Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Gross Notional Amount	$ 307,459	$ 275,916
Estimated Fair Value Assets	8,969	8,551
Estimated Fair Value Liabilities	3,930	4,339
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,384	57,020
Estimated Fair Value Assets	4,225	3,764
Estimated Fair Value Liabilities	2,297	2,023
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,819	8,212
Estimated Fair Value Assets	2,279	2,341
Estimated Fair Value Liabilities	20	58
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,446	3,843
Estimated Fair Value Assets	2,197	2,289
Estimated Fair Value Liabilities	2	3
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,233	1,116
Estimated Fair Value Assets	54	50
Estimated Fair Value Liabilities	0	18
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,140	3,253
Estimated Fair Value Assets	28	2
Estimated Fair Value Liabilities	18	37
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	42,468	39,068
Estimated Fair Value Assets	1,939	1,377
Estimated Fair Value Liabilities	2,048	1,797
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,515	3,584
Estimated Fair Value Assets	143	235
Estimated Fair Value Liabilities	1	4
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,022	3,332
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	216	128
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	35,931	32,152
Estimated Fair Value Assets	1,796	1,142
Estimated Fair Value Liabilities	1,831	1,665
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	6,097	9,740
Estimated Fair Value Assets	7	46
Estimated Fair Value Liabilities	229	168
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	960	332
Estimated Fair Value Assets	4	2
Estimated Fair Value Liabilities	27	5
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,137	9,408
Estimated Fair Value Assets	3	44
Estimated Fair Value Liabilities	202	163
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	253,075	218,896
Estimated Fair Value Assets	4,744	4,787
Estimated Fair Value Liabilities	1,633	2,316
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,891	60,485
Estimated Fair Value Assets	1,796	2,203
Estimated Fair Value Liabilities	175	576
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	234	217
Estimated Fair Value Assets	1	0
Estimated Fair Value Liabilities	15	42
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate floors
Derivatives, Fair Value [Line Items]
Gross Notional Amount	12,701	7,201
Estimated Fair Value Assets	102	92
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate caps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,575	53,079
Estimated Fair Value Assets	154	78
Estimated Fair Value Liabilities	1	2
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,353	4,366
Estimated Fair Value Assets	1	2
Estimated Fair Value Liabilities	3	4
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	26,690	12,009
Estimated Fair Value Assets	416	656
Estimated Fair Value Liabilities	0	11
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Synthetic GICs
Derivatives, Fair Value [Line Items]
Gross Notional Amount	25,700	11,318
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]
Gross Notional Amount	11,388	9,902
Estimated Fair Value Assets	884	693
Estimated Fair Value Liabilities	458	506
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	13,417	12,238
Estimated Fair Value Assets	198	79
Estimated Fair Value Liabilities	213	190
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Currency futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	847	846
Estimated Fair Value Assets	4	2
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,040	3,123
Estimated Fair Value Assets	7	55
Estimated Fair Value Liabilities	0	6
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,903	2,020
Estimated Fair Value Assets	25	7
Estimated Fair Value Liabilities	39	43
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Gross Notional Amount	11,391	11,375
Estimated Fair Value Assets	95	271
Estimated Fair Value Liabilities	13	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,992	4,005
Estimated Fair Value Assets	13	18
Estimated Fair Value Liabilities	77	4
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity index options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	27,707	19,886
Estimated Fair Value Assets	884	569
Estimated Fair Value Liabilities	550	690
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity variance swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,269	4,661
Estimated Fair Value Assets	40	54
Estimated Fair Value Liabilities	87	199
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Total rate of return swaps [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,048	1,048
Estimated Fair Value Assets	33	8
Estimated Fair Value Liabilities	2	2
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity Total Return Swaps [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	929	1,117
Estimated Fair Value Assets	91	0
Estimated Fair Value Liabilities	$ 0	$ 41