Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 158		$ 175
Maximum Amount of Future Payments under Credit Default Swaps	$ 10,594		$ 10,527
Weighted Average Years to Maturity	4 years		3 years 11 months
Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 14		$ 20
Maximum Amount of Future Payments under Credit Default Swaps	$ 2,307		$ 2,377
Weighted Average Years to Maturity	2 years 10 months		2 years 7 months
Aaa/Aa/A | Single name credit default swaps (corporate)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 9		$ 10
Maximum Amount of Future Payments under Credit Default Swaps	$ 707		$ 677
Weighted Average Years to Maturity	2 years 6 months		2 years 5 months
Aaa/Aa/A | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5		$ 10
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,600		$ 1,700
Weighted Average Years to Maturity	2 years 11 months		2 years 7 months
Baa
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 101		$ 117
Maximum Amount of Future Payments under Credit Default Swaps	$ 7,428		$ 7,365
Weighted Average Years to Maturity	4 years 4 months		4 years 4 months
Baa | Single name credit default swaps (corporate)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 20		$ 23
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,438		$ 1,591
Weighted Average Years to Maturity	2 years 8 months		2 years 10 months
Baa | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 81		$ 94
Maximum Amount of Future Payments under Credit Default Swaps	$ 5,990		$ 5,774
Weighted Average Years to Maturity	4 years 8 months		4 years 8 months
Ba
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 1		$ (1)
Maximum Amount of Future Payments under Credit Default Swaps	$ 165		$ 160
Weighted Average Years to Maturity	1 year 11 months		2 years 5 months
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	$ 65		$ 60
Weighted Average Years to Maturity	2 years 7 months		3 years
Ba | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 1		$ (1)
Maximum Amount of Future Payments under Credit Default Swaps	$ 100		100
Weighted Average Years to Maturity	1 year 6 months	2 years
B
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 42		39
Maximum Amount of Future Payments under Credit Default Swaps	$ 694		$ 625
Weighted Average Years to Maturity	4 years 11 months		4 years 11 months
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
B | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 42		$ 39
Maximum Amount of Future Payments under Credit Default Swaps	$ 694		$ 625
Weighted Average Years to Maturity	4 years 11 months		4 years 11 months