Derivatives (Primary Risks) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Notional Amount	$ 372,112	$ 334,351
Estimated Fair Value Assets	12,823	13,777
Estimated Fair Value Liabilities	5,294	5,536
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	32,680	28,866
Estimated Fair Value Assets	3,272	3,402
Estimated Fair Value Liabilities	608	594
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	8,729	8,584
Estimated Fair Value Assets	2,054	2,253
Estimated Fair Value Liabilities	213	175
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	5,438	5,397
Estimated Fair Value Assets	1,802	1,921
Estimated Fair Value Liabilities	74	90
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	3,291	3,187
Estimated Fair Value Assets	252	332
Estimated Fair Value Liabilities	139	85
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency forwards [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	0	0
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	0	0
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	15,169	13,355
Estimated Fair Value Assets	991	1,063
Estimated Fair Value Liabilities	375	355
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	3,482	3,642
Estimated Fair Value Assets	539	705
Estimated Fair Value Liabilities	7	0
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate forwards [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	620	675
Estimated Fair Value Assets	101	139
Estimated Fair Value Liabilities	0	0
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Foreign currency swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	11,007	9,038
Estimated Fair Value Assets	351	219
Estimated Fair Value Liabilities	368	355
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Credit forwards [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	60	0
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	0	0
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	8,782	6,927
Estimated Fair Value Assets	227	86
Estimated Fair Value Liabilities	20	64
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Foreign currency forwards [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	3,782	2,552
Estimated Fair Value Assets	90	43
Estimated Fair Value Liabilities	20	61
Derivatives Designated as Hedging Instruments [Member] | Foreign Operations Hedges [Member] | Currency options [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	5,000	4,375
Estimated Fair Value Assets	137	43
Estimated Fair Value Liabilities	0	3
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	339,432	305,485
Estimated Fair Value Assets	9,551	10,375
Estimated Fair Value Liabilities	4,686	4,942
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	102,074	83,250
Estimated Fair Value Assets	4,834	5,201
Estimated Fair Value Liabilities	1,920	2,043
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate forwards [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	0	0
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate floors [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	56,246	56,246
Estimated Fair Value Assets	1,026	1,174
Estimated Fair Value Liabilities	709	837
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate caps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	37,015	49,465
Estimated Fair Value Assets	81	74
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate futures [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	9,882	11,684
Estimated Fair Value Assets	1	1
Estimated Fair Value Liabilities	16	38
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate options [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	34,474	16,328
Estimated Fair Value Assets	769	640
Estimated Fair Value Liabilities	74	60
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Synthetic GICs [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	4,291	4,162
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 [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	8,694	8,208
Estimated Fair Value Assets	294	199
Estimated Fair Value Liabilities	580	736
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Foreign currency forwards [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	10,836	9,202
Estimated Fair Value Assets	123	26
Estimated Fair Value Liabilities	153	288
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Currency futures [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	1,542	1,408
Estimated Fair Value Assets	1	4
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Currency options [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	730	129
Estimated Fair Value Assets	37	1
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps - purchased [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	3,925	3,674
Estimated Fair Value Assets	14	11
Estimated Fair Value Liabilities	42	34
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps - written [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	8,909	8,879
Estimated Fair Value Assets	91	79
Estimated Fair Value Liabilities	3	5
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity futures [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	6,626	7,008
Estimated Fair Value Assets	1	14
Estimated Fair Value Liabilities	7	132
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity Options [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	29,624	22,920
Estimated Fair Value Assets	2,145	2,825
Estimated Fair Value Liabilities	588	356
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Variance swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	21,023	19,830
Estimated Fair Value Assets	132	122
Estimated Fair Value Liabilities	486	310
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Total rate of return swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	3,541	3,092
Estimated Fair Value Assets	2	4
Estimated Fair Value Liabilities	$ 108	$ 103