Financial Derivatives (Credit Ratings of Credit Default Swaps) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Notional Amount of Credit Risk Derivatives	$ 493		$ 761
Underlying Other Guarantor [Member]
Notional Amount of Credit Risk Derivatives	163		234
Underlying Other Guarantor [Member] | External Credit Rating, Investment Grade [Member]
Notional Amount of Credit Risk Derivatives	139	[1]	220	[1]
Underlying Other Guarantor [Member] | External Credit Rating, Non Investment Grade [Member]
Notional Amount of Credit Risk Derivatives	24	[2]	14	[2]
Underlying Other Beneficiary [Member]
Notional Amount of Credit Risk Derivatives	330		527
Underlying Other Beneficiary [Member] | External Credit Rating, Investment Grade [Member]
Notional Amount of Credit Risk Derivatives	235	[1]	385	[1]
Underlying Other Beneficiary [Member] | External Credit Rating, Non Investment Grade [Member]
Notional Amount of Credit Risk Derivatives	95	[2]	142	[2]
Underlying Others [Member]
Notional Amount of Credit Risk Derivatives	$ 493		$ 761

[1] Investment grade with a rating of BBB-/Baa3 or above based on published rating agency information.

[2] Subinvestment grade with a rating below BBB-/Baa3 based on published rating agency information.