Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gross Notional Amount	$ 294,125	$ 286,643
Estimated Fair Value Assets	8,792	12,139
Estimated Fair Value Liabilities	4,668	6,921
Derivatives Designated as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,419	50,351
Estimated Fair Value Assets	4,002	4,652
Estimated Fair Value Liabilities	1,982	2,792
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	7,241	7,327
Estimated Fair Value Assets	2,352	2,255
Estimated Fair Value Liabilities	73	284
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,959	5,021
Estimated Fair Value Assets	2,305	2,221
Estimated Fair Value Liabilities	3	6
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	658	1,221
Estimated Fair Value Assets	47	34
Estimated Fair Value Liabilities	5	224
Derivatives Designated as Hedging Instruments: | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,624	1,085
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	65	54
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	37,944	32,752
Estimated Fair Value Assets	1,612	2,202
Estimated Fair Value Liabilities	1,774	2,458
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,781	2,040
Estimated Fair Value Assets	308	325
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	3,412	4,032
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	203	370
Derivatives Designated as Hedging Instruments: | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	30,751	26,680
Estimated Fair Value Assets	1,304	1,877
Estimated Fair Value Liabilities	1,563	2,054
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	9,234	10,272
Estimated Fair Value Assets	38	195
Estimated Fair Value Liabilities	135	50
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	975	1,394
Estimated Fair Value Assets	10	47
Estimated Fair Value Liabilities	24	5
Derivatives Designated as Hedging Instruments: | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	8,259	8,878
Estimated Fair Value Assets	28	148
Estimated Fair Value Liabilities	111	45
Derivatives Not Designated or Not Qualifying as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Gross Notional Amount	239,706	236,292
Estimated Fair Value Assets	4,790	7,487
Estimated Fair Value Liabilities	2,686	4,129
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	59,494	53,349
Estimated Fair Value Assets	2,246	4,089
Estimated Fair Value Liabilities	570	1,641
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	217	613
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	37	25
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate floors
Derivatives, Fair Value [Line Items]
Gross Notional Amount	7,201	12,101
Estimated Fair Value Assets	128	181
Estimated Fair Value Liabilities	0	7
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate caps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	73,018	78,358
Estimated Fair Value Assets	54	112
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	4,256	4,793
Estimated Fair Value Assets	13	3
Estimated Fair Value Liabilities	0	12
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Interest rate options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	12,009	5,334
Estimated Fair Value Assets	657	628
Estimated Fair Value Liabilities	35	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,048	1,549
Estimated Fair Value Assets	3	2
Estimated Fair Value Liabilities	9	127
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Synthetic GICs
Derivatives, Fair Value [Line Items]
Gross Notional Amount	11,254	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	10,509	11,651
Estimated Fair Value Assets	796	1,445
Estimated Fair Value Liabilities	426	462
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	16,502	15,422
Estimated Fair Value Assets	95	117
Estimated Fair Value Liabilities	527	977
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Currency futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	874	915
Estimated Fair Value Assets	0	0
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	2,929	3,615
Estimated Fair Value Assets	42	195
Estimated Fair Value Liabilities	3	17
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,329	2,001
Estimated Fair Value Assets	11	14
Estimated Fair Value Liabilities	46	40
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Gross Notional Amount	11,946	10,732
Estimated Fair Value Assets	256	161
Estimated Fair Value Liabilities	1	9
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	4,309	4,457
Estimated Fair Value Assets	4	30
Estimated Fair Value Liabilities	28	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity index options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	12,371	16,527
Estimated Fair Value Assets	382	426
Estimated Fair Value Liabilities	679	523
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity variance swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	8,337	8,263
Estimated Fair Value Assets	103	83
Estimated Fair Value Liabilities	285	240
Derivatives Not Designated or Not Qualifying as Hedging Instruments: | Equity total return swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,103	1,046
Estimated Fair Value Assets	0	1
Estimated Fair Value Liabilities	$ 35	$ 43