Financial Derivatives (Credit Default Swaps) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Credit Default Swap [Member] | Underlying Other Guarantor Single Name [Member]
Notional Amount of Credit Risk Derivatives	$ 45	$ 45
Estimated Net Fair Value	4	4
Weighted-Average Remaining Maturity in Years	2.3	2.8
Underlying Other Guarantor [Member]
Notional Amount of Credit Risk Derivatives	163	234
Underlying Other Guarantor [Member] | Credit Default Swap [Member]
Notional Amount of Credit Risk Derivatives	163	234
Estimated Net Fair Value	5	6
Weighted-Average Remaining Maturity in Years	2.2	2.2
Credit Default Swap [Member] | Underlying Other Sold Index Traded [Member]
Notional Amount of Credit Risk Derivatives	118	189
Estimated Net Fair Value	1	2
Weighted-Average Remaining Maturity in Years	2.1	2.0
Credit Default Swap [Member] | Underlying Other Beneficiary Single Name [Member]
Notional Amount of Credit Risk Derivatives	310	317
Estimated Net Fair Value	1	2
Weighted-Average Remaining Maturity in Years	3.3	2.6
Credit Default Swap [Member] | Underlying Other Beneficiary Index Traded [Member]
Notional Amount of Credit Risk Derivatives	110	210
Estimated Net Fair Value	6	8
Weighted-Average Remaining Maturity in Years	38.2	38.8
Credit Default Swap [Member] | Underlying Other Beneficiary [Member]
Notional Amount of Credit Risk Derivatives	420	527
Estimated Net Fair Value	7	10
Weighted-Average Remaining Maturity in Years	12.5	17.0
Underlying Other Beneficiary [Member]
Notional Amount of Credit Risk Derivatives	420	527
Credit Default Swap [Member] | Underlying Others [Member]
Notional Amount of Credit Risk Derivatives	583	761
Estimated Net Fair Value	12	16
Weighted-Average Remaining Maturity in Years	9.6	12.5
Underlying Others [Member]
Notional Amount of Credit Risk Derivatives	$ 583	$ 761