Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Gross Notional Amount	$ 303,578	$ 307,459
Estimated Fair Value Assets	8,822	8,969
Estimated Fair Value Liabilities	3,816	3,930
Derivatives Designated as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	51,563	54,384
Estimated Fair Value Assets	4,095	4,225
Estimated Fair Value Liabilities	1,894	2,297
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,808	5,819
Estimated Fair Value Assets	2,390	2,279
Estimated Fair Value Liabilities	41	20
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,421	2,446
Estimated Fair Value Assets	2,355	2,197
Estimated Fair Value Liabilities	2	2
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,380	1,233
Estimated Fair Value Assets	34	54
Estimated Fair Value Liabilities	9	0
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,007	2,140
Estimated Fair Value Assets	1	28
Estimated Fair Value Liabilities	30	18
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	41,793	42,468
Estimated Fair Value Assets	1,684	1,939
Estimated Fair Value Liabilities	1,721	2,048
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,882	3,515
Estimated Fair Value Assets	164	143
Estimated Fair Value Liabilities	6	1
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,935	3,022
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	117	216
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	34,976	35,931
Estimated Fair Value Assets	1,520	1,796
Estimated Fair Value Liabilities	1,598	1,831
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,962	6,097
Estimated Fair Value Assets	21	7
Estimated Fair Value Liabilities	132	229
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	782	960
Estimated Fair Value Assets	9	4
Estimated Fair Value Liabilities	35	27
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,180	5,137
Estimated Fair Value Assets	12	3
Estimated Fair Value Liabilities	97	202
Derivatives Not Designated or Not Qualifying as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	252,015	253,075
Estimated Fair Value Assets	4,727	4,744
Estimated Fair Value Liabilities	1,922	1,633
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,331	54,891
Estimated Fair Value Assets	2,144	1,796
Estimated Fair Value Liabilities	145	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	2	1
Estimated Fair Value Liabilities	11	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	106	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	51,138	54,575
Estimated Fair Value Assets	82	154
Estimated Fair Value Liabilities	0	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,099	2,353
Estimated Fair Value Assets	0	1
Estimated Fair Value Liabilities	4	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	26,689	26,690
Estimated Fair Value Assets	532	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	44	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	26,501	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	13,109	11,388
Estimated Fair Value Assets	830	884
Estimated Fair Value Liabilities	618	458
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	13,064	13,417
Estimated Fair Value Assets	58	198
Estimated Fair Value Liabilities	264	213
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	860	847
Estimated Fair Value Assets	0	4
Estimated Fair Value Liabilities	3	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,980	2,040
Estimated Fair Value Assets	4	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	2,248	1,903
Estimated Fair Value Assets	17	25
Estimated Fair Value Liabilities	63	39
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Gross Notional Amount	11,409	11,391
Estimated Fair Value Assets	198	95
Estimated Fair Value Liabilities	3	13
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,687	2,992
Estimated Fair Value Assets	3	13
Estimated Fair Value Liabilities	18	77
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity index options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	27,880	27,707
Estimated Fair Value Assets	663	884
Estimated Fair Value Liabilities	649	550
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity variance swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,269	2,269
Estimated Fair Value Assets	43	40
Estimated Fair Value Liabilities	92	87
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	767	929
Estimated Fair Value Assets	1	91
Estimated Fair Value Liabilities	$ 52	$ 0