Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gross Notional Amount	$ 434,881	$ 418,148
Estimated Fair Value Assets	12,178	15,761
Estimated Fair Value Liabilities	8,217	10,804
Derivatives Designated as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,918	52,199
Estimated Fair Value Assets	4,386	4,902
Estimated Fair Value Liabilities	2,233	2,803
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	7,154	7,637
Estimated Fair Value Assets	2,374	2,296
Estimated Fair Value Liabilities	64	284
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	4,347	5,331
Estimated Fair Value Assets	2,326	2,262
Estimated Fair Value Liabilities	5	6
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	632	1,221
Estimated Fair Value Assets	48	34
Estimated Fair Value Liabilities	0	224
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,175	1,085
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	59	54
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	37,596	34,290
Estimated Fair Value Assets	1,971	2,411
Estimated Fair Value Liabilities	2,004	2,469
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,886	2,085
Estimated Fair Value Assets	331	332
Estimated Fair Value Liabilities	16	34
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,542	4,032
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	210	370
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	30,168	28,173
Estimated Fair Value Assets	1,640	2,079
Estimated Fair Value Liabilities	1,778	2,065
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	10,168	10,272
Estimated Fair Value Assets	41	195
Estimated Fair Value Liabilities	165	50
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,932	1,394
Estimated Fair Value Assets	7	47
Estimated Fair Value Liabilities	51	5
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	8,236	8,878
Estimated Fair Value Assets	34	148
Estimated Fair Value Liabilities	114	45
Derivatives Not Designated or Not Qualifying as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	379,963	365,949
Estimated Fair Value Assets	7,792	10,859
Estimated Fair Value Liabilities	5,984	8,001
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	82,022	81,524
Estimated Fair Value Assets	3,396	6,017
Estimated Fair Value Liabilities	1,465	3,328
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	358	613
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	34	25
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate floors
Derivatives, Fair Value [Line Items]
Gross Notional Amount	7,201	14,201
Estimated Fair Value Assets	136	187
Estimated Fair Value Liabilities	0	9
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate caps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	81,560	90,400
Estimated Fair Value Assets	72	137
Estimated Fair Value Liabilities	2	2
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,143	6,081
Estimated Fair Value Assets	24	12
Estimated Fair Value Liabilities	2	12
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	32,884	20,854
Estimated Fair Value Assets	822	764
Estimated Fair Value Liabilities	48	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	26	2
Estimated Fair Value Liabilities	389	738
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Synthetic GICs
Derivatives, Fair Value [Line Items]
Gross Notional Amount	6,305	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	13,031	12,912
Estimated Fair Value Assets	1,071	1,600
Estimated Fair Value Liabilities	451	466
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	17,206	15,580
Estimated Fair Value Assets	103	126
Estimated Fair Value Liabilities	572	977
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	869	915
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	4	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,481	3,615
Estimated Fair Value Assets	51	195
Estimated Fair Value Liabilities	0	17
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,955	2,038
Estimated Fair Value Assets	8	14
Estimated Fair Value Liabilities	42	40
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Gross Notional Amount	13,377	12,645
Estimated Fair Value Assets	259	189
Estimated Fair Value Liabilities	4	9
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	7,904	12,494
Estimated Fair Value Assets	12	68
Estimated Fair Value Liabilities	3	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity index options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	77,608	54,028
Estimated Fair Value Assets	1,543	1,323
Estimated Fair Value Liabilities	2,024	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	266	223
Estimated Fair Value Liabilities	866	756
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,630	3,901
Estimated Fair Value Assets	3	2
Estimated Fair Value Liabilities	$ 78	$ 160