Financial Derivatives (Credit Default Swaps) (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	$ 493	$ 761
Estimated Net Fair Value	13	16
Weighted-Average Remaining Maturity in Years	7.0	12.5
Underlying Other Guarantor Single Name [Member] | Credit Default Swap, Selling Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	45	45
Estimated Net Fair Value	1	4
Weighted-Average Remaining Maturity in Years	2.1	2.8
Underlying Other Sold Index Traded [Member] | Credit Default Swap, Selling Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	118	189
Estimated Net Fair Value		2
Weighted-Average Remaining Maturity in Years	1.9	2.0
Underlying Other Beneficiary Single Name [Member] | Credit Default Swap, Buying Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	270	317
Estimated Net Fair Value	6	2
Weighted-Average Remaining Maturity in Years	3.3	2.6
Underlying Other Beneficiary Index Traded [Member] | Credit Default Swap, Buying Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	60	210
Estimated Net Fair Value	6	8
Weighted-Average Remaining Maturity in Years	37.5	38.8
Underlying Others [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	493	761
Credit Default Swap, Selling Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	163	234
Estimated Net Fair Value	1	6
Weighted-Average Remaining Maturity in Years	1.9	2.2
Credit Default Swap, Buying Protection [Member]
Credit Derivatives [Line Items]
Notional Amount of Credit Risk Derivatives	330	527
Estimated Net Fair Value	$ 12	$ 10
Weighted-Average Remaining Maturity in Years	9.5	17.0