Derivative Financial Instruments (Details 10) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 57	$ (41)
Maximum Amount of Future Payments under Credit Default Swaps	7,835	7,681
Weighted Average Years to Maturity	3.9	3.9
Aaa/Aa/A [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	46	4
Maximum Amount of Future Payments under Credit Default Swaps	3,495	3,550
Weighted Average Years to Maturity	2.8	3.1
Aaa/Aa/A [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	9	5
Maximum Amount of Future Payments under Credit Default Swaps	682	737
Weighted Average Years to Maturity	3.2	3.5
Aaa/Aa/A [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	37	(1)
Maximum Amount of Future Payments under Credit Default Swaps	2,813	2,813
Weighted Average Years to Maturity	2.8	3.0
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	14	(43)
Maximum Amount of Future Payments under Credit Default Swaps	4,150	4,081
Weighted Average Years to Maturity	4.7	4.6
Baa [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	1	(17)
Maximum Amount of Future Payments under Credit Default Swaps	1,219	1,234
Weighted Average Years to Maturity	3.9	4.0
Baa [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	13	(26)
Maximum Amount of Future Payments under Credit Default Swaps	2,931	2,847
Weighted Average Years to Maturity	5.1	4.9
Ba [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	0	0
Maximum Amount of Future Payments under Credit Default Swaps	40	25
Weighted Average Years to Maturity	3.6	3.5
Ba [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	40	25
Weighted Average Years to Maturity	3.6	3.5
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	(3)	(2)
Maximum Amount of Future Payments under Credit Default Swaps	150	25
Weighted Average Years to Maturity	5.2	4.8
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	(3)	(2)
Maximum Amount of Future Payments under Credit Default Swaps	$ 150	$ 25
Weighted Average Years to Maturity	5.2	4.8