Derivatives (Primary Risks) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Notional Amount	$ 63,427	$ 56,193
Estimated Fair Value Assets	1,600	2,370
Estimated Fair Value Liabilities	811	970
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	1,960	2,252
Estimated Fair Value Assets	55	224
Estimated Fair Value Liabilities	69	37
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	587	660
Estimated Fair Value Assets	6	28
Estimated Fair Value Liabilities	23	23
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	465	538
Estimated Fair Value Assets	6	28
Estimated Fair Value Liabilities	8	9
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedges [Member] | Foreign currency swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	122	122
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	15	14
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	1,373	1,592
Estimated Fair Value Assets	49	196
Estimated Fair Value Liabilities	46	14
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	537	658
Estimated Fair Value Assets	16	99
Estimated Fair Value Liabilities	19	0
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedges [Member] | Interest rate forwards [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	290	410
Estimated Fair Value Assets	12	81
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	546	524
Estimated Fair Value Assets	21	16
Estimated Fair Value Liabilities	27	14
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	61,467	53,941
Estimated Fair Value Assets	1,545	2,146
Estimated Fair Value Liabilities	742	933
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	23,748	16,869
Estimated Fair Value Assets	925	1,254
Estimated Fair Value Liabilities	424	513
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate floors [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	17,604	15,136
Estimated Fair Value Assets	144	318
Estimated Fair Value Liabilities	139	274
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate caps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	8,001	9,031
Estimated Fair Value Assets	29	11
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	1,493	2,771
Estimated Fair Value Assets	1	0
Estimated Fair Value Liabilities	0	7
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Foreign currency swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	823	811
Estimated Fair Value Assets	51	60
Estimated Fair Value Liabilities	44	35
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Foreign currency forwards [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	43	139
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	2	4
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps - purchased [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	194	162
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	2	2
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps - written [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	2,299	2,456
Estimated Fair Value Assets	29	23
Estimated Fair Value Liabilities	0	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity futures [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	774	1,075
Estimated Fair Value Assets	5	0
Estimated Fair Value Liabilities	0	27
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity Options [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	3,453	2,845
Estimated Fair Value Assets	356	469
Estimated Fair Value Liabilities	25	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Variance swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	2,562	2,346
Estimated Fair Value Assets	4	11
Estimated Fair Value Liabilities	97	62
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Total rate of return swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	473	300
Estimated Fair Value Assets	1	0
Estimated Fair Value Liabilities	$ 9	$ 7