Financial Derivatives (Credit Default Swaps) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	$ 110	$ 304
Fair Value	2	11
Average term of credit risk derivatives	22 years 7 months	9 years 10 months
Credit Default Swap, Selling Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives		94	[1]
Fair Value		2	[1]
Average term of credit risk derivatives		1 year 11 months	[1]
Credit Default Swap, Buying Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	110	210
Fair Value	2	9
Average term of credit risk derivatives	22 years 7 months	13 years 4 months
Underlying Other Guarantor Single Name [Member] | Credit Default Swap, Selling Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives		45	[1]
Fair Value		2	[1]
Average term of credit risk derivatives		1 year 10 months	[1]
Underlying Other Sold Index Traded [Member] | Credit Default Swap, Selling Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives		49	[1]
Fair Value
Average term of credit risk derivatives		2 years 0 months	[1]
Underlying Other Beneficiary Single Name [Member] | Credit Default Swap, Buying Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	50	150
Fair Value		5
Average term of credit risk derivatives	6 years 1 month	3 years 10 months
Underlying Other Beneficiary Index Traded [Member] | Credit Default Swap, Buying Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	60	60
Fair Value	$ 2	$ 4
Average term of credit risk derivatives	36 years 5 months	37 years 2 months

[1] There were no credit default swaps sold as of September 30, 2012.