2,353
Estimated Fair Value Assets	0	1
Estimated Fair Value Liabilities	0	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	30,780	26,690
Estimated Fair Value Assets	932	416
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,048	1,048
Estimated Fair Value Assets	65	33
Estimated Fair Value Liabilities	0	2
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Synthetic GICs
Derivatives, Fair Value [Line Items]
Gross Notional Amount	27,219	25,700
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]
Gross Notional Amount	12,860	11,388
Estimated Fair Value Assets	833	884
Estimated Fair Value Liabilities	466	458
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	14,320	13,417
Estimated Fair Value Assets	108	198
Estimated Fair Value Liabilities	228	213
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	883	847
Estimated Fair Value Assets	0	4
Estimated Fair Value Liabilities	6	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,920	2,040
Estimated Fair Value Assets	1	7
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,483	1,903
Estimated Fair Value Assets	17	25
Estimated Fair Value Liabilities	74	39
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Gross Notional Amount	12,340	11,391
Estimated Fair Value Assets	257	95
Estimated Fair Value Liabilities	1	13
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,946	2,992
Estimated Fair Value Assets	4	13
Estimated Fair Value Liabilities	22	77
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity index options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	27,763	27,707
Estimated Fair Value Assets	692	884
Estimated Fair Value Liabilities	666	550
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity variance swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,173	2,269
Estimated Fair Value Assets	41	40
Estimated Fair Value Liabilities	94	87
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	769	929
Estimated Fair Value Assets	0	91
Estimated Fair Value Liabilities	$ 13	$ 0