Financial Derivatives (Credit Default Swaps) (Details) (Credit Default Swap, Buying Protection [Member], USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	$ 95	$ 110
Fair Value	2	2
Average term of credit risk derivatives	25 years 5 months	22 years 5 months
Underlying Other Beneficiary Single Name [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	35	50
Fair Value
Average term of credit risk derivatives	7 years 9 months	5 years 10 months
Underlying Other Beneficiary Index Traded [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	60	60
Fair Value	$ 2	$ 2
Average term of credit risk derivatives	35 years 9 months	36 years 1 month