Derivative Financial Instruments (Details 10) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (14)	$ (41)
Maximum Amount of Future Payments under Credit Default Swaps	8,772	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	30	4
Maximum Amount of Future Payments under Credit Default Swaps	3,540	3,550
Weighted Average Years to Maturity	2.6	3.1
Aaa/Aa/A [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	6	5
Maximum Amount of Future Payments under Credit Default Swaps	727	737
Weighted Average Years to Maturity	3.1	3.5
Aaa/Aa/A [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	24	(1)
Maximum Amount of Future Payments under Credit Default Swaps	2,813	2,813
Weighted Average Years to Maturity	2.5	3.0
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(22)	(43)
Maximum Amount of Future Payments under Credit Default Swaps	4,934	4,081
Weighted Average Years to Maturity	4.0	4.6
Baa [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(14)	(17)
Maximum Amount of Future Payments under Credit Default Swaps	1,479	1,234
Weighted Average Years to Maturity	3.8	4.0
Baa [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(21)	(26)
Maximum Amount of Future Payments under Credit Default Swaps	3,455	2,847
Weighted Average Years to Maturity	5.0	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	25	25
Weighted Average Years to Maturity	3.0	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	25	25
Weighted Average Years to Maturity	3.0	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	0
B [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(9)	(2)
Maximum Amount of Future Payments under Credit Default Swaps	273	25
Weighted Average Years to Maturity	5.0	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	0
B [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(9)	(2)
Maximum Amount of Future Payments under Credit Default Swaps	$ 273	$ 25
Weighted Average Years to Maturity	5.0	4.8