Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Notional Amount	$ 49,439	$ 45,623
Estimated Fair Value Assets	2,529	2,766
Estimated Fair Value Liabilities	876	680
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	47,093	43,294
Estimated Fair Value Assets	2,239	2,288
Estimated Fair Value Liabilities	838	643
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	16,530	12,408
Estimated Fair Value Assets	1,314	1,287
Estimated Fair Value Liabilities	595	421
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate floors [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	7,986	7,986
Estimated Fair Value Assets	357	330
Estimated Fair Value Liabilities	158	152
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Interest rate caps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	9,113	10,133
Estimated Fair Value Assets	12	19
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Futures [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	3,468	3,766
Estimated Fair Value Assets	0	10
Estimated Fair Value Liabilities	1	1
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Forward Contracts [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] | Foreign currency swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	753	749
Estimated Fair Value Assets	62	78
Estimated Fair Value Liabilities	33	31
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Foreign currency forwards [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	140	149
Estimated Fair Value Assets	1	9
Estimated Fair Value Liabilities	1	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Credit default swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	2,679	2,426
Estimated Fair Value Assets	21	18
Estimated Fair Value Liabilities	4	28
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Equity futures [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	1,069	1,007
Estimated Fair Value Assets	6	4
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Stock Option [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	2,626	2,111
Estimated Fair Value Assets	447	482
Estimated Fair Value Liabilities	0	0
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Variance swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	2,580	2,430
Estimated Fair Value Assets	15	51
Estimated Fair Value Liabilities	46	8
Derivatives Not Designated or Not Qualifying as Hedging Instruments [Member] | Total rate of return swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	149	129
Estimated Fair Value Assets	4	0
Estimated Fair Value Liabilities	$ 0	$ 2