Derivatives (Details 7) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 74	$ (41)
Maximum Amount of Future Payments under Credit Default Swaps	8,879	7,681
Weighted Average Years to Maturity	3 years 7 months 6 days	3 years 10 months 24 days
Aaa/Aa/A [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	52	4
Maximum Amount of Future Payments under Credit Default Swaps	3,490	3,550
Weighted Average Years to Maturity	2 years 2 months 12 days	3 years 1 month 6 days
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	777	737
Weighted Average Years to Maturity	2 years 8 months 12 days	3 years 6 months 0 days
Aaa/Aa/A [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	42	(1)
Maximum Amount of Future Payments under Credit Default Swaps	2,713	2,813
Weighted Average Years to Maturity	2 years 1 month 6 days	3 years
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	19	(43)
Maximum Amount of Future Payments under Credit Default Swaps	5,064	4,081
Weighted Average Years to Maturity	4 years 6 months 0 days	4 years 7 months 6 days
Baa [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	8	(17)
Maximum Amount of Future Payments under Credit Default Swaps	1,314	1,234
Weighted Average Years to Maturity	3 years 4 months 24 days	4 years
Baa [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	11	(26)
Maximum Amount of Future Payments under Credit Default Swaps	3,750	2,847
Weighted Average Years to Maturity	4 years 10 months 24 days	4 years 10 months 24 days
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 8 months 12 days	3 years 6 months 0 days
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 8 months 12 days	3 years 6 months 0 days
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	3	(2)
Maximum Amount of Future Payments under Credit Default Swaps	300	25
Weighted Average Years to Maturity	4 years 10 months 24 days	4 years 9 months 18 days
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	3	(2)
Maximum Amount of Future Payments under Credit Default Swaps	$ 300	$ 25
Weighted Average Years to Maturity	4 years 10 months 24 days	4 years 9 months 18 days