Derivatives (Primary Risks) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Gross Notional Amount	$ 418,148	$ 404,844
Estimated Fair Value Assets	15,761	14,406
Estimated Fair Value Liabilities	10,804	7,049
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	52,199	46,808
Estimated Fair Value Assets	4,902	4,358
Estimated Fair Value Liabilities	2,803	2,074
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	7,637	9,367
Estimated Fair Value Assets	2,296	2,277
Estimated Fair Value Liabilities	284	223
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,331	5,528
Estimated Fair Value Assets	2,262	2,215
Estimated Fair Value Liabilities	6	12
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,221	2,154
Estimated Fair Value Assets	34	62
Estimated Fair Value Liabilities	224	159
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,085	1,685
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	54	52
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	34,290	25,956
Estimated Fair Value Assets	2,411	1,813
Estimated Fair Value Liabilities	2,469	1,803
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,085	2,190
Estimated Fair Value Assets	332	487
Estimated Fair Value Liabilities	34	0
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	4,032	105
Estimated Fair Value Assets	0	23
Estimated Fair Value Liabilities	370	0
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	28,173	23,661
Estimated Fair Value Assets	2,079	1,303
Estimated Fair Value Liabilities	2,065	1,803
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	10,272	11,485
Estimated Fair Value Assets	195	268
Estimated Fair Value Liabilities	50	48
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,394	3,916
Estimated Fair Value Assets	47	63
Estimated Fair Value Liabilities	5	12
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Currency options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	8,878	7,569
Estimated Fair Value Assets	148	205
Estimated Fair Value Liabilities	45	36
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	365,949	358,036
Estimated Fair Value Assets	10,859	10,048
Estimated Fair Value Liabilities	8,001	4,975
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	81,524	89,288
Estimated Fair Value Assets	6,017	5,109
Estimated Fair Value Liabilities	3,328	2,247
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	613	43
Estimated Fair Value Assets	0	1
Estimated Fair Value Liabilities	25	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate floors
Derivatives, Fair Value [Line Items]
Gross Notional Amount	14,201	23,837
Estimated Fair Value Assets	187	311
Estimated Fair Value Liabilities	9	48
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate caps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	90,400	68,928
Estimated Fair Value Assets	137	105
Estimated Fair Value Liabilities	2	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	6,081	5,808
Estimated Fair Value Assets	12	4
Estimated Fair Value Liabilities	12	7
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	20,854	30,234
Estimated Fair Value Assets	764	1,177
Estimated Fair Value Liabilities	1	30
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Synthetic GICs
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,566	4,216
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	12,912	11,081
Estimated Fair Value Assets	1,600	766
Estimated Fair Value Liabilities	466	431
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	15,580	11,724
Estimated Fair Value Assets	126	154
Estimated Fair Value Liabilities	977	220
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Currency futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	915	930
Estimated Fair Value Assets	0	0
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	3,615	9,590
Estimated Fair Value Assets	195	466
Estimated Fair Value Liabilities	17	189
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,038	1,870
Estimated Fair Value Assets	14	28
Estimated Fair Value Liabilities	40	34
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Gross Notional Amount	12,645	10,311
Estimated Fair Value Assets	189	78
Estimated Fair Value Liabilities	9	13
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	12,494	7,206
Estimated Fair Value Assets	68	63
Estimated Fair Value Liabilities	3	18
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity index options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	54,028	55,682
Estimated Fair Value Assets	1,323	1,542
Estimated Fair Value Liabilities	1,458	1,041
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity variance swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	23,157	23,437
Estimated Fair Value Assets	223	195
Estimated Fair Value Liabilities	756	636
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Total rate of return swaps [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	5,425	48
Estimated Fair Value Assets	2	2
Estimated Fair Value Liabilities	738	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity Total Return Swaps [Member]
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,901	3,803
Estimated Fair Value Assets	2	47
Estimated Fair Value Liabilities	$ 160	$ 58