Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gross Notional Amount	$ 452,710	$ 418,148
Estimated Fair Value Assets	12,278	15,761
Estimated Fair Value Liabilities	8,399	10,804
Derivatives Designated as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,508	52,199
Estimated Fair Value Assets	4,616	4,902
Estimated Fair Value Liabilities	2,626	2,803
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	8,202	7,637
Estimated Fair Value Assets	2,279	2,296
Estimated Fair Value Liabilities	255	284
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,176	5,331
Estimated Fair Value Assets	2,237	2,262
Estimated Fair Value Liabilities	6	6
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,221	1,221
Estimated Fair Value Assets	31	34
Estimated Fair Value Liabilities	223	224
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,805	1,085
Estimated Fair Value Assets	11	0
Estimated Fair Value Liabilities	26	54
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	36,444	34,290
Estimated Fair Value Assets	2,305	2,411
Estimated Fair Value Liabilities	2,190	2,469
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,961	2,085
Estimated Fair Value Assets	319	332
Estimated Fair Value Liabilities	8	34
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,692	4,032
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	310	370
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	28,791	28,173
Estimated Fair Value Assets	1,986	2,079
Estimated Fair Value Liabilities	1,872	2,065
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	9,862	10,272
Estimated Fair Value Assets	32	195
Estimated Fair Value Liabilities	181	50
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,583	1,394
Estimated Fair Value Assets	7	47
Estimated Fair Value Liabilities	40	5
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	8,279	8,878
Estimated Fair Value Assets	25	148
Estimated Fair Value Liabilities	141	45
Derivatives Not Designated or Not Qualifying as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	398,202	365,949
Estimated Fair Value Assets	7,662	10,859
Estimated Fair Value Liabilities	5,773	8,001
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	81,178	81,524
Estimated Fair Value Assets	3,284	6,017
Estimated Fair Value Liabilities	1,378	3,328
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	405	613
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	39	25
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate floors
Derivatives, Fair Value [Line Items]
Gross Notional Amount	14,201	14,201
Estimated Fair Value Assets	147	187
Estimated Fair Value Liabilities	2	9
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate caps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	80,060	90,400
Estimated Fair Value Assets	121	137
Estimated Fair Value Liabilities	3	2
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,134	6,081
Estimated Fair Value Assets	6	12
Estimated Fair Value Liabilities	6	12
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	69,059	20,854
Estimated Fair Value Assets	736	764
Estimated Fair Value Liabilities	70	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	4,198	5,425
Estimated Fair Value Assets	6	2
Estimated Fair Value Liabilities	542	738
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Synthetic GICs
Derivatives, Fair Value [Line Items]
Gross Notional Amount	6,428	5,566
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	12,938	12,912
Estimated Fair Value Assets	1,314	1,600
Estimated Fair Value Liabilities	411	466
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	15,688	15,580
Estimated Fair Value Assets	138	126
Estimated Fair Value Liabilities	519	977
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	837	915
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	2	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,650	3,615
Estimated Fair Value Assets	107	195
Estimated Fair Value Liabilities	28	17
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,142	2,038
Estimated Fair Value Assets	5	14
Estimated Fair Value Liabilities	45	40
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Gross Notional Amount	12,369	12,645
Estimated Fair Value Assets	204	189
Estimated Fair Value Liabilities	5	9
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	9,195	12,494
Estimated Fair Value Assets	19	68
Estimated Fair Value Liabilities	8	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity index options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,224	54,028
Estimated Fair Value Assets	1,321	1,323
Estimated Fair Value Liabilities	1,740	1,458
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity variance swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	23,231	23,157
Estimated Fair Value Assets	253	223
Estimated Fair Value Liabilities	835	756
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,265	3,901
Estimated Fair Value Assets	1	2
Estimated Fair Value Liabilities	$ 140	$ 160