Derivative Financial Instruments (Details 10) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (119)	$ 62
Maximum Amount of Future Payments under Credit Default Swaps	7,780	5,089
Weighted Average Years to Maturity	4.1	4.1
Aaa/Aa/A [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(29)	50
Maximum Amount of Future Payments under Credit Default Swaps	3,633	3,398
Weighted Average Years to Maturity	3.4	3.7
Aaa/Aa/A [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	3	5
Maximum Amount of Future Payments under Credit Default Swaps	820	470
Weighted Average Years to Maturity	3.7	3.8
Aaa/Aa/A [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(32)	45
Maximum Amount of Future Payments under Credit Default Swaps	2,813	2,928
Weighted Average Years to Maturity	3.2	3.7
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(88)	12
Maximum Amount of Future Payments under Credit Default Swaps	4,092	1,666
Weighted Average Years to Maturity	4.8	4.7
Baa [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(34)	5
Maximum Amount of Future Payments under Credit Default Swaps	1,320	735
Weighted Average Years to Maturity	4.3	4.3
Baa [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(54)	7
Maximum Amount of Future Payments under Credit Default Swaps	2,772	931
Weighted Average Years to Maturity	5.1	5.0
Ba [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	1	0
Maximum Amount of Future Payments under Credit Default Swaps	30	25
Weighted Average Years to Maturity	3.9	4.4
Ba [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	1	0
Maximum Amount of Future Payments under Credit Default Swaps	30	25
Weighted Average Years to Maturity	3.9	4.4
Ba [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	0	0
Maximum Amount of Future Payments under Credit Default Swaps	0	0
Weighted Average Years to Maturity	0	0
B [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(1)	0
Maximum Amount of Future Payments under Credit Default Swaps	25	0
Weighted Average Years to Maturity	5.0	0
B [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	0	0
Maximum Amount of Future Payments under Credit Default Swaps	0	0
Weighted Average Years to Maturity	0	0
B [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(1)	0
Maximum Amount of Future Payments under Credit Default Swaps	$ 25	$ 0
Weighted Average Years to Maturity	5.0	0