Derivative Financial Instruments (Details 10) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 60		$ (41)
Maximum Amount of Future Payments under Credit Default Swaps	8,687		7,681
Weighted Average Years to Maturity	3 years 8 months	3 years 9 months
Aaa/Aa/A [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	49		4
Maximum Amount of Future Payments under Credit Default Swaps	3,555		3,550
Weighted Average Years to Maturity	2 years 5 months	3 years 1 month
Aaa/Aa/A [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	10		5
Maximum Amount of Future Payments under Credit Default Swaps	742		737
Weighted Average Years to Maturity	2 years 9 months	3 years 6 months
Aaa/Aa/A [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	39		(1)
Maximum Amount of Future Payments under Credit Default Swaps	2,813		2,813
Weighted Average Years to Maturity	2 years 3 months	3 years
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	9		(43)
Maximum Amount of Future Payments under Credit Default Swaps	4,834		4,081
Weighted Average Years to Maturity	4 years 7 months	4 years 6 months
Baa [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	3		(17)
Maximum Amount of Future Payments under Credit Default Swaps	1,329		1,234
Weighted Average Years to Maturity	3 years 6 months	4 years
Baa [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	6		(26)
Maximum Amount of Future Payments under Credit Default Swaps	3,505		2,847
Weighted Average Years to Maturity	5 years	4 years 9 months
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	2 years 11 months	3 years 5 months
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	2 years 11 months	3 years 5 months
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 years	0 years
B [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	2		(2)
Maximum Amount of Future Payments under Credit Default Swaps	273		25
Weighted Average Years to Maturity	4 years 8 months	4 years 8 months
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 years	0 years
B [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	2		(2)
Maximum Amount of Future Payments under Credit Default Swaps	$ 273		$ 25
Weighted Average Years to Maturity	4 years 8 months	4 years 8 months