Derivatives (Credit Derivatives) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 125	$ 123
Maximum Amount of Future Payments under Credit Default Swaps	7,419	6,600
Weighted Average Years to Maturity	3 years 9 months	3 years 5 months 0 days
Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	15	26
Maximum Amount of Future Payments under Credit Default Swaps	1,981	2,484
Weighted Average Years to Maturity	2 years 7 months	1 year 8 months 20 days
Aaa/Aa/A | Single name credit default swaps (corporate)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	5	6
Maximum Amount of Future Payments under Credit Default Swaps	415	395
Weighted Average Years to Maturity	2 years 2 months	2 years 6 months 20 days
Aaa/Aa/A | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	10	20
Maximum Amount of Future Payments under Credit Default Swaps	1,566	2,089
Weighted Average Years to Maturity	2 years 8 months	1 year 6 months 26 days
Baa
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	74	68
Maximum Amount of Future Payments under Credit Default Swaps	4,689	3,772
Weighted Average Years to Maturity	4 years 1 month	4 years 4 months 20 days
Baa | Single name credit default swaps (corporate)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	15	16
Maximum Amount of Future Payments under Credit Default Swaps	1,002	874
Weighted Average Years to Maturity	2 years 9 months	3 years 2 months 12 days
Baa | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	59	52
Maximum Amount of Future Payments under Credit Default Swaps	3,687	2,898
Weighted Average Years to Maturity	4 years 6 months	4 years 8 months 4 days
Ba
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(1)	0
Maximum Amount of Future Payments under Credit Default Swaps	160	5
Weighted Average Years to Maturity	2 years 5 months	3 years 9 months 12 days
Ba | Single name credit default swaps (corporate)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	0	0
Maximum Amount of Future Payments under Credit Default Swaps	60	5
Weighted Average Years to Maturity	3 years	3 years 9 months 12 days
Ba | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	(1)	0
Maximum Amount of Future Payments under Credit Default Swaps	100	0
Weighted Average Years to Maturity	2 years	0 years
B
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	37	29
Maximum Amount of Future Payments under Credit Default Swaps	589	339
Weighted Average Years to Maturity	4 years 11 months	4 years 10 months 24 days
B | Single name credit default swaps (corporate)
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 | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	37	29
Maximum Amount of Future Payments under Credit Default Swaps	$ 589	$ 339
Weighted Average Years to Maturity	4 years 11 months	4 years 10 months 24 days