Derivatives (Primary Risks) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Gross Notional Amount	$ 121,941	$ 132,802
Estimated Fair Value Assets	4,241	3,576
Estimated Fair Value Liabilities	1,980	1,818
Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,602	1,631
Estimated Fair Value Assets	300	215
Estimated Fair Value Liabilities	7	11
Derivatives Designated as Hedging Instruments | Fair Value Hedges
Derivatives, Fair Value [Line Items]
Gross Notional Amount	369	379
Estimated Fair Value Assets	42	33
Estimated Fair Value Liabilities	2	2
Derivatives Designated as Hedging Instruments | Fair Value Hedges | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	369	379
Estimated Fair Value Assets	42	33
Estimated Fair Value Liabilities	2	2
Derivatives Designated as Hedging Instruments | Fair Value Hedges | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	0	0
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	0	0
Derivatives Designated as Hedging Instruments | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,233	1,252
Estimated Fair Value Assets	258	182
Estimated Fair Value Liabilities	5	9
Derivatives Designated as Hedging Instruments | Cash Flow Hedges | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	335	369
Estimated Fair Value Assets	103	81
Estimated Fair Value Liabilities	0	0
Derivatives Designated as Hedging Instruments | Cash Flow Hedges | Interest rate forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	130	155
Estimated Fair Value Assets	48	45
Estimated Fair Value Liabilities	0	0
Derivatives Designated as Hedging Instruments | Cash Flow Hedges | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	768	728
Estimated Fair Value Assets	107	56
Estimated Fair Value Liabilities	5	9
Derivatives Not Designated or Not Qualifying as Hedging Instruments
Derivatives, Fair Value [Line Items]
Gross Notional Amount	120,339	131,171
Estimated Fair Value Assets	3,941	3,361
Estimated Fair Value Liabilities	1,973	1,807
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Interest rate swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	25,078	25,919
Estimated Fair Value Assets	2,019	1,709
Estimated Fair Value Liabilities	761	601
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Interest rate floors
Derivatives, Fair Value [Line Items]
Gross Notional Amount	13,504	16,404
Estimated Fair Value Assets	77	83
Estimated Fair Value Liabilities	63	69
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Interest rate caps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	7,901	7,901
Estimated Fair Value Assets	6	11
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Interest rate futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	730	325
Estimated Fair Value Assets	2	1
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Interest rate options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	18,870	29,870
Estimated Fair Value Assets	694	446
Estimated Fair Value Liabilities	1	16
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	751	672
Estimated Fair Value Assets	81	59
Estimated Fair Value Liabilities	1	4
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Gross Notional Amount	49	48
Estimated Fair Value Assets	6	3
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Credit default swaps — purchased
Derivatives, Fair Value [Line Items]
Gross Notional Amount	45	45
Estimated Fair Value Assets	0	0
Estimated Fair Value Liabilities	1	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Credit default swaps — written
Derivatives, Fair Value [Line Items]
Gross Notional Amount	1,851	1,924
Estimated Fair Value Assets	30	29
Estimated Fair Value Liabilities	1	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Equity futures
Derivatives, Fair Value [Line Items]
Gross Notional Amount	3,238	3,086
Estimated Fair Value Assets	21	34
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Equity index options
Derivatives, Fair Value [Line Items]
Gross Notional Amount	30,631	27,212
Estimated Fair Value Assets	881	854
Estimated Fair Value Liabilities	639	613
Derivatives Not Designated or Not Qualifying as Hedging Instruments | Equity variance swaps
Derivatives, Fair Value [Line Items]
Gross Notional Amount	15,283	15,433
Estimated Fair Value Assets	118	120
Estimated Fair Value Liabilities	450	435
Derivatives Not Designated or Not Qualifying as Hedging Instruments | TRRs
Derivatives, Fair Value [Line Items]
Gross Notional Amount	2,408	2,332
Estimated Fair Value Assets	6	12
Estimated Fair Value Liabilities	$ 56	$ 67