Derivatives (Credit Derivatives) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 139	$ 165
Maximum Amount of Future Payments under Credit Default Swaps	9,848	9,055
Weighted Average Years to Maturity	3 years 6 months	3 years 5 months
Aaa/Aa/A [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	25	36
Maximum Amount of Future Payments under Credit Default Swaps	3,823	3,284
Weighted Average Years to Maturity	2 years	1 year 7 months
Aaa/Aa/A [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	9	10
Maximum Amount of Future Payments under Credit Default Swaps	560	545
Weighted Average Years to Maturity	2 years 5 months	2 years 7 months
Aaa/Aa/A [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	16	26
Maximum Amount of Future Payments under Credit Default Swaps	3,263	2,739
Weighted Average Years to Maturity	1 year 11 months	1 year 6 months
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	85	97
Maximum Amount of Future Payments under Credit Default Swaps	5,645	5,391
Weighted Average Years to Maturity	4 years 6 months	4 years 4 months
Baa [Member] | Single name credit default swaps (corporate) [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	21	24
Maximum Amount of Future Payments under Credit Default Swaps	1,485	1,320
Weighted Average Years to Maturity	3 years 1 month	3 years 1 month
Baa [Member] | Credit default swaps referencing indices [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	64	73
Maximum Amount of Future Payments under Credit Default Swaps	4,160	4,071
Weighted Average Years to Maturity	5 years	4 years 8 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	5	5
Weighted Average Years to Maturity	3 years 6 months	3 years 9 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	5	5
Weighted Average Years to Maturity	3 years 6 months	3 years 9 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	29	32
Maximum Amount of Future Payments under Credit Default Swaps	375	375
Weighted Average Years to Maturity	5 years 1 month	4 years 11 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	29	32
Maximum Amount of Future Payments under Credit Default Swaps	$ 375	$ 375
Weighted Average Years to Maturity	5 years 1 month	4 years 11 months